Jupiter
Jupiter
Jupiter, fifth planet from the sun and the largest planet in the earth's solar system. With the exception of the sun, the moon, and Venus, Jupiter is the brightest object in Earth's sky-more than three times brighter than Sirius, the brightest star. Due to its prominence in the sky, the ancient Romans named Jupiter for Jove, the chief god of Roman mythology.
Jupiter orbits the sun at an average distance of 780 million km (484 million mi), which is about five times the distance from Earth to the sun. Jupiter's year, or the time it takes to complete an orbit about the sun, is 11.9 Earth years, and its day, or the time it takes to rotate on its axis, is about 9.9 hours, less than half an Earth day.
Unlike the rocky inner planets of the solar system (Mercury, Venus, Earth, and Mars), Jupiter is a dense ball of gas. It has a relatively small core of molten rock and iron, but Jupiter has no solid surfaces. Jupiter's mass is about 318 times the mass of Earth and its diameter is about 11.2 times the diameter of Earth. The force of gravity at the level of the highest clouds in Jupiter's atmosphere is about 2.5 times the force of gravity on Earth.
Because Jupiter has such a large diameter and high rate of rotation, material at the surface must travel quickly to circle the planet. This speed gives the material a great deal of momentum, or a strong tendency to fly away from the planet and continue traveling in a straight line through space. Material at the equator has the highest speed because, in a Jovian day, it must travel the greatest distance to circle the planet. Therefore, material at the equator has the greatest momentum, and the strongest tendency to fly away from the planet. Because of Jupiter's weak, gaseous structure, the planet can not hold this material in as well as a more solid planet could, which results in Jupiter having the distorted shape of a flattened ball. The diameter of its equator is 143,000 km (89,000 mi), yet the diameter through its axis of rotation is only 133,700 km (83,000 mi).
