Average distance from the Sun: 5.203 AU (778.33
million km)
Orbital period (Length of Year): 11.86 Earth years
Rotational period (Length of Day): 9.8 Earth hours
Orbital inclination: 1.3 deg
Average orbital speed around the Sun: 13.07 km/s
Diameter: 142,800 km
Axial inclination: 3.08 deg
Mass: 1.90 x 10 ^ 27 kg (317.7 Earth masses)
Relative surface gravity (Earth = 1): 2.364
Average temperature: -153 deg C (-243 deg F)
Atmosphere: hydrogen, helium, methane
Albedo: 0.44
Number of moons: 61
Jupiter is the largest planet in the solar system - larger than all the other
planets combined. Through a telescope you can see cloud bands in its atmosphere
and its four large Galilean satellites (moons), so named because they were
discovered by Galileo in 1610. The moons look like little stars strung out on
either side of the planet, lined up with Jupiter's equator. They can be seen to
shift their positions after just a few hours as they orbit around Jupiter.
We usually think of the Jupiter's primary elements, hydrogen and helium, as gases. However, at a depth of a few thousand kilometers below the surface, these elements turn to liquid. Most of the planet's mass is in fact in a liquid state. Thus, Jupiter should be considered a liquid planet rather than a gas planet, as it is often called. Because the planet is mostly fluid, and because it spins very quickly, it is not a perfectly spherical planet. Rather, it bulges around the equator.
Jupiter radiates about twice as much energy as it receives from the Sun. Astronomers believe that the energy is being released by gravitational forces as Jupiter continues to contract slightly (perhaps as little as 1 millimeter per year), or that it is simply still losing heat built up during its formation.
In 1979, when the sophisticated Voyager 1 and 2 spacecraft flew past Jupiter, we received astonishing pictures and data, including striking photographs of Jupiter's swirling, turbulent mass of clouds and storms. The most interesting feature of the visible cloud "surface" is the Great Red Spot, a huge, spinning, anticyclone so large that it takes six Earth-days to complete one turn. One could place at least two Earths across this spot. It is a relatively stable feature, having first been observed 300 years ago. Sometimes the Spot is quite prominent, though the color will sometimes fade and even disappear for a few years. Astronomers have speculated that the Spot is the whirlpool of a violent, long-lasting storm, similar to an Earthly hurricane. On Earth, such storms fade quickly from friction with land as they move over continents. However, on Jupiter, there are no land masses, so such storms could last for centuries.
The four Galilean satellites also held big surprises for the Voyager spacecraft scientists. Mysterious Io, orbiting in Jupiter's intense electromagnetic field, was most remarkable. Its red, orange, and yellow surface is full of many spectacular erupting volcanoes. Icy Europa is crisscrossed by streaks, which close pictures suggest are flat, filled-in cracks in the crust. Darker Ganymede, the largest moon in the solar system, is bigger than the planets Mercury and Pluto, and has icy craters of all sizes, as well as masses of shifted fault lines similar to those caused by quakes on Earth. Callisto, also dark and icy, is covered with small and medium sized craters and one huge impact that left "ripples" in its crust. Callisto may be the most heavily-cratered body in the solar system. The Voyagers also looked at the tiny reddish moon Amalthea, which appears to be the most oblong moon in the solar system. Amalthea is about twice as long as it is wide.
The spacecraft discovered another surprise: a thin ring of rocky debris around Jupiter which is too faint to be seen in Earth-bound telescopes. The ring is just a few miles thick and its particles orbit Jupiter along with the inner moons, about 57,000 kilometers (34,000 miles) above the cloud tops. The material on the inside of the ring may actually stretch all the way down to the clouds.
Data and pictures from the Pioneer and Voyager missions have revealed the presence of several additional tiny moons, bringing Jupiter's current known moon count to sixteen.
In 1993, amateur astronomers Eugene and Carolyn Shoemaker and David Levy discovered a comet which appeared to be heading for a collision with Jupiter. Interestingly by the time it was discovered, the comet was actually in orbit around Jupiter rather than the Sun. The collision would mark the first time humans have predicted and witnessed a collision by two bodies in space. It was an extraordinary opportunity to learn about collisions in space, and about Jupiter and comets as well. Shoemaker-Levy 9, as the comet was soon named, broke into a couple dozen pieces before the collision, due to Jupiter's strong gravity. Instead of just one collision, scientists would get to see a series of collisions of varying size!
The collisions took place on July 16 - 22, 1994. Practically every large ground-based telescope was aimed at the giant planet. Several space probes, such as the Hubble Space Telescope and the Galileo probe headed for Jupiter, were well placed to observe the collisions. Even Voyager 2, which had long since left the solar system, took images of the event.
The collisions were more spectacular than anyone had expected. Some of the most energetic impacts left very dark spots even larger and more noticeable than the Great Red Spot. As Jupiter rotated over the next several months, the dark spots spread out int o dark bands around the planet. The last bits of evidence of the collision disappeared from the planet by late 1995.
Photos courtesy: NASA. Photos (L-R): Jupiter, close-up of Jupiter's Red Spot, montage of Jupiter and some of its moons.
Information Source: http://www.moreheadplanetarium.org/index.cfm