by Steven Mars

Created on: November 07, 2008   Last Updated: November 02, 2011

Jupiter is the largest planet in the solar system. It was named after the Roman chief god Jupiter. Its diameter of 88,846 miles is 13,948 miles larger than Saturn's 74,898 mile diameter. Jupiter’s diameter is larger than Earth’s diameter of 7,926 miles by 80,920 miles. Jupiter is the fifth planet from the sun. Mercury, Venus, Earth, and Mars are closer to the sun in that order. Farther away are Saturn, Uranus, Neptune, and Pluto also in that order. Its distance from the sun is 483,682,810 miles compared to 92,955,820  miles for Earth. This makes Jupiter 390,726,990 miles farther from the sun than the Earth.

Jupiter is one of the four planets named the Jovian planets. The other three Jovian planets are Saturn, Neptune, and Uranus. Pluto is the only planet farther from the sun than the Jovian planets.  Jupiter’s atmosphere is composed of helium and hydrogen. The Giant Red Spot was discovered in the seventeenth century. The mass of Jupiter is 2.5 times the mass of all the other planets combined. The proportion to its volume, however, is much less. Its density is less than the Earth’s.   

There are many more moons than the twelve we thought Jupiter had in the 1960s. A recent estimate was there are 63 moons revolving around Jupiter. Jupiter takes only ten hours to spin on its axis compared to twenty-four hours for the Earth. The escape velocity is 133,200 miles per hour compared to 25,009 miles per hour for Earth. Jupiter's atmosphere is about 86% hydrogen and 14% helium with traces of other gases.

There are four planet-sized moons circling Jupiter named Ganymede, Europa, Io, and Callisto. They are also known as the Galilean Satellites because they were first seen by Galileo when he invented the telescope in 1610.

Io is volcanically solar system. Callisto is the second largest moon of Jupiter and third largest in the solar system. Europa has a frozen crust, and Callisto’s crust is icy. Twenty-three new moons were discovered in 2003. The outer moons of Jupiter might be asteroids swept in by Jupiter's atmosphere. Io's atmosphere has sulphur dioxide. Europa’s has oxygen, Ganymede’s also has oxygen, and Callisto’s has carbon dioxide. The factthat Europa and Ganymede have atmospheres containing oxygen means they have one of the

requirements for the possibility of life existing on the moons. The names of some of the other moons of Jupiter are Almalthea, Himalia, Elara, Pasiphae, Sinope, Lysithea, Carme,

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