MARSBUGS:  
The Electronic Exobiology Newsletter
Volume 5, Number 9, 1 April, 1998.

Editors:

David Thomas, Department of Biological Sciences, University of 
Idaho, Moscow, ID, 83844-3051, USA, thoma457@uidaho.edu or 
Marsbugs@aol.com.

Julian Hiscox, Division of Molecular Biology, IAH Compton 
Laboratory, Berkshire, RG20 7NN, UK.  Julian.Hiscox@bbsrc.ac.uk or 
Marsbug@msn.com

MARSBUGS is published on a weekly to quarterly basis as warranted 
by the number of articles and announcements.  Copyright of this 
compilation exists with the editors, except for specific articles, 
in which instance copyright exists with the author/authors.  E-
mail subscriptions are free, and may be obtained by contacting 
either of the editors.  Article contributions are welcome, and 
should be submitted to either of the two editors.  Contributions 
should include a short biographical statement about the author(s) 
along with the author(s)' correspondence address.  Subscribers are 
advised to make appropriate inquiries before joining societies, 
ordering goods etc.  Back issues and Word97 files suitable for 
printing may be obtained via anonymous FTP at:  
ftp.uidaho.edu/pub/mmbb/marsbugs.  Also, an official web page is 
under construction.  Currently it is part of 
http://members.aol.com/marsbugs/dave.html (right now, the page 
simply points to the FTP site).

The purpose of this newsletter is to provide a channel of 
information for scientists, educators and other persons interested 
in exobiology and related fields.  This newsletter is not intended 
to replace peer-reviewed journals, but to supplement them.  We, 
the editors, envision MARSBUGS as a medium in which people can 
informally present ideas for investigation, questions about 
exobiology, and announcements of upcoming events.

Exobiology is still a relatively young field, and new ideas may 
come out of the most unexpected places.  Subjects may include, but 
are not limited to:  exobiology proper (life on other planets), 
the search for extraterrestrial intelligence (SETI), ecopoeisis/ 
terraformation, Earth from space, planetary biology, primordial 
evolution, space physiology, biological life support systems, and 
human habitation of space and other planets.

INDEX

1)	MARS GLOBAL SURVEYOR TO ATTEMPT IMAGING OF FEATURES OF PUBLIC 
INTEREST
JPL release

2)	MARS GLOBAL SURVEYOR COMPLETES FIRST AEROBRAKING PERIOD AND 
PREPARES TO PHOTOGRAPH THE MARS PATHFINDER LANDING SITE AND 
FEATURES IN THE CYDONIA PLAIN
JPL release

3)	THE "FACE ON MARS"
NASA release

4)	1998 MARS SURVEYOR PROJECT STATUS REPORT
by John McNamee

5)	MARS SURVEYOR OPERATION PROJECT REPORT 
by Glenn Cunningham

6)	RECENT SCIENTIFIC PAPERS ON ALH84001 EXPLAINED WITH 
INSIGHTFUL AND TOTALLY OBJECTIVE COMMENTARIES
by Allan Treiman

7)	MARS SOCIETY FOUNDING CONVENTION
Mars Society release

8)	GALILEO EUROPA MISSION STATUS
JPL release

9)	GALILEO SOLID STATE IMAGING FULL DATA RELEASED
JPL release

10)	TODAY ON GALILEO
JPL releases
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MARS GLOBAL SURVEYOR TO ATTEMPT IMAGING OF FEATURES OF PUBLIC 
INTEREST
JPL release

25 March, 1998

NASA's Mars Global Surveyor spacecraft is about to begin a summer-
long set of scientific observations of the red planet from an 
interim elliptical orbit, including several attempts to take 
images of features of public interest ranging from the Mars 
Pathfinder and Viking mission landing sites to the Cydonia region.  
The spacecraft will turn on its payload of science instruments on 
March 27, about 12 hours after it suspends "aerobraking," a 
technique that lowers the spacecraft's orbit by using atmospheric 
drag each time it passes close to the planet on each looping 
orbit.  Aerobraking will resume in September and continue until 
March 1999, when the spacecraft will be in a final, circular orbit 
for its prime mapping mission.

It will not be possible to predict on which orbit the spacecraft 
will pass closest to specific features on Mars until Global 
Surveyor has established a stable orbit and flight controllers are 
able to project its ground track.  This process should be 
completed in the next few days.  The exact time of observations 
and the schedule for the subsequent availability of photographs on 
the World Wide Web are expected to be announced early next week.

"Global Surveyor will have three opportunities in the next month 
to see each of the sites, including the Cydonia region, location 
of the so-called 'Face on Mars,' " said Glenn E. Cunningham, Mars 
Global Surveyor project manager at NASA's Jet Propulsion 
Laboratory, Pasadena, CA.  "The sites will be visible about once 
every eight days, and we'll have a 30- to- 50-percent chance of 
capturing images of the sites each time."

Several factors limit the chances of obtaining images of specific 
features with the high-resolution mode of the camera on any one 
pass.  These factors are related primarily to uncertainties both 
in the spacecraft's pointing and the knowledge of the spacecraft's 
ground track from its navigation data.  In addition, current maps 
of Mars are derived from Viking data taken more than 20 years ago.  
Data obtained by Global Surveyor's laser altimeter and camera 
during the last few months have indicated that our knowledge of 
specific locations on the surface is uncertain by 1 to 2 
kilometers (0.6 to 1.2 miles).  As a result, the locations of the 
landing sites and specific features in the Cydonia region are not 
precisely known.

In addition, the Mars Pathfinder and Viking landers are very small 
targets to image, even at the closest distance possible, because 
they are the smallest objects that the camera can see.  The 
Cydonia features, on the other hand, are hundreds to thousands of 
times larger and the camera should be able to capture some of the 
features in that area.

Global Surveyor's observations of the Viking and Pathfinder 
landing sites will provide scientists with important information 
from which to tie together surface observations and orbital 
measurements of the planet.  Data from landing sites provide 
"ground truth" for observations of the planet made from space.

As for the "Face on Mars" feature, "Most scientists believe that 
everything we've seen on Mars is of natural origin," said Dr. Carl 
Pilcher, acting science director for solar system exploration in 
NASA's Office of Space Science, Washington, DC.  "However, we also 
believe it is appropriate to seek to resolve speculation about 
features in the Cydonia region by obtaining images when it is 
possible to do so."

Information about Viking observations of the Cydonia region and a 
listing of those images are available on the World Wide Web at 
http://www.hq.nasa.gov/office/pao/facts/HTML/FS-016-HQ.html.

New images of the landing sites and Cydonia region taken by Mars 
Global Surveyor will be available on JPL's Mars news site at:  
http://www.jpl.nasa.gov/marsnews and on the Global Surveyor home 
page at http://mars.jpl.nasa.gov .  These sites will also carry 
detailed schedules of the imaging attempts once they have been 
determined.  Images will also be available on NASA's Planetary 
Photojournal web site at http://photojournal.jpl.nasa.gov.

So far in the aerobraking process, Global Surveyor's orbit has 
been reduced from an initial 45-hour duration to less than 12 
hours.  During the aerobraking hiatus, the spacecraft will be 
orbiting Mars about once every 11.6 hours, passing about 106 miles 
(170 kilometers) above the surface at closest approach and about 
11,100 miles (17,864 kilometers) at its farthest distance from the 
planet.  The pause in aerobraking allows the spacecraft to achieve 
a final orbit with lighting conditions that are optimal for 
science observations.

Mars Global Surveyor is part of a sustained program of Mars 
exploration, managed by JPL for NASA's Office of Space Science, 
Washington, DC.  Lockheed Martin Astronautics, Denver, CO, which 
built and operates the spacecraft, is JPL's industrial partner in 
the mission.  Malin Space Science Systems, Inc., San Diego, CA, 
built and operates the spacecraft camera.  JPL is a division of 
the California Institute of Technology, Pasadena, CA.
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MARS GLOBAL SURVEYOR COMPLETES FIRST AEROBRAKING PERIOD AND 
PREPARES TO PHOTOGRAPH THE MARS PATHFINDER LANDING SITE AND 
FEATURES IN THE CYDONIA PLAIN
JPL release

26 March, 1998

The Mars Global Surveyor spacecraft is about to resume scientific 
observations of the surface of Mars with its first objective to 
attempt to photograph the Mars Pathfinder landing site, the 
features in the Cydonia region, and the Viking lander sites.  
Surveyor is coming up on a period beginning near the end of March 
and continuing for about a month in which orbital and lighting 
conditions will be suitable for these observations.

The opportunities to see these targets from the Surveyor 
spacecraft will occur in three clusters of two and a half days 
each during the next month.  Each target will be visible once in 
each cluster and the clusters will be separated by eight days.  It 
will not be possible to predict on which orbits, and thus, on 
which days, the spacecraft will come closest to the targets until 
after aerobraking has been terminated on Friday, March 27th.  Then 
several orbits of navigation tracking data have been obtained in 
order to pin point Surveyor's new orbital characteristics.

The exact time of the observation opportunities and the schedule 
and process for the release of the resulting photographs will be 
announced in a few days.  Within a few days before the actual 
observations, a detailed sequence of the spacecraft's activities 
will be posted on this web page, and the project staff will 
provide a near real time commentary on the events as they occur.

Surveyor's science instruments will be turned on again on Friday, 
March 27th, after having been off since February 20th when the 
orbital period became too short for both science and aerobraking 
operations to be conducted simultaneously.  Now that aerobraking 
will be on hold for five months, Surveyor can return to acquiring 
science data.  Science acquisition will continue until early 
September when aerobraking will be resumed.

Photographing the Features in the Cydonia Plain

At the launch of the Mars Global Surveyor mission, NASA announced 
that it would re-photograph the Cydonia region of Mars--an area 
that contains a number of features including the famous "Face on 
Mars"--when Surveyor was over that region during its mapping 
mission.  In addition, NASA said it would announce to the public 
when these opportunities would occur and when the resulting 
pictures would be released.  The opportunity to accelerate the 
schedule of photographing these areas significantly before the 
mapping period has been afforded by the recent modification of 
Surveyor's mission.  This modification was made to extend 
aerobraking for a year in order to compensate for a structural 
weakness discovered in one of Surveyors solar panels.

Targets for Observations

Mars Pathfinder landed last July 4th, deployed the Sojourner rover 
and captivated world interest as it explored a small region in 
Aris Vallis.  The two Viking landers that NASA placed on the 
surface of Mars in 1976 conducted inconclusive experiments to try 
to discover life in the Martian soil.  The Cydonia region has 
become notable from the discovery of an object that looks much 
like a human face in several pictures taken by the Viking Orbiter 
spacecraft over 20 years ago.  Some researchers have proposed 
arguments that the "Face" and other objects in its vicinity are 
artifacts of an extinct civilization and have pressed NASA for 
further investigations of the region.

Latitude and Longitude of four targets located in East longitude
Target			Latitude		Longitude
Cydonia Region		41.0 North	350.5 East
Pathfinder		19.01 North	33.52 East
Viking 1 Lander	22.27 North	312.03 East
Viking 2 Lander	47.67 North	134.48 East

How These Observations will be Made

It is anticipated that Surveyor's ground track will not pass 
directly over any of the targets so it will be necessary to rotate 
the spacecraft to sweep the field of view of its cameras across 
the targets as the spacecraft travels south from over the Martian 
north pole as the spacecraft gets closer and closer to the surface 
Photographs will be taken as long, narrow strips as the field of 
view is sweeping across the targets.

The orbital conditions chosen for the next five month period when 
Surveyor will not be aerobraking offer a particularly advantageous 
pattern of near overflights of these targets.  Because of the 
position of the targets in longitude around the planet (Viking 2 
is 182 degrees to the east of Viking 1, Mars Pathfinder is 14 
degrees to the east of Viking 1, and Cydonia is 24 degrees east of 
Viking 1) the near overflights will occur in clusters of five 
orbits every 17 orbits.  Surveyor's orbital period of 11.6 hours, 
which is slightly less half a Martian day, causes the spacecraft's 
ground track to alternate sides of the planet on consecutive 
revolutions.  At every closest approach to the planet or 
periapsis, the spacecraft is about 190 degrees to the east of 
where is was one orbit ago and about 20 degrees to the east of 
where it was two orbits ago.

These observations are termed "targeted" because mission 
controllers will take extraordinary steps to try to assure that 
the selected targets are within the high resolution camera's field 
of view.  This is a difference process than has been used in the 
past or will be used in the future to collect images of Mars from 
Global Surveyor.  The normal manner of acquiring images and other 
science data is to point the instruments straight down at the 
surface or to take science data as the instrument fields of view 
sweep across the planet as the spacecraft performs maneuvers to 
accomplish aerobraking.  During the aerobraking hiatus last Fall, 
the instruments were pointed straight down at the surface during 
the few minutes that the spacecraft was closest to the planet.  
During the two years of mapping that will start in March 1999, the 
instruments will always point straight down at the planet's 
surface.

The photographs that have been acquired during the just concluding 
aerobraking phase were acquired on each orbit, a few minutes after 
the closet approach to the planet's surface and after aerobraking 
had completed, as the spacecraft was being rotated from the 
aerobraking attitude to the array normal spin attitude used during 
the rest of each orbit.

Why are these Observations being Made Now?

Surveyor is just completing its first period of aerobraking--a 
portion of the mission in which the spacecraft skims through the 
top of the Martian atmosphere at each closest approach to the 
planet in order to circularize its orbit.  Currently, Surveyor's 
orbital period has been reduced from its initial 45 hour duration 
to under 12 hours.  The orbital period will stay at 11.6 hours 
until early September when aerobraking will resume again for the 
final five months of aerobraking to reach the exact orbital 
conditions necessary to begin Surveyor's two year long mapping 
mission.  During the period without aerobraking, Mars will move 
around the Sun to a position where the lighting of the Martian 
surface under Surveyor's flight path will be optimum for the 
mapping observations.

The upcoming opportunities appear to be the best of the period 
because the periapsis location will be migrating to higher 
latitudes and going over the north pole later in the period, and 
thus, the distance to the targets will be increasing.  In the next 
few weeks the elevation of the sun will be between 15 and 20 
degrees at the high latitude targets (Cydonia and Viking
2)	which will make for good imaging.  The sun elevation will be 
between 40 and 45 degrees for the low latitude sites (Viking 1 and 
Mars Pathfinder) which will make for acceptable imaging.

How Well will We be Able to See the Target in the Images?

For Example, the field of view of high resolution camera covers a 
width of 3 km (1.9 miles) when the camera is 400 km (249 miles) 
from its target.  The length of the image will be several 
kilometers (several miles).  The resolution, or smallest feature 
discernible in the image varies with the distance to the target, 
but at this distance will be approximately 1.4 meters (4.6 feet).  
The Mars Pathfinder and Viking landers are about 2 meters (6.6 
feet) in diameter, or very close to the minimum resolution 
obtainable.  The features in the Cydonia region are on the scale 
of 1 to 2 km (0.6 to1.2 miles) and should be readily visible and 
may nearly fill the width of field of view of the images.  Until 
the exact orbit characteristics are known, we will not know the 
exact distance to the targets.  It could be further than the 400 
km quoted in the example above and the resolution would be poorer, 
or it could be closer.

The Mars Pathfinder and Viking landers are very small targets, at 
the limit of resolution of the camera, even at the closest 
distance.  It will be an extraordinary event if they are 
recognized in the images.  Features in the Cydonia region, 
however, being hundreds to thousands of times larger, will be very 
easily seen, even at the more distant ranges, and while all 
features in this area may not be within the field of view due the 
expected targeting errors, there is a high probability that many 
will be seen with good resolution.  The best known location of the 
"Face" will be the target point in Cydonia.

What is the Probability that this Imaging will be Successful?  Or 
are We Sure We'll Get the Pictures?

The probability that the targets of interest will be within the 
camera's field of view varies between 30 and 50 percent.  This is 
because there are a number of sources of error or uncertainties 
associated with the targeting process.  One such error source 
relates to how good the current maps of Mars are.  As all early 
explorers on Earth found, early maps contain many inaccuracies.  
The data obtained by Surveyor's laser altimeter and cameras in the 
last few months have indicated that locations of observed objects 
on the surface are displaced 1 to 2 km (0.6 to 1.2 miles) from 
where the Viking era maps locate them.

Another source of error is the accuracy with which the 
spacecraft's trajectory is predictable.  This involves where the 
ground track of the flight path lies or will lie on the surface, 
and the time the spacecraft will fly over or near the desired 
targets.  The accurate prediction of the ground track allows the 
mission controllers to decide how much to rotate the spacecraft to 
point the camera, and the timing prediction will be used by the 
camera operators to control when to record the image.  In 
preparing the Surveyor's sequences for these observations, mission 
controllers will use the results of orbit computations made as 
near to the planned observation time as possible in order to 
minimize this uncertainty.  In addition, some error is introduced 
by the planet's rotation translating downtrack error into 
crosstrack error.

The last source of error is how accurately the spacecraft can be 
rotated and pointed.  The design specifications for Global 
Surveyor call for it to be pointable with an accuracy of 10 
milliradians ( 0.057 degrees), that is, mission controllers should 
be able to point the instruments to within 10 milliradians (0.057 
degrees) of a target.  Experience with the spacecraft indicates 
that it actually performs much better, and that a pointing 
accuracy of 3 milliradians (0.017 degrees) is possible.

Combining these error sources together in the proper statistical 
manner with the distance from the spacecraft to the targets tells 
us the probability that the targets will be within the camera's 
field of view.  This probability varies from about 70% when the 
targets are 1000 km (621 miles) from the spacecraft, to about 25% 
when the targets are 400 km (249 miles) from the spacecraft.

Why are these Images Important?

A great deal of scientific controversy rages over the 
interpretation of the features seen in the Viking images of the 
Cydonia Plain.  Additional photographs with the much better 
resolution that Surveyor's camera will provide and perhaps 
different lighting conditions can provide new information to aid 
in the understanding of what is seen there.  In addition, the 
observations of the previous landing sites provide scientists with 
important knowledge to tie together the observations made on the 
surface from the landers with those made from orbit above the 
planet.

The Viking 1 Lander site is the first location on Mars where 
humans were able to see and touch the Martian surface at a 
familiar scale.  This site, the following higher latitude Viking 2 
Lander site and the Pathfinder site play a large role in 
understanding the processes which have operated on the Martian 
surface over time and the state of the surface and atmosphere at 
present.  These sites serve as "ground truth" locations where 
ideas developed from orbital observations can be tested, verified 
and then extended to other regions of Mars such as those we may 
wish to visit in the future.

Several examples of this use of the sites for ground truth 
illustrates their significance.  One of the results of the Viking 
Orbiter Infrared Thermal Mapper experiment was a rock abundance 
map based on the observed change in surface temperature over time 
(large rocks cool more slowly than sand or dust).  The only way to 
verify the results of this rock abundance map was with the two 
Viking landing sites where, fortunately, numerous rocks were 
present.  Rock abundance knowledge helps in understanding the 
depositional history of the surface and large rocks represent a 
landing hazard.  Mars Global Surveyor carries an advanced version 
of the Viking instrument called the Thermal Emission Spectrometer 
(TES) which will be able to map rock abundance at more than one 
hundred times higher spatial resolution than Viking and the TES 
experimenters will have another site (Pathfinder) to use to verify 
their deductions.

The high resolution mode of the Mars Orbiter Camera (MOC) carried 
by the Mars Global Surveyor spacecraft is capable of returning 
images of objects as small as 1.4 meters across.  Some of the 
largest rocks in the area of the landing sites may be visible and 
such rock or boulder fields have been seen in MOC images at other 
locations on Mars.  The careful surveys which have been done of 
the distribution of rocks as a functions of rock size can now be 
used with MOC images to estimate rock populations at other 
locations on Mars.

The Current Status of Mars Global Surveyor

The Global Surveyor spacecraft is in excellent health.  For the 
next five months, Surveyor will be maintained in an 11.6 hour 
period elliptical orbit around Mars.  Its closest point to the 
planet's surface will be 170 km (106 miles) and its furthest 
distance will be 17,864 km (11,100 miles).

What's Next after these Special Observations?

The observations described above will occur three times during the 
month of April.  Surveyor will continue to acquire science data 
from its other instruments during the month.  Then, during May, 
Mars, and hence Global Surveyor will move behind the Sun as seen 
from Earth.  During this period of solar conjunction, 
communications with Surveyor will be greatly degraded.  Surveyor 
will cease science observations and will be put into a special 
attitude to assure proper temperatures of the science instruments.  
For two out of every eight hours it will point its high gain 
antenna to Earth to conduct radio communications propagation 
experiments, and, for part of the time, to allow mission 
controllers to monitor the spacecraft's health.  At the end of 
May, Surveyor will return to acquiring science data from all its 
instruments.
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THE "FACE ON MARS"
NASA release

25 March, 1998

Background:  The Viking Images

The Viking missions to Mars in the late 1970s produced more 
information about the Red Planet than had been gathered in all the 
previous centuries of study by Earth-bound astronomers and 
observers.  The primary mission of the Viking program was to 
search for signs of life on the surface of Mars.  Two landers 
containing sophisticated biological laboratories studied soil 
samples in a variety of tests which, it was hoped, would prove or 
disprove the existence of life.  The results of these tests 
indicated that Mars contained no life, at least at these landing 
sites.  However, Viking gathered volumes of data on the weather, 
soil chemistry and other surface properties and mapped the surface 
using low-to-moderate resolution cameras on the two orbiters.

Shortly after mapping began in 1976 an interesting image taken by 
the Viking 1 Orbiter was received at the Jet Propulsion 
Laboratory, Pasadena, Calif., which contained a surface feature 
resembling a human or ape-like face.  The photo was immediately 
released to the public as an interesting geological feature and 
dubbed the "Face on Mars." Shortly afterwards other photos of the 
same area were taken, and some scientists believed that the 
formation appeared to be a face due to the lighting angles as seen 
from the Orbiter.

Origin of Features Examined

Over the years, some people began to raise questions about the 
origins of the features.  A few ideas and theories arose 
speculating that the features may have been built by aliens in the 
distant past.  These theories are based largely on the results of 
computer photo enhancements and other analytical techniques 
performed on the Viking images beginning in the early 1980s.

Most planetary geologists familiar with the set of photos, 
however, concluded that the natural processes known to occur on 
Mars--such as wind erosion, Mars quakes, and erosion from running 
water in the distant past--could account for the formation of the 
complicated fretted terrain of the Cydonia region, including the 
face.

Because the entire data set includes only nine low-to-moderate 
resolution photos, scientists say that there just is not enough 
data available to justify what would be an extraordinary 
conclusion that the features are not natural in origin (many 
scientists question whether images alone would be enough to settle 
the matter).  Such a proven discovery of extraterrestrial life or 
artifacts would be one of the greatest discoveries in human 
history, and, as such, demand the most rigorous scientific 
investigation.

However, despite the phenomenal nature of such a potential 
discovery, no one in the scientific community--either in the U.S.  
or worldwide--has ever proposed an investigation for a mission to 
study these features.  Until more data is gathered, many 
scientists consider the probability that the features are anything 
other than natural in origin are just too low to justify the major 
expenditure of public funds which such an investigation would 
entail (more on this below).

What is agreed on is that a greater number of high resolution 
images of this area should be gathered.  Following the failure of 
the Mars Observer mission in August, 1993, NASA proposed a decade-
long program of Mars exploration, including orbiters and landers.  
The program, called Mars Surveyor, would take advantage of launch 
opportunities about every 2 years to launch an orbiter and a 
lander to the Red Planet.  The first mission, consisting of an 
orbiter to be launched in 1996, will map the surface and take 
high- and medium-resolution images of particular features on the 
Martian surface that are of high interest.  NASA intends to make 
observations of the Cydonia region making the best effort 
feasible, either with the first orbiter or on follow-on missions, 
to obtain images of the "face" and nearby landforms.

Quite aside from the interest generated by these curious features, 
Cydonia has long been regarded as an area of high scientific 
importance, ever since the first detailed images were returned by 
NASA's Viking spacecraft in the late 1970s.  The Cydonia region of 
Mars is part of the so-called fretted terrain, a belt of landforms 
that circles Mars at about 30-40 degrees North Latitude.  In this 
region, the ancient crust of Mars has been intensely eroded by 
weathering processes, leaving high remnants of older crust 
surrounded by lower plains of eroded debris.

The landforms of Cydonia resemble in some respects those of 
terrestrial deserts, but they probably have been shaped by a 
unique range of peculiarly martian agencies:  wind, frost and 
possibly running water in ancient times.  Deciphering the 
geological age and origin of this terrain will yield important 
insights into the evolution of the martian surface, into the role 
of ice and water in its development and into the nature of the 
martian climate in times past.

Proposing Investigations

The selection of goals and scientific priorities for NASA to 
undertake on future space science missions starts in the 
scientific and academic communities, as well as within NASA.  
Scientific associations, such as the National Academy of Science, 
determine the research priorities in any given field of science.  
For instance, the most important questions remaining about Mars 
include gaining an understanding of the amount of water on the 
planet; mapping the surface in detail to gain a complete 
understanding of the geological processes, history and 
composition; and gaining a global understanding of the atmosphere, 
including climate and weather.

When NASA receives permission to proceed with a science mission, 
the Agency publishes an Announcement of Opportunity (AO).  The AO 
solicits interest in providing high priority scientific 
investigations and instruments that will be part of the new 
mission.  The AO receives the widest possible circulation 
throughout the university and research communities and industry.

Proposals are submitted and reviewed through a competitive peer 
review process.  In this process, scientists from various 
institutions and organizations evaluate each proposal's scientific 
and technical merit, and then rank the relative merit of each.  
NASA receives the reports of the review panels and makes a final 
selection as to which instruments will be built and actually 
flown.  This rational selection process ensures that only the most 
useful research, with a high probability of returning good 
science, is done at taxpayer expense.

After selection, each Mars Surveyor Principle Investigator (PI) 
team will develop its instrument, build it, test it and prepare it 
for launch and the 10-month journey to Mars.  They are also 
charged with developing, testing, and using the software required 
to properly calibrate their instrument's data.  Most of the 
scientists working on the various Mars Surveyor missions will have 
several years invested in their instrument before the spacecraft 
arrives at Mars and they can actually receive the bulk of the data 
they have been waiting for.

Obtaining Images of the "Face" and Other Planetary Data

Since the release and subsequent widespread circulation of the 
'face' images, scientists and individual members of the public 
have freely drawn their own conclusions about the nature and 
origin of this feature.  NASA encourages anyone seriously 
interested in this topic to obtain the photo(s) and decide for 
themselves, just as every day many hundreds of independent 
researchers and scientists make use of NASA-provided data on a 
variety of subjects.

The most noteworthy image of the 'face' feature is available to 
the public, for a nominal fee, through Headquarters and JPL.  A 
photo catalogue can be provided to select images.

The phone numbers for ordering photos are:
HQ:  202/358-1900
JPL:  818/354-5011

All imaging data obtained by the Mars Surveyor program, as well as 
other types of data, will be deposited in open data archives.  Two 
such archives widely used are the Planetary Data System (PDS), an 
open archive accessible to thousands of scientists and other 
individuals, and the National Space Science Data Center (NSSDC) 
where images and other data will be readily available to the 
general public (generally on CD-ROMs or as hard copy, as 
appropriate), for a nominal charge that covers the materials and 
time needed to produce the copies.  For information about ordering 
copies of NASA science mission images, including on CD-ROM format, 
contact the NSSDC at:

National Space Science Data Center
Request Coordination Center
Goddard Space Flight Center
Greenbelt, MD 20771
Telephone:  301/286-6695
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1998 MARS SURVEYOR PROJECT STATUS REPORT
by John McNamee, Mars Surveyor 98 project manager

28 March, 1998

Orbiter and lander integration and test activities are proceeding 
on schedule with no significant problems. The orbiter spacecraft 
is being prepared for thermal vacuum testing scheduled to begin on 
April 8.  The lander spacecraft in full cruise configuration was 
transported to the acoustics lab at Lockheed Martin on March 21.  
Modal testing of the lander is scheduled to begin on March 30 and 
acoustic testing on April 3.  Final Orbiter-Lander UHF relay 
testing (uplink/downlink) was completed on March 27.
------------------------------------------------------------------

MARS SURVEYOR OPERATION PROJECT REPORT 
by Glenn Cunningham, Mars Global Surveyor project manager

27 March, 1998 

Early in the morning of March 27th, Mars Global Surveyor executed 
a 4.43 m/s bi-propellant main engine burn at the apoapsis of its 
201st orbit of Mars to raise its orbit's periapsis from 123 km to 
170 km and effectively terminate the first phase of aerobraking.

MGS will remain in this 11.6-hour duration orbit until early 
September 1998, when aerobraking operations will be undertaken 
again, further reducing the orbit period to the 2-hour, circular, 
sun synchronous mapping configuration.

The spacecraft was configured for this science phasing orbit 
period and the science instruments were turned on again later 
Friday morning.

During the five month period without aerobraking, MGS will return 
to taking science data with all its instruments.  At each 
periapsis passage, Mars Orbiter Camera images and Mars Orbiter 
Laser Altimeter measurements will be taken.  Magnetometer/Electron 
Reflectometer and Thermal Emission Spectrometer data will be taken 
all through the orbit period.  Radio science data will be taken at 
every opportunity.  X and Ka-Band propagation data will be 
acquired as the spacecraft approaches solar conjunction during 
May.

During April, MGS will have the opportunity to perform some 
"targeted" imaging of the Mars Pathfinder and Viking landing 
sites, as well as the Cydonia region.  There will be three 
opportunities on eight day centers to image each of the sites 
during April.  According to our previously announced process for 
imaging Cydonia, the Project has announced the opportunities 
(press release on March 26th), and will announce the detailed 
times of image acquisition and release early next week when 
updated orbit data is available.

The MGS spacecraft continues in excellent health.
------------------------------------------------------------------

RECENT SCIENTIFIC PAPERS ON ALH84001 EXPLAINED WITH INSIGHTFUL AND 
TOTALLY OBJECTIVE COMMENTARIES
by Allan Treiman, Lunar and Planetary Institute

Many scientific papers have now been published on the possibility 
that the martian meteorite ALH 84001 contains traces of ancient 
martian life (McKay et al. 1996a).  Many (probably most) of these 
papers are difficult to understand (even for specialists), and 
many do not really say why they are important.  Here, I've tried 
to present the main arguments of these papers for the educated 
nonspecialist, and some sense of why they are important (or why 
not).

The first paragraph(s) after the title are a quick summary of the 
results (or executive summary, or sound bite).  The more extended 
description follows.  Last are my insightful and totally objective 
commentaries, worth exactly what you paid for them.  My new year's 
resolution is to be more like Oscar the Grouch (of Sesame Street, 
if you've never had children).  The papers on ALH 84001 are given 
in reverse chronological order of publication date.

1] Jull A.J.T., Courtney C., Jeffrey D.A., and Beck J.W.  (1998) 
Isotopic evidence for a terrestrial source of organic compounds 
found in Martian meteorites Allan Hills 84001 and Elephant Moraine 
79001.  Science 279, 366-369.

Jull and co-workers measured the abundances of stable and 
radioactive isotopes of carbon in ALH 84001.  Most of carbon in 
ALH 84001 is from its carbonate mineral globules (as reported 
previously).  Most of the remaining carbon is from Earth organic 
material, i.e., terrestrial contamination.  A small fraction of 
the carbon (~8%) is too old to be Earth contamination, and is not 
(in chemistry and carbon isotopes) like carbon from the carbonate 
minerals.  This carbon may be from organic material formed on 
Mars, or possibly a rare inorganic mineral (also from Mars).

Part of McKay et al.'s (1996) argument for traces of martian life 
in ALH 84001 is that the meteorite contains organic material, rich 
in PAH compounds, associated with its carbonate mineral globules.  
However, Becker et al. (1996) argued that this organic material is 
actually terrestrial contamination.  To help resolve this issue, 
Jull and co-workers analyzed the isotopic composition of the 
carbon in the organic matter and the carbonate minerals of ALH 
84001 (following Jull et al., 1997).

The principal clue used by Jull is the abundance of the 
radioactive isotope of carbon, carbon-14, in the organic material.  
Carbon-14 is used as an age-dating tool for archaeological and 
cultural artifacts (like the Shroud of Turin).  Carbon-14 forms 
continuously and abundantly in the Earth's atmosphere.  As soon as 
a carbon-bearing compound is isolated from the atmosphere (e.g., a 
tree dies and stops absorbing CO2 from the air), its carbon-14 
starts decaying away with a half-life of 5730 years.  Most of the 
organic matter in ALH 84001 contains significant amounts of 
carbon-14--which means that it is terrestrial contamination (there 
is no reasonable extraterrestrial source of so much carbon-14).  
Also, the carbon-14 gives an average age near 6000 years, which is 
approximately 7000 years after ALH 84001 fell to Earth.  So, there 
is little doubt that most of the organic carbon in ALH 84001 is 
terrestrial contamination.  In addition, the relative abundances 
of carbon-12 and carbon-13 (the d 13C value) in the ALH 84001 
organics are typical or carbon from living things on Earth.

The carbon in carbonate minerals in ALH 84001 is clearly not 
terrestrial--it has little or no carbon-14, and a ?13C value much 
higher than typical of Earth carbonates.  Earlier, Jull et al.  
(1997) got similar results for carbonate minerals in a different 
sample of ALH 84001, although that sample had enough carbon-14 to 
suggest some chemical exchanges with Earth water.

However, a small part of the carbon in ALH 84001 might be martian 
organic material.  This carbon was not dissolved away during acid 
treatment designed to remove carbonate minerals, so it is either 
organic or some (unknown) resistant mineral.  This batch of carbon 
has no carbon-14, meaning that it is very old.  Jull and coworkers 
take this ancient age to mean that this batch of carbon did not 
form on Earth--it is martian.

This work appears to be carefully done, adequately documented, and 
carefully presented.  It does not directly refute McKay et al.'s 
(1996) hypothesis of martian biological activity in ALH 84001, but 
it is not much of a confirmation, either.  I have two comments 
about this work and possible evidence of martian biological 
activity in ALH 84001.

ALH 84001 contains hundreds of parts per million organic carbon, 
much more than other martian meteorites except EETA79001 (which 
Jull also analyzed in this paper).  This high abundance of organic 
matter has been used to support claims of fossil martian biology 
in ALH 84001.  However, ALH 84001 contains the same amount of 
organic carbon as do typical basalt meteorites from asteroids, 
even those found in Antarctica (Grady et al., 1997).  Just as Jull 
and co-workers showed that most of the organic carbon in ALH 84001 
is terrestrial contamination, Grady et al. (1997) showed that most 
of the carbon in asteroidal basalt meteorites is terrestrial 
contamination.  In this way, ALH 84001 is quite average and was 
not contaminated any more than normal for a meteorite.

The most intriguing part of Jull's work, at least to me, is the 
extraterrestrial organic (?) material they found in ALH 84001.  
They found this carbon in a sample of ALH 84001 that had been 
treated to remove all of its carbonate minerals.  At lower 
temperatures (<450C) this treated sample released the same 
terrestrial carbon (both 14C and ?13C) as the untreated sample.  But 
at higher temperatures, the treated sample released some carbon 
without any 14C, meaning it was pre-terrestrial.  This high-
temperature, non-carbonate carbon could be organic matter, or 
could possibly be a rare, acid-resistant, as-yet-unidentified 
inorganic mineral.  Many different kinds of organics can be 
released at these higher temperatures, including material like 
kerogen, graphite, and PAHs.  So, it is tempting to say that Jull 
and co-workers detected the same PAHs that McKay et al. found (and 
probably also other high-temperature organic compounds).  But most 
meteorite basalts from asteroids also contain about similar 
amounts of high-temperature carbon (10-30 parts per million; Grady 
et al. 1997).  Could it be that basalts in the solar system just 
have this much of high-temperature carbon compounds, whether or 
not life was present?

Citations:

Becker L., Glavin D.P., and Bada J.L.  (1997) Polycycic aromatic 
hydrocarbons (PAHs) in Antarctic Martian meteorites, carbonaceous 
chondrites, and polar ice.  Geochim. Cosmochim. Acta 61, 475-481.

Grady M.M., Wright I.P., and Pillinger C.T.  (1997) Carbon in 
howardite, eucrite, and diogenite basaltic achondrites.  
Meteoritics Planet. Sci. 32, 863-87

Jull A.J.T., Eastoe C.J., and Cloudt S.  (1997) Isotopic 
composition of carbonates in SNC meteorites, Allan Hills 84001 and 
Zagami.  Jour. Geophys. Res. 102, 1663-1669.


2] Bada, J.L., Glavin D.P., McDonald G.D., and Becker L.  (1998) A 
search for endogenous amino acids in martian meteorite ALH84001.  
Science 279, 362- 365.

Bada and co-workers analyzed ALH 84001 for amino acids, chemicals 
that are essential in life as-we-know-it on Earth.  In the 
meteorite's carbonate globules are small amounts of amino acids, 
which are nearly identical (in proportions of acid species and in 
their chemical handedness) to amino acids in Antarctic ice.  So, 
Bada and co-workers conclude that (essentially) all of the amino 
acids in ALH 84001 are terrestrial contamination, carried into the 
meteorite by melted Antarctic ice.

Part of McKay et al.'s (1996) argument for traces of martian life 
in ALH 84001 is that the meteorite contains organic material mixed 
with its carbonate mineral globules.  Last year, Bada's research 
group claimed the organic material is terrestrial contamination 
(Becker et al., 1996).  Continuing this work, Bada and co-workers 
analyzed ALH 84001 and its carbonate minerals for amino acids.  
Amino acids are small organic molecules, the building blocks of 
proteins and enzymes in all living things on Earth.  Earth life 
only uses a few of the many possible amino acids in fairly 
characteristic relative abundances, and only uses the L form of 
those amino acids.  With these distinctive characters, amino acids 
are a sensitive test for Earth organic contamination in 
meteorites.

To analyze for amino acids, Bada and co-workers used a very 
sensitive technique developed in their laboratory.  McKay et al.  
suggested that the signs of ancient martian life were associated 
with carbonate minerals in ALH 84001, so Bada and co-workers used 
a chemical extraction to separate amino acids in the carbonate 
globules from those elsewhere.  First, they rinsed the samples of 
ALH 84001 in distilled water, and that extracted no amino acids at 
all.  Then, they reacted the samples with weak hydrochloric acid, 
which should dissolve the carbonate minerals in the rock and 
release any amino acids associated with them.  This acid solution 
was dried, and part of it analyzed for free amino acids (those not 
chemically bound to anything else).  Another part of the solution 
was dried and treated to liberate amino acids that were bound to 
other molecules (for example, this treatment would break proteins 
into their constituent amino acids).  And finally, they analyzed 
the remainder of the meteorite that was not dissolved in acid 
(including the pyroxene and chromite mineral grains) for bound 
amino acids.

Bada and co-workers found that the amino acids in ALH 84001 were 
most abundant as bound acids associated with the carbonate 
minerals.  There were almost no amino acids in the distilled water 
wash, the acid-insoluble residue, or as free amino acids in the 
acid solution.  The part of ALH 84001 that dissolved in acid 
contained about 10 parts per million total amino acids (almost all 
chemically bound), while the rest of the rock contained only 75 - 
100 parts per billion of amino acids.

The amino acids in ALH 84001 are almost exactly in the same 
proportion as in the Antarctic ice--the proportions of DL-serine 
to glycine to L-alanine are approximately 3:3:1.  In addition, 
there is a little D-alanine in Antarctic ice and in ALH 84001 [ed. 
note:  possibly from micrometeorites in the ice?].  This 
similarity of terrestrial and ALH 84001 amino acids leaves little 
doubt that they are primarily terrestrial contamination, derived 
from amino acids in the ice that was around ALH 84001.

The amino acids that Bada and co-workers found in ALH 84001 are 
from the Antarctic ice.  But this fact is not a death-blow to the 
hypothesis of that ALH 84001 contains traces of ancient martian 
life (McKay et al. 1996).  Despite an exuberant press release from 
Scripps Oceanographic Institution, Bada's work is not a conclusive 
test of McKay's hypothesis.  McKay et al. (1996) did not talk 
about amino acids, so the absence of preterrestrial amino acids 
does not refute their hypothesis at all.  Of course, if Bada and 
co-workers had found abundant preterrestrial amino acids, it would 
have been strong support for McKay et al.'s hypothesis.

Two aspects of Bada's experiments are puzzling (although probably 
not very important).  First, their acid treatment was designed to 
dissolve carbonate minerals, but it dissolved 20% of their 
carbonate-free sample of lunar rock.  What actually dissolved from 
the lunar rock?  Possibly feldspar?  Could feldspar (or whatever) 
also have dissolved from ALH 84001, and would this change the 
conclusions?  Second, their acid treatment seems to have increased 
the masses of their samples.  For instance, sample 2 of ALH 84001 
started at 463 milligrams, and ended up as 472.5 milligrams (text 
and Table 1).  What is this extra mass?  Could it be lab 
contamination that might carry amino acids?

Citations:

Becker L., Glavin D.P., and Bada J.L.  (1997) Polycycic aromatic 
hydrocarb ons (PAHs) in Antarctic Martian meteorites, carbonaceous 
chondrites, and polar ice.  Geochim. Cosmochim. Acta 61, 475-481.


3a] Bradley J.P., Harvey R.P., and McSween H.Y.Jr.  (1997) No 
'nanofossils' in martian meteorite orthopyroxenite.  Nature 390, 
454.

3b] McKay D.S., Gibson E.K.Jr., Thomas-Keprta K., and Vali H.  
(1997) Reply to "No 'nanofossils' in martian meteorite 
orthopyroxenite." Nature 390, 455-456.

Bradley et al. claim that the possible nanofossils found by McKay 
et al. (1996) in martian meteorite ALH 84001 are actually 
irregularities in the surfaces of mineral grains.  These 
irregularities were accentuated by the metal coating that had to 
be put on the samples for electron microscope examination.  So, 
Bradley and co-workers reject the hypothesis that ALH 84001 
carries nanofossils of ancient martian life.

In response, McKay et al. say that they also found the same 
surface irregularities, and that they are not possible martian 
nanofossils.  The metal coating on the samples did not interfere 
with their identification of objects as nanofossils, because they 
did control experiments on metal coatings and know what the 
coating does.  (G.J. Taylor has posted a nice summary of these 
letters.)

Bradley and co-workers examined fracture surfaces of ALH 84001 
using nearly the same methods that McKay et al. (1996) used.  They 
found sausage-shaped surface features, approximately 100 to 400 
nanometers (billionths of a meter) long, that looked (to them) 
similar to the possible nanofossils in the McKay et al.  (1996) 
paper and in later magazine articles and press briefings.  Bradley 
found these sausage-shaped features on the carbonate minerals (as 
McKay's "nanofossils" were) and also on the host silicate 
minerals.  By observing the sample from many angles (in their 
electron microscope), Bradley found that the 'sausages' were not 
sitting on the host minerals, but were actually ridges poking out 
of the host minerals.

Bradley also did a few experiments on how the metal coating on the 
samples changes the shapes of surface features.  They found (as 
have others) that metal coatings tend to make surface features 
look segmented (the thicker, the more segmented) -- an appearance 
that McKay's group had suggested once to reflect cell boundaries.

McKay et al. respond that they have also seen ridges on minerals' 
surfaces that Bradley et al.  found--same sizes, shapes, and 
textures.  McKay and co-workers suggest that the ridges are grains 
of clay minerals formed during "incipient" alteration of the host 
minerals.  But these surface ridges, say McKay et al., are not the 
possible nanofossils they described in 1996 and subsequently.  
Their possible nanofossils differ from the Bradley ridges by not 
being parallel with each other, by intersecting with each other at 
distinct angles, by being curved, and by being rather isolated 
from each other.

McKay and colleagues also dispute that their identifications of 
possible nanofossils (here and earlier) were compromised by metal 
coatings on the samples.  They reiterate that they did control 
experiments on the effects of metal coatings, and that the 
nanofossil morphologies do not result from coating.  McKay also 
notes that some of Bradley's samples were coated with gold alone, 
rather than a gold-palladium alloy, and that gold coatings are 
known to make larger artifacts (artificial structures) than are 
gold-palladium.

This exchange focuses on two important issues about the possible 
martian nanofossils in ALH 84001:  1) how can you recognize a 
nanofossil, and 2) how does laboratory preparation change the 
surfaces of the samples.  Unfortunately, short "correspondence and 
reply" tidbits (Nature Nuggets) cannot carry enough scientific 
"meat" to resolve these issues.

1) How can you recognize that a shape in ALH 84001 is a martian 
nanofossil?  In 1996, McKay et al. cited "...regularly shaped 
ovoid and elongate forms ranging from 20 to 100 nanometers in 
longest dimension" as possible nanofossils (their Figure 6 and 
Kerr, 1996).  At their big NASA press conference, McKay and 
colleagues also presented an image of aligned sausage-shaped 
objects in a grid-formation as being possible nanofossils.  
Bradley et al. found features that matched these characteristics, 
and showed that they were not biological.

Here, McKay et al. seem to have changed their definition of 
martian nanofossils.  Nanofossils are still elongate and ovoid.  
Now, however:  they do not appear in parallel, but display 
"intersecting alignments;" they are relatively isolated from each 
other; they are significantly curved (their Fig. 2c); and they are 
much larger, up to 750 nanometers long.  With these new criteria, 
many of McKay's own objects may not qualify as nanofossils:  the 
ovoids of Figure 6a in McKay et al. (1996); the famous segmented 
worm shape (Kerr, 1996); and the aligned sausage-shaped objects.

2) How does the metal coating (for electron microscopy) affect the 
surfaces of minerals in ALH 84001?  This question has been argued, 
mostly in private, since McKay et al. (1996) was published.  In 
other words, are some of the "nanofossils" in ALH 84001 completely 
artificial, made during metal coating, and completely irrelevant 
to life on Mars?  Believable answers to these questions will only 
come from carefully controlled experiments, where fragments of ALH 
84001 are coated with various thicknesses of different metals and 
alloys.  Bradley et al. report that they did a few experiments in 
this program; McKay et al. report that they did a series of 
experiments on a different sample (a lunar glass).  Unfortunately, 
neither set of experiments has been reported in any detail, and I 
am still not sure of what metal coatings (Au or Au/Pd) do to 
surface morphology at these very small sizes.

Citations:

Kerr R.A.  (1996) Ancient life on Mars?  Science 273, 864-866.


4] Murty S.V.S.  and Mohapatra R.K.  (1997) Nitrogen and heavy 
noble gases in ALH 84001:  Signatures of ancient Martian 
atmosphere.  Geochim. Cosmochim. Acta 61, 5417-5428.

About 4.0 billion years ago, traces of noble gases and nitrogen 
from the martian atmosphere were trapped in ALH 84001.  The 
isotopic compositions and relative abundances of the heavy noble 
gases xenon (Xe) and krypton (Kr) are similar to the present-day 
martian atmosphere.  So, Mars unusual Xe and Kr compositions and 
abundances were set earlier than 4.0 billion years ago.  Argon 
trapped in ALH 84001 has less 40Ar from radioactive 40K (potassium) 
that Mars' present-day atmosphere, suggesting that it has 
continued to gain 40Ar over time [ed. note:  e.g., by volcanic 
outgassing].  Nitrogen trapped in ALH 84001 has much less of the 
heavy isotope 15N, consistent with loss of the light isotope 14N 
(and other light-weight gases) from Mars' atmosphere over the last 
4 billion years.

The elemental and isotopic composition of the martian atmosphere 
has been a real puzzle.  It is greatly depleted in the light 
stable isotopes of all gas elements, from hydrogen to xenon.  For 
instance, the abundance ratios of light to heavy xenon isotopes 
(e.g., 128Xe/136Xe) are approximately 0.7 times that in sun (Zahnle, 
1993).  It is a mystery how and when the light-weight isotopes 
were removed, but a separate process must have acted for each 
element (Pepin, 1994).  Any process strong enough to remove a lot 
of, say 128Xe compared to 136Xe, would certainly have removed all of 
the lighter gaseous elements completely (like krypton, argon, and 
nitrogen).  Similarly, any process capable of separating 36Ar from 
38Ar to the extent seen in the martian atmosphere would have 
removed essentially all of its nitrogen.

One way to help understand the martian atmosphere would be to 
learn how its composition has changed through time.  Its present-
day atmosphere (analyzed by Earth telescopes and the Viking 
landers) is the same as the atmosphere of 180 million years ago, 
as trapped in some martian meteorites (most notably EETA79001).  
Recognizing that ALH 84001 has retained noble gases (like argon) 
for 4.0 billion years, Murty and Mohapatra investigated whether it 
might contain trapped martian atmosphere from that time.  They 
used standard techniques--separating the meteorite into its 
minerals by their density, heating the samples up in steps of 
200C (or more) to 1600C, and collecting the gases given off by 
each sample in each temperature step.  The gases were separated, 
and the isotopic composition of each element was measured with a 
mass spectrometer.

Murty and Mohapatra found that ALH 84001 contains significant 
quantities of nitrogen, argon, krypton and xenon gases.  Most 
gases (xenon, krypton, nitrogen and 36Argon) all were released by 
the samples at nearly the same temperatures, suggesting that they 
are from the same trapped atmosphere component.  ALH 84001 
contains a nitrogen component comparable to Mars "mantle" (the 
Chassigny meteorite) and a trapped component with ?15N +85per mil; 
the current Mars atmosphere has d15N  +620 per mil.  From the 
isotopic composition of the argon (in mineral and temperature and 
temperature separates), the authors estimate that the trapped gas 
has 40Ar/36Ar of 1400, while the current Mars atmosphere has a value 
of 2400.  The trapped gas in ALH 84001 has 14N/36Ar about 60 times 
the value for the current Mars atmosphere.  The Kr and Xe isotope 
compositions of most of the trapped gas are similar to the current 
martian atmosphere, or current atmosphere as modified by 
groundwater processes.

Murty and Mohapatra infer that this trapped gas component is a 
sample of the martian atmosphere from 4.0 billion years ago, the 
age when argon gas was last lost from ALH 84001.  The ancient and 
modern atmospheres have similar isotopes and relative abundances 
of xenon and krypton (the heaviest noble gases), which means that 
the hydrodynamic escape processes that set these abundances 
(Pepin, 1994) were complete by 4.0 billion years ago.  The higher 
40Ar/36Ar in the current atmosphere reflects production of 40Ar from 
potassium over the history of Mars.  And the decrease in 14N/36Ar 
may reflect loss of nitrogen (through sputtering) into space over 
the last 4.0 billion years.

This work is not directly related to the "life in ALH 84001" 
folderol.  It is part of the long-term effort to learn about Mars' 
ancient environments through clues in the martian meteorites.  The 
noble gases and nitrogen hold great promise in unraveling the 
evolution of Mars' atmosphere, particularly why it is so thin now 
(surface pressure of ~1/200 that of Earth) and where its water has 
gone.  But this work, no matter how good, is not likely to be the 
final word from ALH 84001.  The uncertainty here is not from Murty 
and Mohapatra's analyses, but in the inherent variability of 
samples of ALH 84001 and the many assumptions that must be made to 
unravel the noble gas story.

First, it appears that different samples of ALH 84001 contain 
different quantities, proportions, and isotope compositions of the 
noble gases and nitrogen.  This is perhaps not too surprising, as 
the mineral proportions and chemical composition of ALH 84001 are 
rather variable, for instance potassium abundances (108 vs. 200 
parts per million:  Mittlefehldt, 1994; Dreibus et al., 1994).  
For the noble gases, this variability can appear as differences in 
the proportion of 40Ar that comes from radioactive potassium (this 
paper; Turner et al., 1997), and as differences in xenon isotope 
ratios (Fig. 9 of this paper vs. Fig. 2 of Swindle et al., 1995 
and Fig. 3 of Miura et al. 1995).  Variability like these in 
elemental and isotopic abundances suggests that the gases in ALH 
84001 came from many different sources and were not mixed well.  
It will be possible, eventually, to sort out the different sources 
(or components) of gas; now, it seems to be a muddle.

Second, interpretation of noble gas and nitrogen abundances is not 
simple, and relies on some (fairly complex) correction schemes and 
underlying assumptions.  Different research groups have not 
treated their data the same way; so when their results appear in 
conflict, it may be difficult for a non-specialist (like me) to 
understand why.  For instance, all groups so far have agreed that 
some of the argon in ALH 84001 comes from atmosphere trapped in 
the mineral grains.  Turner et al. (1997) present evidence that 
this trapped gas is like argon from the Earth's atmosphere:  
40Ar/36Ar = 295.  Murty and Mohapatra infer that the trapped argon 
is ancient martian, with 40Ar/36Ar = 1410.  Miura et al. (1995) and 
Goswami et al. (1997) use the current martian atmosphere value of 
40Ar/36Ar  2400.  Swindle et al. (1995) do not infer a specific 
40Ar/36Ar for the trapped component.  Is each group justified, given 
their data and the intrinsic variability of ALH 84001, or have 
some (or all) of them made unjustified simplifications in their 
data treatment?

Citations:

Dreibus G., Burghele A., Jochum K.P., Spettel B., Wlotzka F., and 
Wnke H.  (1994) Chemical and mineral composition of ALH 84001:  A 
martian orthopyroxenite (abstract).  Meteoritics 29, 461.

Goswami J.N., Sinha N., Murty S.V.S., Mohapatra R.K., and Clement 
C.J.  (1997) Nuclear tracks and light noble gases in Allan Hills 
84001:  Pre-atmospheric size, fall characteristics, cosmic ray 
exposure duration, and formation age.  Meteoritics Planet. Sci. 
32, 91-96.

Mittlefehldt D.W.  (1994) Errata.  Meteoritics 29, 900.

Miura Y.N., Nagao K., Sugiura N., Sagawa H., and Matsubara K.  
(1995) Orthopyroxenite ALH84001 and shergottite ALHA77005:  
Additional evidence for a martian origin from noble gases.  
Geochim. Cosmochim. Acta 59, 2105-2113.

Pepin R.O.  (1994) Evolution of the martian atmosphere.  Icarus 
111, 289-304.

Swindle T.D., Grier J.A., and Burkland M.K.  (1995) Noble gases in 
orthopyroxenite ALH84001:  A different kind of martian meteorite 
with an atmospheric signature.  Geochim. Cosmochim. Acta 59, 793-
801.

Turner G., Knott S.F., Ash R.D., and Gilmour J.D.  (1997) Ar-Ar 
chronology of the Martian meteorite ALH84001:  Evidence for the 
timing of the early bombardment of Mars.  Geochim. Cosmochim. Acta 
61, 3835-3850.

Zahnle K.J.  (1993) Xenonological constraints on the impact 
erosion of the early martian atmosphere.  Jour. Geophys. Res.  98, 
10899-10913.


5] Greenwood J.P., Riciputi L.R., and McSween H.Y.Jr.  (1997) 
Sulfide isotopic compositions in shergottites and ALH 84001, and 
possible implications for life on Mars.  Geochim. Cosmochim. Acta 
61, 4449-4453.

The authors measured the abundance ratio of sulfur isotopes 
(34S/32S) in minerals of martian meteorites to see if the sulfur in 
ALH 84001 had been processed by sulfate-reducing bacteria, as 
implied by McKay et al. (1996).  They found no evidence for the 
action of sulfate-reducing bacteria in ALH 84001, and so reject 
the McKay et al. (1996) hypothesis that ALH 84001 contains traces 
of ancient martian life.

The element sulfur occurs as two stable (not radioactive) isotopes 
with masses of 32 and 34, 32S and 34S.  Most sources of sulfur have 
abundance ratios of 34S/32S that are very similar to the average in 
the solar system.  However, sulfur that has been processed by 
bacteria (or other life forms) can have distinctly different 
abundances of these isotopes.  The greatest changes in S isotopes 
come from sulfate-reducing bacteria, which take sulfate ions (SO42-
) from water and convert them to sulfide ions (S2-) in water or as 
solid sulfide minerals.  Sulfate-reducing bacteria, when they have 
lots of sulfate in water around them, can form sulfide minerals 
with ~5% less 34S than the sulfate in the water.  This difference 
is easily detected, and has been used (on Earth) as a guide to the 
action of these bacteria.

To estimate the sulfur isotope ratio for bulk Mars, Greenwood et 
al. measured sulfur isotope ratios the martian basalt meteorites 
(Shergotty, Zagami, EETA79001, LEW88516, and QUE94201).  The 
sulfur isotope ratios for these meteorites are within 0.3% of the 
solar system average.  In ALH 84001, they first measured sulfur 
isotopes in millimeter-sized grains of pyrite (FeS2), which are 
not associated with the possible traces of ancient martian life 
(Gibson et al., 1996; but see Shearer et al., 1997).  The pyrite 
had variable and slightly "heavier" sulfur than the other martian 
meteorites, with 34S/32S from approximately 0.2 to 0.75% larger than 
the solar system average; this agrees with earlier work of Shearer 
et al. (1996).  Finally, they analyzed the sulfur-rich outer zone 
of a single carbonate globule from ALH 84001 iron sulfide minerals 
in the carbonate globules were claimed by McKay et al. (1996) to 
have formed through the action of martian biological organisms. 
The outer parts of the carbonate globules contain carbonate and 
oxide minerals in addition to the sulfides, so Greenwood et al.  
did not get so precise a result here as for the pure sulfide 
minerals.  Also, they had to apply a small correction for pairs of 
oxygen atoms masquerading as sulfur.  But the 34S/32S for the 
sulfide-rich region of the carbonate globule is identical to the 
non-biological pyrite in ALH 84001:  0.6% larger than the solar 
system average.

The non-biological and possibly biological sulfide minerals in ALH 
84001 have nearly identical 34S/32S ratios.  Greenwood et al.  take 
this similarity to suggest that sulfur (in the possibly biological 
sulfides) in the carbonate globules was not processed by sulfate-
reducing bacteria that the McKay et al. (1996) hypothesis is 
wrong.  Rather, they suggest that all the sulfides in ALH 84001 
formed from a high-temperature fluid (too hot for life-as-we-know-
it), probably generated by an asteroid impact onto Mars.  The 
variations in sulfur isotope ratios suggest mixing of "light" and 
"heavy" sulfur, the former perhaps from igneous rocks, the latter 
perhaps from Mars' surface.

This paper is much weaker than it could have been because the 
authors did not document their experiments adequately.  The 
analyses of sulfur isotopes in the pure sulfide minerals (pyrite 
and pyrrhotite) seem superb; they follow carefully described 
procedures, are based on good standards, and are repeatable.  But 
the analysis of sulfur isotopes in the carbonate globule, the 
critical analysis for evaluating the hypothesis of ancient martian 
life (McKay et al., 1996), will be suspect until Greenwood et al.  
document it fully.

The problem with Greenwood's analysis for sulfur isotopes in the 
carbonate globule is that they did not analyze only sulfide 
minerals.  Their instrument, an ion microprobe, shoots cesium ions 
at the sample, and collects ions from the sample that are 
sputtered off by the cesium.  Sulfur come off as S2- ions, both as 
the "light 32S2- and the "heavy" 34S2-.  Two problems are possible 
when the sulfur is present as sulfides among other minerals, like 
carbonates and oxides.

If the sulfide minerals are mixed with oxide and carbonate 
minerals, the ion 16O16O2- might be formed in abundance (from the 
carbonates and oxides) and might pass as 32S2-, as both ions have 
the same masses and charges.  If there were lots of 16O16O2- passing 
for 32S2-, the sulfur would appear "lighter" than it really is.

It is also possible that having sulfur-bearing minerals among 
other minerals influences the way that the sulfur sputters off the 
sample and into the analyzer.  For instance, sulfur in sulfides 
mixed with carbonates and oxides might sputter more like a sulfate 
than a sulfide, and require a different correction procedure.

Greenwood et al. were aware of these potential problems, and 
reported that they:  1) corrected for the presence of 16O16O2- (less 
than 0.2% in their value of 34S/32S); and 2) did experiments to show 
that their sulfur isotope correction procedures gave consistent 
results for 34S/32S with or without admixed carbonates and oxides.  
But they gave no details on the 16O16O2- correction, and no results 
for the experiments on mixtures.  Since we cannot see the details 
of their corrections, and the results of their experiments, we are 
really asked to take on faith that Greenwood did both properly.  
Some scientists, trusting the authors implicitly, will take their 
work on faith.  Others, who do not accept the conclusions of 
Greenwood et al., will point to these problems as cause for 
discounting the paper entirely.  And those who wish to "trust, but 
verify" will merely be disappointed.

Citations:

Gibson E.K.Jr., McKay D.S., Thomas-Keprta K.L., and Romanek C.S.  
(1996) Evaluating the evidence for past life on Mars (letter).  
Science 274 , 2125.

Shearer C.K., Layne G.D., Papike J.J., and Spilde M.N.  (1996) 
Sulfur isotope systematics in alteration assemblages in martian 
meteorite ALH 84001.  Geochim. Cosmochim. Acta 60, 2921-2926.

Shearer C.K., Spilde M.N., Wiedenbeck M., and Papike J.J.  (1997) 
The petrogenetic relationship between carbonates and pyrite in 
martian meteorite ALH 84001 (abstract).  Lunar Planet. Sci. 
XXVIII, 1293 -1294.


6] Turner G., Knott S.F., Ash R.D., and Gilmour J.D.  (1997) Ar-Ar 
chronology of the martian meteorite ALH 84001:  Evidence for the 
timing of the early bombardment of Mars.  Geochim. Cosmochim. Acta 
61, 3835-3850.

The authors studied the age of ALH 84001, using 39Ar-40Ar (argon-
argon) radio-isotope dating.  For the "traces of ancient life" 
controversy, their most important result is a revision of the 3.6 
billion-year-old age that McKay et al. (1996) used as the time of 
carbonate formation.  Turner et al. have revised the age for this 
particular sample of carbonate to 3.83  0.15 billion years, 
within uncertainty of nearly all other 39Ar-40Ar ages for ALH 84001.  
This "carbonate" age may not be when the carbonates formed.  It 
actually is the age of the feldspar-composition glass that is 
mixed with the carbonate minerals, which could be older, younger, 
or the same as the carbonates.

This paper represents an exhaustive study of the 39Ar-40Ar age of 
ALH 84001; this radioactive age-dating system is actually the 
potassium-argon (K-Ar) system, but some of the potassium is 
converted to 39Ar (in a nuclear reactor) so it can be measured at 
the same time as the 40Ar.  Also, Turner and coworkers calculated 
the cosmic ray exposure age of ALH 84001 and its abundance of 
trapped martian atmosphere.  Turner et al. studied three rock 
fragments by "stepped heating:"  heating each sample up 100C at a 
time and collecting all the argon that was released at each 
temperature.  This method allowed them to tell what abundances of 
argon isotopes were released by each kind of mineral in the 
fragment.  Turner et al. also analyzed 40 spots on thin sections 
(microscope slides) by vaporizing them with a laser beam and 
collecting the argon that was released.

After corrections for various sources of argon, including 
contamination from martian atmosphere, Turner et al. found that 
nearly all of the samples were consistent with an 39Ar-40Ar age of 
3.97 billion years, possibly as old as 4.05 billion or as young as 
3.8 billion.  This 39Ar-40Ar age for ALH 84001 is essentially the 
same as determined by other research labs (Bogard and Garrison, 
1997; Goswami et al., 1997).  Two samples gave older ages, near 
4.4 billion years; its is not clear if these ages are real.

The age of sample 110i, rich in carbonate minerals, was originally 
reported as 3.6 billion years (Knott et al., 1996); McKay et al.  
(1996) took that as the age of the carbonate globules and their 
possible signs of Martian life in ALH 84001.  This ancient age was 
important, as it placed the possible signs of martian life in the 
distant past, when Mars was probably much wetter (and possibly 
much warmer) than it is now.  This ancient "warm, wet" Mars would 
have been similar to the ancient Earth, and so a reasonable place 
for life to form and flourish.

However, Turner et al.  have revised the age of sample 110i to 
3.83  0.15 billion years, which is (within uncertainty) the same 
as nearly all other 39Ar-40Ar ages for ALH 84001.  Further, sample 
110i contains a LOT of potassium, much more than could have come 
from the carbonate minerals alone.  The potassium in 110i probably 
came from silicate glass (like maskelynite) mixed with the 
carbonate, and so its 39Ar-40Ar age is the formation (or last 
heating event) of the silicate glass!  So the age of spot 110i 
really does not limit the age when the carbonate formed.

In calculating the 39Ar-40Ar ages of their samples, Turner et al. 
had to determine the proportion of Earth and martian atmospheres 
in their samples, and also how long the samples were exposed to 
cosmic rays in interplanetary space.  Some samples had significant 
proportions of Earth atmosphere, but most had relatively little 
martian atmosphere.  On average, less than 5% of the 40Ar in the 
samples came from the present-day martian atmosphere; this 40Ar 
probably was forced into the glass in ALH 84001 when it was 
ejected from Mars.  That probably happened approximately 14 
million years ago, the cosmic ray exposure age (see the paper 
below by Eugster et al., 1997).

The 39Ar-40Ar age of approximately 4.0 billion years fits well with 
the ages of planetary bodies in the solar system.  Most rocks from 
the Moon's highlands give 39Ar-40Ar ages from 3.8 to 4.0 billion; 
the oldest rocks on Earth formed at about 4.0 billion; many 
meteorites were shocked by impact between 4.1 and 3.5 billion 
years ago.  Turner et al. suggest that the 39Ar-40Ar age of ALH 
84001 represents an asteroid impact onto Mars (Treiman, 1995), and 
that impact was approximately at the same time as the large impact 
basins formed on the Moon.  This correspondence seems to support 
the idea of a "lunar cataclysm" at about 4.0 billion years ago--a 
time when the Moon's surface was especially hard hit by asteroids.

This paper was submitted for publication in August, 1996, back 
when ALH 84001 was most interesting as a sample of the ancient 
Martian crust.  That was the impetus for this study--G. Turner and 
his group wanted to understand the age and impact history Mars, 
especially as it might relate to the Moon.  Ar-Ar ages for moon 
rocks cluster at 4.1 to 3.8 billion years ago, which suggests to 
some people that this was a time of abundant large asteroid 
impacts on the Moon--the so-called "lunar cataclysm."  Other 
people have concluded that the Moon was hammered by asteroid 
collisions continuously from 4.5 billion years ago through 3.8 
billion, but that older ages were erased by younger ones.  The 
results here seem consistent with the notion of an impact 
"cataclysm" happening throughout the inner solar system.

For this study, Turner and colleagues had to know which event was 
actually being dated by the Ar-Ar system, they accepted Treiman's 
(1995) history as best fitting their data.  Treiman (1995) 
proposed that ALH 84001 experienced two shock events:  one that 
granulated and sheared the rock, and a second (after the carbonate 
globules formed) that produced shock glass with little 
deformation.  Turner et al. assigned their age to the earlier 
event, and noted that production of shock glasses commonly does 
not reset Ar-Ar ages.

However, Turner et al. did not consider more recent, alternate 
histories for ALH 84001; they were proposed after this paper was 
written.  Bradley et al.  (1996, 1997) gave evidence that ALH 
84001 was heated to above 500C during formation of some magnetite 
grains, and (they infer) during formation of the carbonate 
globules.  Scott et al. (1997) inferred that the carbonate 
globules and the feldspar-composition glass formed simultaneously 
in a single shock event.  If either of these scenarios were true, 
they would most likely be recorded by the Ar-Ar age dates and 
could have happened 4.0 billion years ago.


7] Gleason J.D., Kring D.A., Hill D.H., and Boynton W.V.  (1997) 
Petrography and bulk chemistry of Martian orthopyroxenite ALH 
84001:  Implications for the origin of secondary carbonates.  
Geochim. Cosmochim. Acta 61, 3503-3512.

Gleason and coworkers did a general study of ALH 84001, 
emphasizing microscope observations and chemical compositions of 
the rock and its minerals.  Particularly, they examined the 
carbonate globules which McKay et al. (1996) suggested were formed 
by ancient martian life.  Gleason and coworkers infer that the 
globules were deposited from liquid water, and so disagree with 
Harvey and McSween (1996) and Scott et al. (1997), who claimed 
that the carbonate minerals formed at high temperatures from 
molten carbonates.

However, Gleason saw no evidence that the carbonate globules were 
associated with life, and so do not support McKay et al. (1996).  
On the contrary, they noted that similar carbonate globules have 
formed in other meteorites and on Earth without any apparent 
biological influences.

Gleason and coworkers inferred, from mineral textures, that the 
carbonate globules grew from water-rich fluid cooler that 300C.  
The carbonate globules appear to have formed by replacing material 
with the composition of plagioclase feldspar.  Treiman (1995) had 
inferred that this material was crystalline feldspar, but Gleason 
noted that carbonate replacing crystalline feldspar grows as crack 
filling and veinlets, not as globules.  So they conclude that the 
carbonates in ALH 84001 replaced feldspar glass, not crystals.  If 
the feldspar glass ever been hotter than 300C for a few hours 
even, it would have crystallized back to plagioclase again.  
Gleason inferred that the this feldspar glass formed at the same 
time as did the granular bands (crush zones) that criss-cross the 
meteorite.

Gleason and co-workers also observed is that the chemical 
composition of ALH 84001 varies a bit.  They analyzed the chemical 
composition of two 1/3-gram fragments from different parts of ALH 
84001.  Some elements (like lanthanum) are five times less 
abundant in the fragment from a "crush zone" than the other 
fragment.  Similar variability is apparent in other published 
chemical analyses.  Gleason thinks this variability arose as some 
elements (like lanthanum) moved around in ALH 84001 before the 
carbonate globules grew.

Finally, Gleason noted that pyrite, an iron sulfide mineral, was 
associated with chromite.  They did not mention finding any 
pyrrhotite, another iron sulfide mineral.  The significance of 
these observations is discussed below.

Gleason and co-workers have provided a wealth of new chemical data 
on ALH 84001, and their excellent microscope observations 
(although important) do not resolve the issue of ancient life in 
ALH 84001.  Rather, their work serves to emphasize the depth of 
disagreement about ALH 84001, and how much remains to be learned 
about the rock.

As for the carbonate globules, Gleason and co-workers support the 
low-temperature position of Romanek et al. (1994), Treiman (1995) 
and Valley et al. (1997); low-temperature here means < 300C, 
which could still be much too hot for life as we know it.  Gleason 
sees no evidence for the very high temperatures (> 500C) inferred 
by Harvey and McSween (1996), Bradley et al. (1996), and Scott et 
al. (1997).  Gleason and co-workers do not have proof that the 
carbonates formed without life, just their reasoned judgment that 
life is not absolutely required to produce the structures and 
compositions they found.

Their inference that the carbonate globules replaced glass rather 
than crystalline plagioclase is intriguing, and seems to be more 
realistic than my 1995 suggestion that the carbonates replaced 
crystalline plagioclase.  However, there is no general agreement 
on how the carbonate globules formed; others have claimed that 
they replace pyroxenes or that they filled cracks and bubbles in 
the rock.

The variability of the chemical composition of ALH 84001 is not 
surprising.  ALH formed when crystals of the mineral orthopyroxene 
grew in a mass of basalt magma, and settled out to the bottom of 
the mass.  Elements like lanthanum would have been concentrated in 
the magma among the settled crystals.  So the amount of lanthanum 
in a piece of ALH 84001 would represent how much magma was caught 
among the orthopyroxene crystals.  And the amount of magma might 
vary simply because the crystals were packed together tighter is 
some spots.  On the other hand, the low-lanthanum sample is from a 
`crushed zone', and it is possible that the crushing managed to 
squeeze some lanthanum-bearing mineral (like plagioclase glass) 
out of that area.

Finally, the observations here remind us of problems with the 
sulfide minerals in ALH 84001.  First, Gleason and coworkers found 
pyrite (FeS2) associated with chromite rather than with the 
carbonate globules as reported by most other workers.  The 
chromite has nothing to do with the hypothesis of fossil life in 
ALH 84001, while (of course) the carbonate globules do.  Now, the 
sulfur isotope ratio (34S/32S) in the pyrite does not look those in 
Earth life, and so seemed to mean that the carbonate globules 
could not be associated with life (Shearer et al., 1996; Greenwood 
et al., 1997; Shearer, 1997; Shearer and Papike, 1996, 1997).  
However, if the pyrite did not form with the carbonate globules, 
its sulfur isotope ratio is not relevant to the hypothesis of 
life.  Second, Gleason and co-workers did not mention finding any 
pyrrhotite (Fe1-xS) in ALH 84001; in fact, no pyrrhotite has been 
seen in thin sections.  This absence is peculiar, as Kirschvink et 
al (1997) found that the magnetism in ALH 84001 was trapped in 
pyrrhotite!  Where is the pyrrhotite, or could the magnetic 
signature be from some other mineral?


8] Eugster O., Weigel A., and Polnau E.  (1997) Ejection times of 
Martian meteorites.  Geochim. Cosmochim. Acta 61, 2749-2757.

The authors used abundances of "cosmogenic nuclides," produced 
when a meteorite is exposed to cosmic rays, to measure how long 
four martian meteorites were in interplanetary space.  ALH 84001 
was exposed to cosmic rays for 14.4  0.7 million years, which 
probably is the time when ALH 84001 was blasted off Mars.  This 
cosmic ray exposure age for ALH 84001 is similar to ages found by 
other researchers (e.g., Goswami et al., 1997).  None of the other 
martian meteorites were exposed in interplanetary space for so 
long, so it seems fairly certain that ALH 84001 did not come from 
the same site on Mars (impact crater on Mars) as any other martian 
meteorite.


9] Hutchins K.S. and Jakosky B.M.  (1997) Carbonates in martian 
meteorite ALH84001:  A planetary perspective on formation 
temperature.  Geophys. Res. Lett. 24, 819-822.

The possible traces of life in ALH 84001 are all associated with 
its carbonate mineral globules, and so the formation of the 
globules is very important.  If the globules formed was hotter 
than about 150C, a biological origin seems quite unlikely.  Low 
formation temperatures, less than 80C, have been derived from the 
abundances of oxygen isotopes (16O and 18O) in the carbonates by 
Romanek et al. (1994).

Here, Hutchins and Jakosky suggest that Romanek et al.s 
temperature estimate was too low.  Romanek et al. used oxygen 
isotope ratios as a thermometer, by comparing the oxygen isotope 
ratios (18O/16O) of a mineral and the liquid it grew from.  The 
greater the difference in 18O/16O between the mineral and liquid, 
the lower the temperature would have been.  None of the liquid is 
trapped in ALH 84001, so Romanek et al. had to estimate its oxygen 
isotope ratio as something like normal waters on Earth.  Hutchins 
and Jakosky point out that oxygen and carbon in the martian 
atmosphere are much richer heavy isotopes of oxygen and carbon (18O 
and 13C) than in the Earths atmosphere, and so Mars' water is also 
likely to have a relatively high 18O/16O and 13C/12C ratios.  When 
put into the oxygen isotope thermometer, this difference means 
that the ALH 84001 carbonates probably formed between 40C and 
250C.

This paper emphasizes yet another uncertainty in determining the 
temperature of formation of the carbonate globules in ALH 84001.  
Whether Romanek et al. or Hutchins and Jakosky are more correct 
depends on two questions.

First, did Mars' atmosphere have its current high 18O/16O and 13C/12C 
ratio before the carbonates formed?  If not, Hutchins and 
Jakosky's argument is not valid.  Today, Mars' atmosphere has a 
significantly higher 18O/16O and 13C/12C than martian rocks (the 
meteorites), and this difference means that the atmosphere somehow 
lost much of its original 16O and 12C to space.  How the atmosphere 
lost these light isotopes is not certain, but Mars' low gravity 
(compared to Earth) and weaker magnetic field were probably 
important.  When the light isotopes left Mars' atmosphere is not 
known (Jakosky and Jones, 1997); unfortunately, when the 
carbonates were deposited is not really known either.

Second, did the liquid that deposited the carbonates come 
(eventually) from Mars' atmosphere?  Hutchins and Jakosky's paper 
works from the idea that the liquid came from the atmosphere, and 
shared its high 18O/16O and 13C/12C ratios.  But it is possible that 
the liquid came from deep inside Mars (in the jargon, "juvenile 
water"), and never contacted the atmosphere.  In that case, the 
high 18O/16O and 13C/12C of the ALH 84001 carbonates came entirely 
from a low formation temperature.


10] Scott E.R.D., Yamaguchi A. and Krot A.N.  (1997) Petrological 
evidence for shock melting of carbonates in the martian meteorite 
ALH84001.  Nature 387, 366-379.

Here's a new theory of the origin of the carbonate globules in ALH 
84001:  they formed at very high temperature, during an asteroid 
impact on Mars, from carbonate rich melt.  If the globules formed 
this way, they could not have been hosts to ancient martian life 
forms (McKay et al., 1996).

The authors' argument is in four parts:  1) the clear silicate 
glass in ALH 84001 was melted during an impact shock (presumably 
an asteroid hitting Mars); 2) all the shock features in ALH 84001 
formed in this same shock event; 3) the small dispersed grains of 
carbonate minerals were once molten, like the glass, because they 
all share similar structures and textures; and 4) and the 
structures and textures of the large carbonate globules also fit 
with once being molten.

First, the authors show that the clear glass was once molten, a 
liquid.  This glass had been called "maskelynite," which forms 
from feldspar minerals during shock without melting.  The authors 
here show that the glass was molten because:  its shapes were 
modified by shock, veinlets of the glass were injected into other 
minerals, it contains flow features, and it contains bubbles.  
Further, the chemical composition of the glass is not just the 
same as feldspar minerals; in addition to feldspar, the glass 
contains extra silica and sometimes extra chromium (from the 
mineral chromite).  [The authors do not give a melting 
temperature, but it was much more than 1000C!]

Second, the authors suggest that all the shock features in ALH 
84001 formed in the same shock event that melted the glass.  They 
note that single impact events can produce lots of different shock 
effects in a single rock, and the effects can cut across each 
other.  They infer that the "crush zones" or granular bands that 
criss-cross the rock were the first shock effect, and that the 
glass formed next [probably within seconds or a minute].

Third, the authors see that the glass and the small carbonate 
grains have similar shapes, and infer that both formed in the same 
way.  The glass and small carbonates both enclose pyroxene grains 
in rounded shapes, and fill cracks in grains.  Some cracks contain 
both carbonate minerals and the glass, which suggests to the 
authors that the cracks (and the "crush zones") formed at the same 
time as both the glass and the carbonates.  So, the authors 
suggest that the glass and the carbonate melted at the same time 
and squirted into and around other minerals in ALH 84001.  
Carbonate melts are very runny, so they would squirt more easily 
into cracks; there is more carbonate than glass in the cracks.  
The authors looked for evidence in support of other proposed 
origins for the carbonates, and found none to their satisfaction.

Fourth, the authors demonstrate that the carbonate globules could 
have formed as melt droplets, just like the small carbonate 
grains.  The small carbonate grains cover the same range of 
chemical compositions as the large grains, suggesting that they 
formed at the same time in the same process (as impact melts).  
The shapes of the globules in the glass are like liquids that 
don't mix (like oil droplets in water); carbonate melts do not mix 
with silica-rich melts, and can form rounded shapes like the 
globules in ALH 84001.  The authors also cite cases on Earth where 
carbonate minerals have been melted and moved around during impact 
shocks.

So, all the carbonates now in ALH 84001 formed at very high 
temperatures.  This theory is completely inconsistent with the 
inferences of McKay et al. (1996) that the carbonate globules 
contain evidence for martian life.  ALH 84001 must have contained 
carbonate minerals before they were shock melted, but the origin 
of these ancestral carbonates is not known.

In my opinion, this paper does not refute McKay et al. (1996), 
because it doesn't prove that the carbonate globules formed at a 
high temperature.  The actual observations here are new and 
convincing, and it seems certain that that the clear glasses in 
ALH 84001 were once molten.  There remain (to me) some stumbling 
blocks between this conclusion and the claim that all the 
carbonate globules formed at the same high temperature as the 
clear glass.

The biggest doubt is whether the carbonate globules were ever 
molten, whether they actually were rapidly cooled droplets of 
carbonate melt.  These observations, among others, seem difficult 
to explain if the carbonate globules were once molten.

* The mineral grains in each carbonate globule grew outward toward 
the globule's rim.  However, crystals growing from a melt globule 
will usually grow inward from the rim because melts crystallize as 
they cool down, and the rim of a globule is its first part to cool 
(like Fig. 15.6b of Kjarsgaard and Hamilton, 1989).

* The carbonate globules have different chemical compositions 
inside and out (from brownish cores rich in calcium and iron to 
water-clear rims rich in magnesium).  This zoning is unlikely from 
carbonate melt globules in two ways.  If the globules cooled 
really fast, they ought to have little zoning because the calcium, 
iron and magnesium in the melt would grow into the crystals before 
the magnesium had time to separate from the calcium and iron.  On 
the other hand, if cooling were slow enough that the calcium, 
iron, and magnesium in the melt could move around, the solidified 
globules ought to be zoned the other way:  cores rich in magnesium 
and rims rich in calcium and iron (Scott et al. mention this 
problem).

There are other problems here too, and they will be explored at 
length.  First, the evidence that all the shock features in ALH 
84001 formed in a single impact event is not (to me) very 
convincing, compared to evidence for multiple impacts (Treiman, 
1995).  Second, McKay and Lofgren (1996) showed a picture of a the 
glass cutting across the Ca-Fe-Mg layering and "oreo cookie" rim 
of a carbonate globule.  This structure seems difficult to make if 
the glass and carbonate were liquid at the same time.  And third, 
the zoning in oxygen isotopes from core to rim in the globules 
(Valley et al., 1997; Leshin et al., 1997; Saxton et al., 1997) 
may be impossible to produce at the high temperatures needed to 
melt these carbonates.

For more about this paper, check out the University of Hawaii's 
Planetary Science Research Discoveries webzine.


11] Kirschvink, J.L., Maine A.T., and Vali H.  (1997) 
Paleomagnetic evidence of a low-temperature origin of carbonate in 
the martian meteorite ALH 84001.  Science, 275, 1629-1633.

When a rock forms or cools down, it can trap some of the local 
magnetic field; magnetic minerals in the rock become little bar 
magnets, aligned with the planet's magnetic field.  This trapped 
magnetic field, called natural remnant magnetism or NRM, can stay 
in the rock indefinitely, and can be used to unravel the history 
of the magnetic minerals and the rock.  The strength of the 
trapped magnetic field can tell how strong the planet's field was.  
If the rock is broken or bent, the magnetic field trapped in it 
will point in a different direction from the original field.  If 
the rock gets heated above a critical temperature, the old trapped 
magnetic field is lost, and a new one is trapped when it cools 
down again.

For the McKay et al. (1996) hypothesis of fossil martian life in 
ALH 84001, the most important result from Kirschvink et al. is 
that the carbonate globules formed below 325C, and probably below 
~110C.  McKay et al. require a low formation temperature to 
permit bacterial growth, and many types of Earth bacteria and 
archaea can live and prosper at 110C!  The upper temperature 
limit is too high for known Earth life, but is an upper limit, and 
is still better for McKay et al. than the 500-700C temperatures 
estimated by other groups.

The argument for carbonate formation below 325C is indirect, but 
fairly clear.  Kirschvink et al. measured the trapped magnetic 
fields (NRM) in two adjacent fragments of ALH 84001 from the 
fracture zone where McKay et al. found the most carbonate 
globules.  The trapped fields in the two fragments were strong, 
equally strong, but in different orientations; the "bar-magnets" 
of the magnetic minerals were pointed in different directions.  
This meant that the two fragments had probably trapped the same 
original field, but had been rotated or jostled when the fracture 
between them formed.  If ALH 84001 had ever been hotter than 325C 
since the fragments were jostled, they would have lost their 
original magnetic fields; when they cooled, the fragments would 
have trapped the new magnetic field, with the same direction in 
both fragments! Because the fragments do have magnetic fields in 
different directions, ALH 84001 could not have been hotter that 
325C at any time after the fractures formed.  Now, the carbonate 
globules are in these same fractures, and must have formed after 
the fractures did, and so must not have formed at temperatures 
hotter than 325C (otherwise the rock fragments would have their 
trapped magnetic fields pointing in the same direction)!

The argument for carbonate formation below ~110C depends on the 
details of how the trapped magnetic field changes as the rock is 
heated.  In ALH 84001, the trapped magnetic field is in the iron 
sulfide mineral pyrrhotite.  When pyrrhotite is heated to 
temperatures below its critical temperature of 325C, its trapped 
magnetic field fades away somewhat.  But Kirschvink et al.  found 
no hint of this fading in ALH 84001's trapped magnetic field.  The 
110C temperature actually comes from their sample preparation, 
not anything inside the rock.  They had to heat their samples to 
110C to allow their glue to cure.  If ALH 84001 had been heated 
to >110C on Mars, any magnetic effects would have been erased as 
the glue cured.

The results of this paper are a strong challenge to "anti-life in 
ALH 84001" scientists.  However, the results are not (yet) proof 
of a low-temperature origin and certainly not proof of life on 
Mars.  Although I am not an expert on magnetism, I see two issues 
in this work as it relates to McKay et al.'s hypothesis that ALH 
84001 contains traces of ancient martian life.

The first issue is the timing of fracturing of ALH 84001 compared 
to the timing of carbonate formation.  ALH 84001 was fractured at 
least twice, before and after the carbonate globules formed.  Many 
carbonate globules sit in fractures, so these fractures must have 
been there first (McKay et al., 1996).  The carbonate globules are 
themselves sliced and broken along fractures, which must have come 
later (Mittlefehldt, 1994; Treiman, 1995; McKay et al., 1997).  
So, could Kirschvink's two rock fragments have separated by a late 
fracture, rather than an early fracture?  If this particular 
fracture formed after the carbonate globules were deposited, 
Kirschvink's results here would say nothing about formation of the 
carbonate globules.

The second issue is the absolute age of the carbonate globules, 
which should be ancient (3.6 billion years old) according to McKay 
et al. (1996).  The problem here is that the tiny magnetite grains 
in the carbonate globules have not trapped any detectable magnetic 
field themselves.  The magnetites do contribute to other magnetic 
properties of the rock, just not the trapped field (the NRM).  
Could this mean that the magnetite grains grew when there was no 
field, and so are fairly young (Wadhwa and Lugmair, 1996)?  Or 
could it mean that Kirschvink's sample had so few carbonate 
globules that their trapped magnetic field could not be detected?

The most important result from this paper, particularly for life 
on Mars, is the evidence that Mars had a strong magnetic field!  
Mars now has no detectable magnetic field, and had hardly any 
field 1.3 billion years ago, when many of the martian meteorites 
formed.  Kirschvink et al.  have demonstrated that Mars had a 
strong magnetic field (possibly as strong as the Earth's is now) 
about 4.0 billion years ago, when ALH 84001 cooled.

First, a strong magnetic field would have protected Mars' surface 
from much deadly radiation from space.  Its magnetic field would 
have deflected radiation like electrons and protons from the Sun, 
just as the Earth's magnetic field protects us now.

Second, and perhaps more important, a magnetic field early in 
Mars' history would have protected its atmosphere.  Mars' 
atmosphere is now quite thin, about 1/200 as thick as the Earth's.  
Without a thick atmosphere, Mars' surface could never have been 
warm enough to permit liquid water, and there is very good 
geologic evidence that liquid water was once abundant on the 
surface of Mars.  What happened to Mars' atmosphere?  Much of it 
was swept away by the solar wind, the continual stream of electron 
and protons that shoot off the Sun.  But a strong magnetic field 
would have protected Mars' atmosphere, possibly letting Mars' 
surface be warm and wet enough for life to develop.


12] Valley J.W., Eiler J.M., Graham C.M., Gibson E.K.Jr., Romanek 
C.S., and Stolper E.M.  (1997) Low-temperature carbonate 
concretions in the martian meteorite ALH 84001:  Evidence from 
stable isotopes and mineralogy.  Science, 275, 1633-1638.

The temperature of formation of carbonate globules in ALH 84001 is 
important because the globules are hosts to the possible traces of 
ancient martian life (McKay et al., 1996).  The first estimates of 
the globules' formation temperature, <320C, relied on oxygen 
isotope measurements (Romanek et al., 1994); here, Valley et al. 
revisit the oxygen isotope measurements with a new improved 
analytical method and confirm the low formation temperature.

Valley et al.  used an ion microprobe to determine oxygen isotope 
abundances in the carbonate globules and other minerals in ALH 
84001.  The ion microprobe can produce analyses from very small 
spots, about 20 micrometers (m) in diameter, which is important 
because the carbonate globules are <200 m in diameter.  Valley et 
al. analyzed oxygen isotope ratios in carbonates from two separate 
ellipsoids, one of which was a composite of two smaller carbonate 
bodies.  To help calibrate the ion microprobe measurements, Valley 
et al. also obtained chemical analyses of these and nearby spots 
in ALH 84001 using an electron microprobe.

Valley's results are consistent with, and expand on, the earlier 
work of Romanek et al. (1994).  They found that the carbonate 
minerals were variably enriched in the heavy oxygen isotope 18O, 
with enrichments ranging from ?18O = 9.5 to 20.5 "per mil" (or 
parts per thousand).  Carbonate near the globule rims was much 
richer in 18O than carbonate from the cores, and the different 
globules had different 18O enrichments in their cores.

Valley et al. inferred that the carbonate globules formed at low 
temperatures because their chemical and isotopic variations could 
not have been preserved, if they had formed at high temperatures.  
Valley et al. estimate that the carbonate globules formed at 
<100C.  An absolute upper temperature limit from their results 
comes from assuming that the carbonates were in oxygen isotopic 
equilibrium with the surrounding pyroxene.  This upper limit on 
temperature is ~300C; the temperature had to have been lower 
because the pyroxene and carbonate were not in chemical 
equilibrium.

Valley et al.  also made some interesting discoveries and 
observations during their work:  (1) They also analyzed the 
carbonates for carbon isotope composition, and found some evidence 
for an organic carbon component that has relatively little of the 
heavy carbon isotope 13C.  This finding is one of a number of hints 
now of very "light," possibly organic, carbon in ALH 84001.  (2) 
Valley et al. found a veinlet of silica that cut across one of the 
carbonate globules.  This indicates that silicate minerals were 
mobile after the carbonate veinlets formed, and similar evidence 
was presented by other groups at the 28th Lunar and Planetary 
Science Conference.  (3) Valley et al. note that the near-absence 
of hydrous minerals in ALH 84001, long cited as a problem for a 
low-temperature origin of the carbonates, is not actually a 
problem at all.  There are many instances on Earth where low-
temperature carbonate veins cut silicate rocks without formation 
of hydrous silicate minerals.

The oxygen isotope abundance ratios measured by Valley et al.  
have been confirmed and extended by two other groups using similar 
ion microprobe techniques:  L. Leshin et al. (1997) and J. Saxton 
et al. (1997).  Although there are still some problems with 
calibrations and inter-laboratory biases, it seems indisputable 
that the carbonates in ALH 84001 contain relatively heavy oxygen 
(high ?18O) and that they are strongly zoned in oxygen isotope 
ratios from core to rim.

However, the meaning of this zoning is quite disputable.  Valley 
et al. have interpreted the zoning as most consistent with 
carbonate minerals growing, at low temperature, from a fluid that 
changed composition over time.  Their low temperature is 
consistent with, but not proof of, microbial life.  Leshin et al., 
on the other hand, interpret the oxygen isotope zoning as forming 
at higher temperatures in a closed system.  Higher temperatures 
here means 250C, too high for known Earth bacteria, but a far cry 
from the 500-700C suggested by some other investigators.


13] Jull A.J.T., Eastoe C.J., and Cloudt S.  (1997) Isotopic 
composition of carbonates in the SNC meteorites Allan Hills 84001 
and Zagami.  J. Geophys. Res. 102, 1663-1669.

The authors investigated the sources of the carbon in ALH 84001 
(and other martian meteorites), especially using radioactive 
carbon-14 (14C) as a marker for carbonates that formed on Earth.  
Radioactive 14C forms continuously in the Earth's atmosphere (and 
from nuclear bomb tests) and forms only sparingly in space, so the 
abundance of 14C in the carbonates is a clue to how much they have 
reacted with carbon from Earth.  The authors find that most of the 
carbonate in ALH 84001 contains 14C, so much 14C that it must have 
either formed on Earth or traded some of its martian carbon for 
Earth carbon.  The carbon in ALH 84001 with the least 14C is also 
the richest in the stable carbon isotope 13C, and its 13C abundance 
is the same as measured for martian carbonates in ALH 84001 and 
other martian meteorites.

This work and Jull et al. (1995) are important for understanding 
terrestrial contamination in ALH 84001.  The authors argue that a 
great proportion of the carbon and oxygen in the ALH 84001 
carbonates originated on Earth, and then diffused into the 
carbonate mineral grains in the meteorite.  This argument, if 
true, lends plausibility to the idea that the PAHs in ALH 84001 
are also terrestrial (Becker et al., 1997).  However, Wright et 
al.  (1997) suggest that the amount of 14C found here could also 
mean only limited contamination by Earth carbon.


14] Goswami J.N., Sinha N., Murty S.V.S., Mohapatra R.K., and 
Clement C.J.  (1997) Nuclear tracks and light noble gases in Allan 
Hills 84001:  Pre-atmospheric size, fall characteristics, cosmic 
ray exposure duration and formation age.  Meteor. Planet. Sci. 32, 
91-96.

As ALH 84001 traveled between Mars and the Earth, it was bombarded 
by cosmic rays, high-energy particles from the Sun and the galaxy.  
Interactions of cosmic-ray particles with meteorites leave 
characteristic signatures like the nuclear tracks produced by 
cosmic-ray heavy nuclei and trace abundances of the noble elements 
(e.g., neon and argon) resulting from nuclear interactions of 
cosmic ray protons with meteoritic matter.  Here the authors 
investigated the evidence for cosmic-ray bombardment in ALH 84001 
to understand what happened to this meteoroid after it left Mars 
and before it landed in Antarctica.  They found that ALH 84001 
formed approximately 4 billion years ago, and spent approximately 
17 million years exposed to cosmic rays; these numbers are 
consistent with results from many other groups.  In addition, the 
authors here deduce that ALH 84001 was approximately 20 
centimeters in diameter before it encountered the Earth, and that 
~85% of it burnt up as it passed through the Earth's atmosphere.  
They also suggest that ALH 84001 did not break up into multiple 
fragments as it fell through the Earth's atmosphere, and so it is 
also unlikely that additional fragments of this meteorite exist.

There may be calls for the Antarctic Search for Meteorites 
Program, ANSMET, to return to the Allan Hills area of Antarctica 
to search for more fragments of ALH 84001 rock.  The results in 
this paper suggest that returning to the Allan Hills for martian 
meteorites would be no more fruitful than collecting elsewhere in 
Antarctica.  In fact, ANSMET field parties have gathered 
meteorites from the Allan Hills area many times since their first 
visit in 1976.  In that time, only two martian meteorites have 
been found in the Allan Hills:  ALHA 77005 and ALH 84001.  These 
two meteorites are quite different, and could not be separate 
fragments from a single meteorite fall.


15] Becker L., Glavin D.P., and Bada J.L.  (1997) Polycyclic 
aromatic hydrocarbons (PAHs) in Antarctic Martian meteorites, 
carbonaceous chondrites, and polar ice.  Geochim. Cosmochim. Acta 
61, 475-481.

McKay et al. (1996) discovered that ALH 84001 contains polycyclic 
aromatic hydrocarbon molecules (PAHs) in moderate abundance, found 
that these PAHs were distinct from meteoritic and terrestrial 
PAHs, and found that the PAHs in ALH 84001 were intimately 
associated with the carbonate minerals that host other possible 
indications of fossil life.  Here, the authors evaluate whether 
the PAHs in ALH 84001 might be contaminants.

To see if the association of PAHs and carbonate minerals in ALH 
84001 really suggests that they formed together, the authors put 
carbonate mineral grains in water samples that contained PAHs--a 
standard--and a sample of Antarctic ice from the Allan Hills.  In 
both cases, the PAHs in the water attached themselves to the 
carbonate mineral grains.  From this result, the authors infer 
that the PAHs in ALH 84001 might have become associated with the 
carbonate minerals without any biologic action.

To see if the PAHs in ALH 84001 were actually different from those 
in other sources, the authors analyzed PAHs in the martian 
meteorite EETA 79001 (both carbonate minerals and bulk rock), in 
two carbonaceous chondrite meteorites, and in Antarctic ice from 
the Allan Hills.  The PAHs from these other samples are all 
similar to those in ALH 84001, especially in having strong signals 
from the few simplest PAHs (called parent or nonalkylated 
molecules).  The ALH 84001 PAHs are most similar to PAHs in 
carbonate minerals in the EETA 79001; both meteorites have similar 
simple PAHs and in similar small amounts of big complex PAHs.  The 
carbonates in EETA 79001 are known to be contaminated with carbon 
and organic molecules from Earth (Jull et al., 1995; McDonald and 
Bada, 1995), and so probably contaminated with Earth PAHs.  So, 
Becker et al.  conclude that the PAHs in ALH 84001 are probably a 
mixture of PAHs from Antarctic ice and PAHs from carbonaceous 
meteorites or interplanetary dust, which could have entered ALH 
84001 either on Earth or on Mars.  They see no clear evidence in 
the PAHs for a biological origin on Mars, and suggest that amino 
acids would be better biomarkers than PAHs.

This article is important for characterizing the PAHs from Earth 
that are likely to collect on meteorites as they sit in 
Antarctica, and would seem to weaken McKay et al.'s case for 
traces of martian fossils in ALH 84001.  But many questions are 
not yet answered.

1) The PAHs in ALH 84001 are not merely a mixture of PAHs from CM 
chondrites and from the Allan Hills ice.  The ice contains strong 
signals from the PAHs naphthalene (mass 128) and coronene (mass 
300), while carbonates in ALH 84001 contain neither (their Table 
1).  Other differences are apparent in the relative strengths of 
some PAH signals, and in the presence or absence of signals from 
some less-abundant PAHs.  Are these differences artificial, for 
instance because Becker et al. and McKay et al. used slightly 
different analytical techniques?  Or could the differences be real 
and significant for the origin of the PAHs?
2) The authors here showed that PAHs in water stick strongly to a 
calcium carbonate mineral, but is this relevant to ALH 84001?  
Calcium-rich carbonate minerals are rare in ALH 84001; most of its 
carbonate is rich in magnesium and iron.  Further, the calcium 
carbonate used in the experiments was not characterized, and may 
not have the same crystal structure as the carbonates in ALH 84001 
(calcite vs. aragonite vs. vaterite structure types); PAHs may 
bond differently to different carbonate mineral structures.
3) Becker et al. suggest that the PAHs in ALH 84001 are associated 
with the carbonate minerals because their experiment showed that 
PAHs in water stick strongly to a carbonate mineral.  But do PAHs 
prefer to stick to carbonates compared to the other minerals ALH 
84001?  The experiments of Becker et al. shed no light on this 
question.


16] Bradley J.  P., Harvey R.  P., and McSween H.  Y.  Jr.  (1996) 
Magnetite whiskers and platelets in ALH 84001 Martian meteorite:  
Evidence of vapor phase growth.  Geochim. Cosmochim. Acta 60, 
5149-5155.

McKay et al.  (1996) found that submicroscopic magnetite grains in 
the ALH 84001 carbonate globules are cuboid, teardrop, and 
irregular in shape" and have "no structural defects."  These 
magnetite crystals are similar to crystals produced by bacteria on 
Earth, and so McKay et al. suggested that the magnetites in ALH 
84001 could have been made by martian bacteria.

The authors here show that the submicroscopic magnetite grains 
also occur in other shapes and with structural defects.  Using 
transmission electron microscopy, the authors discovered whisker-
shaped magnetite crystals, five times as long as they are wide (10 
millionths of a millimeter by 50 millionths of a millimeter).  
Many of these magnetite whiskers contain a common kind of 
structural defect, a screw dislocation.  The authors also 
discovered blade- and plate-shaped crystals of magnetite, and many 
of them contain a structural defect called twinning.

On searching through other technical papers, the authors found 
that magnetite (and similar substances) grow in whisker shapes 
only from hot gases, hotter than 500C.  Hot gas like this occurs 
in nature near volcanoes, in structures called fumaroles, where 
the hot gases from a volcano or lava flow escape into the air.  In 
fact, whisker-shaped magnetite crystals were reported from a 
fumarole deposit in Indonesia by Symonds (1993).  Also, Bradley et 
al. could find no descriptions of bacterial magnetites that were 
blade shaped, plate shaped, whisker shaped, or that contained 
structural defects.

The authors conclude that the magnetites in the ALH 84001 
carbonate globules formed at high temperatures, and not from 
biological processes.  In addition, they note that the magnetite 
whiskers are approximately the same sizes and shapes as some of 
the possible fossilized bacteria shown in the McKay et al. (1996) 
paper.

This work can be viewed in two ways:  as a refutation of McKay et 
al.'s claims that the magnetites were made by microorganisms; or 
as an ambiguous result that merely shows that McKay et al.  were a 
bit exuberant in claiming that all the magnetite crystals were 
structurally perfect.

In the first view, it is clear that some of the magnetite crystals 
in the ALH 84001 carbonates do not have the shapes and structures 
of common biogenic magnetites.  This fact alone can be seen as a 
refutation of part of the McKay et al. hypothesis.  Because 
magnetite has a cubic crystal structure, it almost always grows as 
cubes, octahedra, or other compact shapes.  Elongated magnetite 
crystals are known to grow only from high-temperature gases, 
whether in nature or in the laboratory.  And this inference of 
high temperature, while not conclusive, is certainly inconsistent 
with life.

In the second view, most of the arguments in Bradley et al. (1996) 
are ambiguous.  While they all are interesting observations, none 
of them invalidates the hypothesis of McKay et al.

1) From the description in their paper, it is not clear that 
Bradley's magnetites are from the same layers and veins as the 
magnetites studied by McKay et al.
2) Although Bradley et al. did find structurally imperfect 
whisker-shaped magnetites, it would still appear that most of the 
magnetite crystals in the ALH 84001 carbonates are structurally 
perfect cuboids (and similar shapes).  So far, there is no proof 
that the whisker and cuboid magnetites formed at the same 
temperature.
3) To support a high-temperature origin for the ALH 84001 
magnetites, Bradley et al. refer to Symonds (1993), who found that 
whisker-shaped magnetite crystals grew from the hot gases given 
off by a volcano.  But Symonds suggested that temperature alone 
did not control whether the magnetite crystals grew as cubes or 
whiskers.  In fact, the highest-temperature magnetites grew as 
cubes, while the whisker-shaped crystals formed at lower 
temperatures where they grew very quickly (i.e., the gas was very 
supersaturated).  Whisker-shaped magnetites apparently have not 
been reported in low-temperature carbonate deposits, but it is 
quite possible that no one has looked carefully.

Bradley et al. (1997) will present these results and more at the 
Lunar and Planetary Science conference this week.  Thomas-Keprta 
et al. (1997) will counter with information that some bacteria do 
produce elongated magnetite crystals.


17] Shearer C.K., Layne G.D., Papike J.J., and Spilde M.N.  (1996) 
Sulfur isotope systematics in alteration assemblages in martian 
meteorite ALH 84001.  Geochim. Cosmochim. Acta 60, 2921-2926.

The element sulfur has two stable (not radioactive) isotopes, 32S 
and 34S.  The relative abundances of these sulfur isotopes, called 
the sulfur isotope ratio, can be affected by chemical processes, 
including metabolism by bacteria.  Many Earth bacteria can "eat" 
sulfur compounds and use them as fuel for growth.  Sulfur 
processed this way by bacteria is typically very depleted in 34S 
compared to the starting sulfur.  Nonbiological processes can 
enrich or deplete sulfur in 34S, but usually not so much as 
biological processes.

The authors here analyzed the isotopic composition of three pyrite 
grains associated with the carbonate globules of ALH 84001.  The 
pyrite grains all were enriched 34S compared to the solar system 
average; in the jargon, they had ?34S (pronounced "delta thirty-
four S") between +5 and +8 "per mil" (or parts per thousand).  
These enrichments in 34S suggest that the pyrite (and also the 
carbonate globules) formed at "low" temperatures, and that the 
sulfur in the pyrite was probably never processed by bacteria like 
those on Earth.

However, these results are ambiguous because the isotope ratio in 
Mars' starting sulfur is not known well.  If Mars' starting sulfur 
has ?34S near zero (the solar system average), the high ?34S of the 
pyrites could not come from biological processing, at least by 
bacteria like those on Earth.  Nor could the high ?34S develop 
during high-temperature chemical processes.  More likely, the 
pyrites grew from alkaline, oxygen-poor water at less than 150C.  
Lunar soils also have a high ?34S, which develops as meteorite 
impacts vaporize some of the soils.

On the other hand, if Mars' starting sulfur was rich in 34S (had a 
high value of ?34S), the isotopic composition of the sulfur could 
be consistent with either a high temperature or a biogenic origin.  
At high temperatures, inorganic processes do not separate the 
sulfur isotopes well, so a fluid rich in 34S would deposit pyrite 
rich in 34S.  Acidic waters at low temperature also would not 
separate sulfur isotopes well, so a fluid rich in 34S would deposit 
pyrite rich in 34S.  If Earth-type sulfur-eating bacteria were fed 
sulfur that was very rich in 34S, they would accumulate in them 
sulfur that was not so rich in 34S, perhaps similar to the sulfur 
in the pyrites.  Of course, if martian bacteria process sulfur 
differently from Earth bacteria, all bets are off.

It is easy to think that a low formation temperature for the 
carbonates in ALH 84001 means that they formed from martian life.  
But temperature and biology are separate issues.  Here, Shearer et 
al. infer that the pyrite and carbonates in ALH 84001 formed at 
low temperature without life!

Since this work was published, Greenwood et al. (1997) have also 
analyzed the isotopic composition of sulfur in ALH 84001, and in 
martian meteorites that have no known or suspected signs of life 
in them.  For ALH 84001, Greenwood et al.  got essentially the 
same sulfur isotope values as this paper; for the other martian 
meteorites, Greenwood et al.  got ?34S values between about +3 and 
-3.  These low numbers, so close to the average for the solar 
system, suggest that Mars' original sulfur was not very different 
from the solar system average, and so support Shearer's inference 
of a nonbiological origin for the pyrite.  The temperature of 
pyrite formation is not clear yet:  Shearer et al. suggest low 
temperature, while Greenwood et al. suggest high temperature.  
This work is continued in Shearer and Papike (1997) and Shearer 
(1997).


* After Science magazine published McKay et al.'s (1996a) article 
suggesting that they had recognized traces of ancient martian life 
in ALH 84001, many scientists wrote letters to Science disputing 
all or part of their results.  Science collected these comments 
and responses to them as "Evaluating the evidence for past life on 
Mars," Science, 274, pp.  2119-2125.  These summaries and 
commentaries are in the order that Science presented the 
originals.

18] Anders E. (1996) Science, 274, 2119-2121.

After praising the quality and depth of their observations, Anders 
comments that McKay et al. (1996a) did not consider nonbiological 
explanations for their discoveries:  "For all these observations, 
an inorganic explanation is at least equally plausible, and, by 
Occam's Razor, preferable." Anders then suggests nonbiological 
explanations for most of the chemical evidence for martian life in 
McKay et al.

Anders raises two objections to the description of PAHs in ALH 
84001 as implying biogenic activity.  First, PAH molecules form as 
readily from nonbiological chemical compounds as from biological 
compounds.  Given enough time and/or an elevated temperature, PAHs 
form readily from other organic materials; this process is 
documented in nature and utilized in industry.  Second, the 
spatial association of PAH molecules and the carbonate globules 
could have arisen without life.  Formation of PAHs can be 
accelerated (i.e., catalyzed) by the mineral magnetite, and 
submicroscopic grains of magnetite are abundant in the carbonate 
globules.

Anders also presented five objections to the arguments of McKay et 
al. concerning the minerals and chemical zoning of the carbonate 
globules.

1) The chemical zoning patterns in the carbonate globules could be 
a natural result of mineral solubilities, and need not imply the 
action of life.
2) The association of magnetite, iron sulfides (pyrrhotite), and 
carbonate minerals in ALH 84001 could form without the presence of 
life, as similar associations have formed in the carbonaceous 
chondrite meteorites.
3) The areas of partially dissolved carbonate minerals could form 
at normal temperatures and water compositions, without the action 
of life.
4) The greigite(?) iron sulfide mineral that McKay et al. found 
was not characterized well, and was not compared with nonbiogenic 
greigite.  Without this comparison, one cannot tell if the 
greigite(?) is actually relevant to the question of life.
5) Finally, the structure of the carbonate globules (claimed by 
McKay et al. to be evidence for a biological origin) was not 
compared to the structures of carbonate globules formed without 
assistance from life.  Without this kind of comparison, one cannot 
tell if the structures of the carbonate globules are relevant or 
not.

Before the matter of ancient martian life in ALH 84001 is 
completely resolved, all of Anders' points will need to be 
studied.  McKay et al. (1996b) and Clemett and Zare (1996) provide 
some answers in their responses to this comment.

The fundamental issue behind Anders' comment is scientific proof 
itself.  Can the martian-life-in-ALH-84001 hypothesis be examined 
piece by piece, one line of evidence at a time?  Or must all the 
evidence be considered together, as one complete package?

In natural sciences, it is rarely possible to prove that an idea 
is true--"proof" consists mostly of showing that an idea fits ("is 
consistent with") all the facts, and that all other ideas don't 
fit the facts or are too complicated.  Most often, though, 
scientists can think up many different ideas that can fit all the 
facts.  Then, they will commonly quote "Occam's Razor," which 
states that the simplest idea is more likely than the complicated 
ideas.  Unfortunately, what is simple to one scientist is 
needlessly complex to another.  McKay et al.'s paper and Anders' 
comment use different ideas of simplicity, and so arrive at 
different preferred conclusions.

McKay et al. invoked Occam's Razor (without naming it) in 
justifying a biological origin for all their observations:  
"Although there are alternative explanations for each of these 
phenomena taken individually, when they are considered 
collectively, particularly in view of their spatial association, 
we conclude that they are evidence for primitive life on early 
Mars." From this perspective, McKay et al.  did not need to 
consider nonbiological explanations for each observation, only 
nonbiological explanations of the all of the observations at once.  
They did not find any nonbiological explanations, and so had to 
accept the idea of martian life.

On the other hand, Anders invoked Occam's Razor (quoted above) to 
justify nonbiological processes for each individual observation.  
Anders did not search for a single nonbiological explanation for 
all the evidence, and did not consider how likely it was that all 
of his proposed processes could have affected small areas in a 
single rock.

To some extent, then, Anders and McKay et al. are not looking at 
the evidence in the same way; McKay et al. are "holists," and 
Anders is a "reductionist."  For the possible martian fossils, it 
remains to be seen which view of the world* is more useful.
* "Weltanschauung" to the philosophers.


19] Shearer C.K. and Papike J.J.  (1996) Science, 274, 2121.

Here, the authors summarize their sulfur isotope measurements that 
were reported earlier in Shearer et al. (1996), which are 
described below.  Shearer and Papike emphasize that the pyrite 
mineral grains that they analyzed earlier are related to the 
carbonate globules, and that the sulfur in the pyrite is enriched 
in the stable isotope 34S compared to the solar system average.  
Sulfur-eating bacteria on Earth produce mineral-like pyrite that 
is strongly depleted in 34S, so it is unlikely that the pyrite in 
ALH 84001 was made by Earth-type bacteria.  Martian bacteria could 
still be involved, however, if Mars itself was much richer in 34S 
than the Earth is, or if martian bacteria process sulfur 
differently from Earth bacteria.  For more detail, see the 
discussion of Shearer et al. (1996) below.

Gibson et al. (1996) respond directly to this comment.  McKay et 
al. (1996a) did not claim that the pyrite in ALH 84001 was 
biogenic, so, strictly speaking, this report by Shearer and Papike 
is not relevant to the current hypothesis of ancient martian 
fossils in ALH 84001.  However, the pyrite crystals are spatially 
associated with the carbonate globules, and it would have seemed 
reasonable that the pyrite and the carbonates grew from the same 
fluids with the same sulfur isotope abundances.  On the other 
hand, if the pyrite had a deficiency of 34S (such as might be 
expected from biogenic pyrite on Earth), it might possibly have 
been cited by Gibson et al.  (1996) as further evidence of 
biogenic activity in ALH 84001.

This work has continued in Shearer (1997) and Shearer and Papike 
(1997).


20] Bell J.F.  (1996) Science, 274, 2121-2122.

Bell's comment centers on the PAH organic molecules found in ALH 
84001 by McKay et al. (1996); Bell accepts that these PAHs are 
martian, but not that they imply martian life.  He suggests that 
the PAHs may have come from meteorites falling onto Mars, just as 
a few percent of the Moon's soil is made of meteorite debris.  
Specifically, Bell suggests that the PAHs in ALH 84001 came from 
material like the C2 carbonaceous chondrite meteorites, and 
suggests that the sources of this C2 material included the moons 
of Mars, Phobos and Deimos.

McKay et al. (1996a) and Becker et al. (1997) agree with Bell that 
the PAHs in ALH 84001 are similar to those in the C2 carbonaceous 
chondrites.  The PAHs in these meteorites are not identical, but 
are they similar enough to suggest a common origin?  Bell and 
Becker say "yes," McKay et al.  say "no, especially in light of 
the associated evidence."  Bell is correct that a few percent of 
the lunar soil is made of meteoritic material like C2 carbonaceous 
chondrites (a point I mistakenly disputed in earlier versions of 
this commentary).  Although few meteorites are carbonaceous, the 
vast majority of interplanetary dust is like C2 carbonaceous 
chondrites, and that dust makes up most of the mass that falls 
onto planets.  The moons of Mars are very dark; their darkness 
might be from the carbon in carbonaceous chondrite material, but 
their darkness might have other causes (Murchie et al., 1991).


21] Clemett S.J. and Zare R.N.  (1996) Science, 274, p.  2122-
2123.

Clemett and Zare are among the authors in the original McKay et 
al.  paper, and they respond to comments of Anders and Bell 
related to PAHs, the organic molecules called polycyclic aromatic 
hydrocarbons.  Clemett and Zare emphasize that the PAHs they found 
in ALH 84001 are not laboratory contaminants, and are apparently 
only a small part of all the organic materials in ALH 84001.  They 
agree with Anders (1996) that some of the PAHs in ALH 84001, the 
low-mass ones, could have formed by inorganic processes at high 
temperature.  The high-mass PAHs, although less abundant, are very 
similar to the break-down products of kerogen, a variety of solid 
organic material that is common on Earth and in the carbonaceous 
chondrite meteorites.  Earth kerogen formed from living matter, 
and meteorite kerogen did not.  Clemett and Zare leave with two 
questions:  how could nonbiologic kerogen get into an igneous 
rock, one that solidified from molten lava; and how could 
nonbiologic kerogens (or PAHs) come to be associated only with the 
carbonate globules in ALH 84001?

As an aside, Clemett and Zare also reply to comments from Simoneit 
and Hites and from Requejo and Sassen, but neither of these 
comments was printed in Science.

Clemett and Zare agree that some nonbiological processes could 
have produced the distribution and abundances of PAHs that they 
observed in ALH 84001:  the low-mass PAHs could be the product of 
inorganic reaction at high temperature, and the high-mass PAHs 
could form by the low-temperature reaction of inorganic kerogen.  
But the issue is whether the PAHs in ALH 84001, in their 
association with the carbonate globules, are more easily explained 
by biological or nonbiological mechanisMs. A nonbiological 
scenario would have to start with carbon-rich gas reacting at high 
temperature to form the low-mass PAHs.  Then, nonbiologic kerogen, 
from some other source, would have to decompose at low temperature 
into high-mass PAHs.  Either the kerogen or the high-mass PAHs 
would have to infiltrate ALH 84001, adhere only to the carbonates, 
and not displace the low-mass PAHs already in place.  Is this 
sequence of events actually simpler and more believable than the 
growth, death, and decomposition of martian bacteria?


McKay D.S., Thomas-Keprta K.L., Romanek C.S., Gibson E.K.Jr., and 
Vali H.  (1996b) Science, 274, 2123-2125.

Here, McKay et al.  respond directly to Anders' (1996) comments 
about minerals in the carbonate globules and about the morphology 
of possible fossil shapes in ALH 84001; Clemett and Zare responded 
to Anders' comments on PAHs.  Anders' comments stressed the 
similarity of the carbonate globules and their minerals to some 
grains in the C1 carbonaceous chondrite meteorites.  McKay et al.  
agree that similarities are present, but emphasize the significant 
differences between ALH 84001 and the C1 carbonaceous chondrites.  
In particular, ALH 84001 is an igneous rock, while the C1s have 
been altered at low temperatures to clays, serpentine, and similar 
water-bearing silicate minerals.  McKay's responses to Anders' 
comments are keyed to Anders' points (as above).

1) McKay et al. agree with Anders that the chemical zoning pattern 
in the carbonate globules could have been produced by inorganic 
crystallization.  They stress, however, that the repetitive 
(oscillatory) zoning pattern and composition difference between 
one globule and another can only arise from complex inorganic 
processes.
2) Anders compared the carbonate-magnetite-sulfide minerals in ALH 
84001 to those in C1 carbonaceous chondrite meteorites.  McKay et 
al. respond that, in effect, the C1s are not good analogies.  
Magnetite grains in carbonate minerals are much larger in C1s than 
in ALH 84001.  And magnetite grains in carbonate minerals in C1s 
do not have cuboid shapes as they do in ALH 84001.
3) McKay et al. agree with Anders that the partially dissolved 
carbonate grains in the carbonate globules could have formed in 
nearly neutral (nonacidic or alkaline) water, and do not require 
the moderate acidity invoked in McKay et al. (1996a).  McKay et 
al. restate that the globular morphology of the ALH 84001 
carbonates is similar to those formed by bacteria on Earth, and 
unlike the carbonate areas formed inorganically in the C1 
carbonaceous chondrites.  They stress, however, that no matter 
what the exact water composition, no simple inorganic process can 
form all the observed structures and minerals in the carbonate 
ellipsoids.
4) On the matter of greigite(?) in ALH 84001, Anders had hoped to 
see it compared to nonbiogenic greigite.  McKay et al. respond 
that life seemed to be involved with the formation of all greigite 
on Earth, at least all the greigite that they were aware of.  
Living organisms either produce greigite directly themselves, or 
produce the hydrogen sulfide gas that goes to form greigite.
5) Anders commented that the structures of the carbonate globules 
should have been compared directly to carbonates that grew without 
assistance from life.  McKay et al. respond that the shape of 
possible fossil forms is not yet definitive proof that they are 
real fossils, that similar shapes have not been found in lunar or 
asteroidal meteorite samples, and that more work is needed.  They 
also agree with Anders that a proof that the fossil shapes 
actually are fossils would make all the other arguments 
irrelevant.

I see two underlying themes in this response:  that ALH 84001 is 
unique, and that the minerals and structures of the carbonate 
globules are too complex for any simple inorganic processes.  
There is, of course, no doubt that ALH 84001 is unique.  But 
Anders and McKay et al.  disagree on whether the carbonate 
globules in ALH 84001 are so unusual that seemingly similar 
structures in the C1 carbonaceous chondrites are not relevant.  It 
has been suggested that the C1 carbonaceous chondrites are from 
Mars (Brandenburg, 1996), but most evidence seems to suggest 
otherwise (Treiman, 1996).

McKay et al. emphasize the complexity of the carbonate globules, 
both in the chemical zoning of their carbonate minerals and in the 
groupings of minor minerals in the carbonates.  The complexity 
alone suggests to them the action of complex biological systems, 
and they want to consider all the evidence in McKay et al.  
(1996a) as a systematic whole, and not as a set of separate 
pieces.  Quoting from their response, the formation of the 
carbonate globules "cannot be simple equilibrium, and must 
include changing conditions and kinetic effects.  Whether such 
models are more plausible than biogenic models is a matter of 
judgment."

As an aside, the fifth point of Anders' comments seems to refer to 
the shapes and structures of the carbonate globules, while McKay 
et al. here responded about the sausage-shaped things that might 
be fossil bacteria.  Some critical sentence or idea may have been 
lost.


22] Gibson E.K.Jr., McKay D.S., Thomas-Keprta K.L., and Romanek 
C.S.  (1996) Science, 274, 2125.

The authors respond directly to Shearer and Papike's (1996) claim 
that sulfur isotope ratios on pyrites near the carbonate globules 
probably mean that they formed without help from bacteria.  The 
authors note that the pyrite grains may not be relevant to McKay 
et al.'s hypothesis because pyrite is not in the carbonate 
globules, it did not grow with the structurally flawless 
submicroscopic magnetites, and is not associated with the PAHs.  
The submicroscopic sulfur-bearing minerals, pyrrhotite and 
greigite, which are part of McKay et al.'s hypothesis, will be 
very difficult to analyze for sulfur isotope ratios.  These 
sulfur-bearing grains are so small that the carbonate and 
magnetite grains around them would also end up being analyzed for 
sulfur.  The carbonate and magnetite grains don't contain sulfur, 
but they do contain lots of oxygen, and oxygen molecules can 
masquerade as sulfur atoms in these isotope analyses.  Sulfur 
atoms with mass 32, 32S, can be mimicked by the oxygen molecule 
16O16O; and sulfur atoms with mass 34, 34S, can be mimicked by the 
oxygen molecule 16O18O.

Greenwood et al. (1997) report that the isotope ratio for sulfur 
from the carbonate globules, presumably from pyrrhotite, is nearly 
the same as for the pyrite grains.  Their sulfur isotope of the 
pyrrhotite analyses are quite imprecise (?34S somewhere between +12 
and -1), and it is not clear if they considered the possible 
interferences from molecular oxygen.


References

Bogard D.D.  and Garrison D.H.  (1997) 39Ar-40Ar age of ALH 84001.  
In Clifford S. and Treiman A.H. eds., Conference on Early Mars:  
Geologic and Hydrologic Evolution, Physical and Chemical 
Environments, and the Implications for Life.  L.P.I.  Contribution 
916, 10-12.

Bradley J.P., Harvey R.P., and McSween H.Y.Jr.  (1997) Magnetite 
whiskers and platelets in the ALH84001 martian meteorite:  
Evidence of vapor phase growth.  Lunar Planet. Sci. XXVIII.

Brandenburg J.E.  (1996) Mars as the parent body of the C1 
carbonaceous chondrites.  Geophys. Res. Lett., 23, 961-964.

Greenwood J.P., Riciputi L.R., and McSween H.Y.Jr.  (1997) Sulfur 
isotopic variations in sulfides from shergottites and ALH 84001 
determined by ion microprobe:  No evidence for life on Mars.  
Lunar Planet. Sci. XXVIII.

Jakosky B.M.  and Jones J.H.  (1997) The history of Martian 
volatiles.  Rev. Geophys., 35, 1-16

Jull A.J.T., Eastoe C.J., Xue S., and Herzog G.F.  (1995) Isotopic 
composition of carbonates in the SNC meteorites Allan Hills 84001 
and Nakhla.  Meteoritics, 30, 311-318.

Kjarsgaard B.A.  and Hamilton D.L.  (1989) The genesis of 
carbonatites by immiscibility.  388-404 in Bell ed. Carbonatites:  
Genesis and Evolution, Unwin-Hyman, Boston.

Leshin L., McKeegan K.D., and Harvey R.P.  (1997) Oxygen isotopic 
constraints on the genesis of carbonates from martian meteorite 
ALH 84001.  Lunar Planet. Sci. XXVIIII, 805-806.

McDonald G.D. and Bada J.L.  (1995) A search for endogenous amino 
acids in the Martian meteorite EETA79001.  Geochim. Cosmochim. 
Acta, 59, 1179-1184.

McKay D.S., Gibson E.K.Jr., Thomas-Keprta K.L., Vali H., Romanek 
C.S., Clemett S.J., Chilier X.D.F., Maechling C.R., and Zare R.N.  
(1996a) Search for past life on Mars:  Possible relic biogenic 
activity in martian meteorite ALH 84001.  Science, 273, 924-930.

Murchie S., Britt D., Head J., Pratt S., Fisher P., Zhukov B., 
Kuzmin A., Ksanfomality L., Zharkov A., Nikitin G., Fanale F., 
Blaney D., Robinson M., and Bell J.  (1991) Color heterogeneity of 
the surface of Phobos:  Relationships of geologic features and 
comparison to meteorite analogs.  J. Geophys. Res., 96, 5925-2945.

Saxton J.M., Lyon I.C., and Turner G.  (1997) Oxygen isotope ratio 
zoning in ALH 84001 carbonates (abstract).  In Conference on Early 
Mars:  Geologic and Hydrologic Evolution, Physical and Chemical 
Environments, and the Implications for Life (S. Clifford et al., 
eds.), pp. 70-72.  LPI Contribution No. 916.  
[http://cass.jsc.nasa.gov/lpi/meetings/earlymars/pdf/program.pdf]

Shearer C.  K.  (1997) Sulfur isotopic systematics in ALH 84001.  
Open-and closed-system behavior of sulfur in a martian 
hydrothermal system.  Lunar Planet. Sci. XXVIII.

Shearer C.  and Papike J.  (1997) The petrogenetic relationship 
between carbonates and pyrite in martian meteorite ALH 84001.  
Lunar Planet. Sci. XXVIII.

Symonds R.  (1993) Scanning electron microscope observations of 
sublimates from Merapi Volcano, Indonesia.  Geochem. J., 26, 337-
350.

Thomas-Keprta K.L., Romanek C.S., Wentworth S.J., McKay D.S., 
Fisler D., Golden D.C., and Gibson E.K.  (1997) TEM analysis of 
fine-grained minerals in the carbonate globules of martian 
meteorite ALH 84001.  Lunar. Planet Sci. XXVIII.

Treiman A.H.  (1996) Comment on "Mars as the parent body of the CI 
carbonaceous chondrites" by J.E. Brandenburg.  Geophys. Res. 
Lett., 23, 3275-3476.

Valley J.W., Eiler J.M., Graham C.M., Gibson E.K.Jr., Romanek 
C.S., and Stolper E.M.  (1997) Low-temperature carbonate 
concretions in the martian meteorites ALH 84001:  Evidence from 
stable isotopes and mineralogy.  Science 275, 1633-1638.

Wadhwa M. and Lugmair G.W.  (1996) The formation age of carbonates 
in ALH 84001 (abstract).  Meteoritics 31.  A145.

Wright I.P., Grady M.M., and Pillinger C.T.  (1997) Evidence 
relevant to the life on Mars debate.  (1) 14C results.  Lunar 
Planet. Sci. XXVIII.
------------------------------------------------------------------

MARS SOCIETY FOUNDING CONVENTION
Mars Society release

31 March, 1998

August 13-16, 1998
University of Colorado, Boulder

This summer, over 1000 scientists, engineers, visionaries, 
philosophers, explorers, businessmen, journalists, historians, 
politicians, and other citizens will join in a historic gathering 
to found an association committed to the exploration and 
settlement of Mars by both public and private means.  Be there.

Sessions Announced!
Thirty Six sessions are now planned for the conference.  These 
sessions
include:
1.	Concepts for Privately Funded Mars Missions
2.	Current Plans for Robotic Mars Exploration
3.	Mars Meteorite AH84001:  Evidence for Life?
4.	Latest Findings of the Pathfinder and Mars Global Surveyor 
Missions
5.	The Search for Life on Mars
6.	The Contamination Hazard:  Fact or Fiction
7.	Concepts for Future Robotic Mars Exploration Missions
8.	Piloted Mars Exploration Missions
9.	Use of Local Resources
10.	Methods of Construction on Mars
11.	Advanced Propulsion
12.	Options for Producing Power On Mars
13.	Gaining Access to the Martian Hydrosphere
14.	Biomedical Issues in Mars Exploration
15.	Space Launch Options for Mars Exploration and Settlement
16.	Life Support Technology
17.	Human Factors
18.	Technologies for Achieving Long Range Mobility on Mars
19.	Concepts and Technologies for a Permanent Mars Base
20.	The Economics of Mars Colonization
21.	Social Aspects of Mars Colonization
22.	Timekeeping and Calendar Systems for Mars
23.	Mars as a Way Station to Worlds Beyond
24.	Terraforming Mars
25.	Mars Exploration and American Public Policy
26.	International Collaboration as a Path to Mars
27.	The Need for Law on Mars
28.	Risk and Exploration:  How Much is Acceptable?
29.	Methods of Public Outreach
30.	Mars and Education
31.	Mars and the Arts
32.	The Role of Women in Exploration and Settlement
33.	Potential Philosophical Impacts of Mars Exploration
34.	The Human Need to Explore
35.	The Significance of the Martian Frontier for Future Human 
History
36.	The Founding Declaration of the Mars Society

Conference Registration Fee:  $140 before June 30, 1998, $180 
afterwards.

Call for Papers
Papers for presentation at the convention are requested dealing 
with all matters (science, engineering, economics, and public 
policy) associated with the exploration and settlement of Mars.  
Abstracts of no more than 300 words should be sent by 5/31/98 to:  
Mars Society, Box 273, Indian Hills, CO 80454 USA

Written papers are not required for presentation at the 
conference.  However papers submitted in writing will be published 
in a series of special issues in the Journal of the British 
Interplanetary Society and compiled for publication in book form 
to be published by Univelt Inc.

Co-sponsors Boost Effort
The following organizations have stepped forward to co-sponsor the 
Founding Convention of the Mars Society:
The National Space Society
The British Interplanetary Society
The World Space Bar
United Societies in Space
Pioneer Astronautics
The Boulder Center for Science and Policy
Fisher Space Pen

Journal Founded!
The Mars Society has initiated an electronic magazine entitled, 
New Mars:  The Journal of the Martian Frontier.  New Mars will 
feature news of technical advances, scientific findings, political 
developments, as well as feature articles discussing scientific, 
engineering, social, historic, and public policy issues relating 
to the exploration and settlement of Mars.  The editor of New Mars 
will be Richard Wagner, the former editor of the National Space 
Society's Ad Astra Magazine.  Contributions are solicited.

Further information on both the Founding Convention and the New 
Mars journal can be found at:  http://www.nw.net/mars
------------------------------------------------------------------

GALILEO EUROPA MISSION STATUS
JPL release

25 March, 1998

NASA's Galileo spacecraft is sending to Earth the final pictures 
and science information stored on its onboard tape recorder during 
the December 1997 flyby of Jupiter's moon Europa.  These data 
include an observation of a region on Europa with wedge-like 
features, which may indicate that a liquid ocean lies under the 
surface, and another observation of volcanic activity on Jupiter's 
moon Io.  An observation by the photopolarimeter radiometer is 
part of a series designed to look for hot spots which might offer 
evidence that a heat source on Europa led to the creation of a 
liquid ocean or slush.

The flight team is preparing for Galileo's next Europa flyby, 
scheduled for Sunday, March 29, at an altitude of about 1,645 
kilometers (1,022 miles).  A flight path correction was performed 
on Friday, March 13, and an attitude update was performed 
Thursday, March 19.  Both events went well, even though they used 
the gyroscopes, the known cause of recent anomalous behavior of 
the attitude control system.  Precautions were taken to prevent 
the gyroscope anomaly from affecting activities.  The flight team 
has decided the upcoming Europa flyby will be performed without 
the gyros.  This means there will be no way to compensate for any 
wobble that may be present in the spacecraft's spin axis, and 
instrument pointing and stability are likely to be degraded 
somewhat.  Only very minimal effects on images taken by the 
spacecraft's camera are expected, with a somewhat greater impact 
anticipated for another instrument, the near infrared mapping 
spectrometer.

On Thursday, March 26, Galileo will perform its final flight path 
correction before Sunday's Europa flyby, and the flight team will 
send computer commands to control all spacecraft activity during 
the encounter period.  Regular maintenance of Galileo's onboard 
tape recorder will be performed Friday.

Galileo's flight team is nearing completion of modifications to 
the attitude control system flight software that would allow the 
spacecraft to operate with only one gyro.  Although this won't be 
a complete "fix," it will eliminate the need for workarounds 
currently being used for maneuvers and attitude updates.

The recent anomalies may be caused by Galileo's long-term exposure 
to Jupiter's intense radiation.  The spacecraft successfully 
completed its primary mission in December 1997 and is now in its 
two-year extension, the Galileo Europa Mission.  The flight team 
will continue to monitor the radiation's impact, but current plans 
include five more Europa flybys, four Callisto encounters, and one 
or two of Io, depending on spacecraft health.
------------------------------------------------------------------

GALILEO SOLID STATE IMAGING FULL DATA RELEASED
JPL release

26 March 1998

All images obtained by the Galileo Solid State Imaging (SSI) 
system during the spacecraft's first four orbits (G1, G2, C3 and 
E4) of Jupiter are now validated and available.  Images and data 
obtained by NASA/JPL's Galileo mission have been available on an 
ongoing basis during the spacecraft's journey through the Jovian 
system in order to share with the public the excitement of 
exploration and new discoveries being made via the NASA/JPL 
Galileo spacecraft.  Galileo scientists have a one year period set 
aside for the process of calibrating and validating the data.  The 
full digital images necessary for scientific analysis are released 
within one year of receipt of an orbit's last data.

Some of the BEST of the IMAGE PRODUCTS from the ongoing public 
releases are available now in multiple formats on the Planetary 
PhotoJournal web pages.
*G1 IMAGE PRODUCTS
*G2 IMAGE PRODUCTS
*C3 IMAGE PRODUCTS
*E4 IMAGE PRODUCTS

http://www.jpl.nasa.gov/galileo/sepo/fulldata.html

*ALL IMAGES from the first four orbits (G1, G2, C3 and E4) are 
merged and validated and available via the Planetary Data System.
*Primary Mission (6/96 - 12/97) Release Schedule for validated 
data sets * ALL Galileo Cruise Phase (10/89 - 12/95) Data

ALL IMAGING DATA from G1, G2, C3 and E4 is available via the 
Planetary Data System (PDS) Imaging Node at http://www-
pdsimage.jpl.nasa.gov/PDS/

The PDS offers a simple query interface to access all available 
G1, G2, C3 and E4 data.  It allows the user to search by various 
parameters such as target name, spacecraft clock, 
latitude/longitude, filter, phase angle, exposure, gain, and 
compression ratio.  PDS will continue to expand and improve this 
interface to include queries for any label parameters and, by the 
end of 1997, a format to select data via a map interface.

To accommodate the various needs of the scientific community, the 
archived files are raw data files which merge the multiple 
downlinks of data to provide the best final version of an image.  
Supporting data such as calibration files are available now and 
will be available through PDS within a few weeks.  Such files 
include dark currents, radiometric calibrations, blemishes, hot 
pixels, etc..

Galileo Primary Mission (6/96-12/97) Solid State Imaging Orbital 
Data Sets Public Release Schedule

Orbit 1 (G1)	September 06, 1997
Orbit 2 (G2)	November 04, 1997
Orbit 3 (C3)	December 19, 1997
Orbit 4 (E4)	February 20, 1998
Orbit 6 (E6)	April 05, 1998
Orbit 7 (G7)	May 07, 1998
Orbit 8 (G8)	June 25, 1998
Orbit 9 (C9)	September 17, 1998
Orbit 10 (C10)	November 06, 1998
Orbit 11 (E11) & GEM Schedules will be posted when available.
--------------------------------------------------------------------------------

TODAY ON GALILEO
JPL releases

28 March, 1998

The second science encounter of the Galileo Europa Mission, the 
follow on to Galileo's primary mission, started today when 
encounter-related computer commands began executing at 5 am, 
Pacific Time.  For the next three days, science instruments 
onboard the Galileo spacecraft will gather more information on the 
Jupiter system and its intriguing moons.  The information will be 
stored on the onboard tape recorder for later playback.  Once 
again, the bulk of the science observations will focus on 
Jupiter's moon Europa, but Jupiter, Jupiter's magnetic and 
electric field environment, and each of the other three Galilean 
moons:  Io, Ganymede and Callisto, are also observed.

This encounter is being performed without the gyroscopes.  That's 
because of the recent discovery of further degradation of the 
anomalous behavior of the spacecraft's attitude control subsystem.  
During data collection by the remote sensing instruments (camera, 
spectrometers and radiometer), the gyroscopes are used to improve 
the stability of instrument pointing.  They detect small wobbling 
of the spacecraft and compensate to keep the instruments steady.  
Without the gyros, no motion compensation is available.  This is 
expected to result in a small degradation in the quality of the 
data that is gathered.

As the spacecraft flies through the Jupiter system, it passes 
points of closest approach to each of the bodies of the system.  
Today, the spacecraft passes within 250,000 kilometers (155,000 
miles) of Io and 632,000 kilometers (393,000 miles) of Jupiter at 
8:48 pm and 11:59 pm, respectively, both in Pacific Time.

The fields and particles instruments kick off the science data 
gathering activities by initiating a low-rate survey (information 
is collected at a rate of only a few bits per second) of Jupiter's 
magnetic and electric field environment, also known as the 
magnetosphere.  Because of the low rate, this data can be packaged 
and transmitted to Earth almost immediately.  This type of 
observation is said to be performed in 'real-time'.  The survey is 
performed continuously for the duration of the encounter and the 
information obtained will provide scientists with a context for 
data gathered at a higher time resolution (hundreds of bits per 
second) later in the encounter.  The information will also add to 
the existing record of orbit-to-orbit of activity levels within 
the inner, most active, portions of the magnetosphere.

The first remote sensing observation of the encounter is performed 
by the Ultraviolet Spectrometer (UVS).  This observation of Europa 
will provide data on Europa's atmosphere.  Also obtained on 
previous orbits, this information allows scientists to monitor 
changes in the characteristics of the atmosphere from orbit to 
orbit.  Large changes in these characteristics could be indicative 
of geologic activity on the surface of Europa.  A small 
observation of Jupiter is performed next by the Near Infrared 
Mapping Spectrometer (NIMS).  The information gathered by this 
observation is designed to study long term changes in the 
composition and temperature of Jupiter's atmosphere.

As the spacecraft approaches its point of closest approach to Io 
for this orbit, the science instruments turn their attention to 
this fiery moon.  The UVS instrument performs an atmospheric 
monitoring observation similar to the one performed earlier on 
Europa.  This is followed by a series of color pictures taken by 
the camera of Io's north and south pole regions.  These pictures 
will improve the detail of these regions by providing resolutions 
of 3 kilometers (1.8 miles) per picture element.  The best color 
resolution obtained during Galileo's primary mission was 10 
kilometers (6.2 miles) per picture element.  Monochrome images as 
good as 2.5 kilometers (1.5 miles) per picture element were 
obtained in the primary mission, but the color in these new images 
will be critical to identifying surface materials.  The pictures 
will also be useful to scientists as they plan observations for 
the return to Io at the end of the Galileo Europa Mission.

The photopolarimeter radiometer (PPR) contributes further to the 
Io data set for this orbit with an observation designed to 
characterize the different temperatures on Io's surface.  This is 
followed by a joint observation of Io's surface performed by the 
NIMS instrument and the UVS instrument.  The observation is 
designed to keep track of any changes due to volcanic activity.


29 March, 1998

The spacecraft continues to make its way through the Jupiter 
system for the 14th time since June 1996.  Science information has 
been collected on 11 of the previous 13 orbits, 11 of which 
occurred during the Galileo primary mission.  Today's observation 
schedule is heavily focused on Jupiter's moon Europa as the 
spacecraft flies within 1,645 kilometers (1022 miles) of its 
surface at 5:21 am, Pacific Time.  Later in the day, at 4:09 pm, 
the spacecraft will pass the point of closest approach to Ganymede 
at a distance from the surface of 918,000 kilometers (571,000 
miles).

Many different areas of scientific interest on Europa are covered 
by today's observing activities.  The radio science team, for 20 
hours surrounding the point of closest approach, measures changes 
in Galileo's radio frequency due to Europa's gravitational pull on 
the spacecraft.  By using the Doppler effect, the radio science 
team will be able to use these measurements to refine the map of 
the gravity field produced by Europa.  Also tied to closest 
approach, the fields and particles instruments will perform a high 
time-resolution observation, for just under an hour, of Jupiter's 
magnetic and electric field environment in the region of space 
near Europa.  This will add to the scientific knowledge of the 
interaction between Europa and the magnetosphere.

The photopolarimeter radiometer performs three observations of 
Europa today.  Together they are designed to determine the 
temperature variation across Europa's surface and how it relates 
to different surface ages, how the surface might have been put 
together, or the different materials on the surface.  Two of these 
observations are performed at better resolutions than was possible 
during Galileo's primary mission.  The resolution of the third is 
comparable.  Three other global scale observations are performed 
during the day -- one by the spacecraft's camera, or solid-state 
imaging (SSI) subsystem, and two by the Near Infrared Mapping 
Spectrometer (NIMS).

Among the specific regions of Europa that Galileo looks at today, 
we start with a region characterized by rifts or crevasses in 
Europa's surface observed by NIMS together with the Ultraviolet 
Spectrometer (UVS).  This is followed by a couple of observations 
of the Mannann'an crater region performed by the SSI instrument.  
The pair of images is designed to provide stereo coverage of this 
region.  A region of dark spots is also observed twice by the 
camera.  These two images will also result in stereo coverage of 
this region, which also lies within regional data obtained during 
its orbit in November 1997.  In addition, a transition from a dark 
spot region to a region of pull-apart wedge shapes is observed by 
NIMS and is accompanied by the UVS instrument.

Later in the day, a region of triple-bands is observed by all 
three instruments (SSI, NIMS, UVS).  Remember that triple-bands 
are believed to be formed when Europa's surface cracks, material 
upwells from below the surface and spills to both sides of the 
central crack.  Coverage of this region is planned to be obtained 
during the the Europa orbit in February 1999.  A transition region 
between bright plains, pull-apart wedges and dark material is also 
observed by all three instruments.

A high-resolution picture of the Tyre Macula region is obtained by 
the SSI instrument.  This region was observed at a lower 
resolution in the primary mission's Ganymede orbit in April 1997, 
and an observation is planned at even higher resolution during the 
Europa encounter this coming May.  The SSI instrument also 
performs a photometry observation of the surface of Europa.  These 
photometric measurements will tell us how intensely light is 
reflected from the surface and provide more information on its 
makeup.

Two non-Europa observations are performed today.  The first is a 
global color image of Ganymede performed by the SSI instrument.  
This image will provide data on the radius, shape, color, and 
photometry of Ganymede as well as the mobility of frost on its 
surface.  Also observed by SSI is Io while eclipsed from the sun 
by Jupiter.  These eclipse images are considered one of the best 
ways to discover new lava flows, monitor lava temperatures, and 
study the interaction between volcanic plumes, Io's atmosphere and 
Jupiter's magnetosphere.

For more information on the Galileo spacecraft and its mission to 
Jupiter, please visit the Galileo home page:
http://www.jpl.nasa.gov/galileo/
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End Marsbugs Vol.  5, No.  9














