Jupiter, named after the King of the Roman Gods and ruler of Mount Olympus, is the largest planet in our solar system. Its mass is about 318 times that of Earth, and its volume is over 1,330 times greater. It has more mass than the other eight planets combined.
Jupiter has sixteen known satellites. The four largest are Io, Europa, Ganymede and Callisto. These four moons are called the Galilean moons for their discoverer, Galileo Galilei. All of the Galilean moons except Europa are bigger than the Earth's Moon in diameter. Ganymede, the largest of all the moons, is bigger than the planet Mercury.

Jupiter and its moons are currently probed by two NASA spacecrafts, Galileo and Cassini. Cassini on its journey to Saturn was closest to Jupiter on December 30th, 2000. One important discovery made by Cassini was Jupiter's magnetosphere, an ionized-gas bubble encasing the planet, is lopsided and leaky, with an unexpected abundance of high-energy particles bleeding out of one side.

In December 2000, the Hubble Space Telescope captured images of a curtain of glowing gas is wrapped around Jupiter's north pole like a lasso. This curtain of light, called an aurora, is produced when high-energy electrons race along the planet's magnetic field and into the upper atmosphere where they excite atmospheric gases, causing them to glow.

Where is Jupiter?

Solar System Simulator updated every 5 minutes, courtesy of JPL, NASA. The orbits of the Earth and Jupiter are shown here, and they are moving in a counterclockwise direction. Click on picture to enlarge view.

Jupiter can be seen with the naked eye from earth. To locate Jupiter in your night sky, check here for guide.

Jupiter has a very low density because it is made mostly from light gases such as hydrogen and helium. The swirls of color that can be seen on Jupiter are actually concentrations of gas called cloud belts. Jupiter spins on its axis very quickly, as do the other giant planets. However, Jupiter doesn't spin in one synchronized motion. Like the Sun, it rotates differentially. It takes longer for certain spots on the planet to revolve around Jupiter's axis than at other points.

There is a large magnetic field around Jupiter. This field is not circular; it's like a giant windsock pointed away from the sun. Interactions with solar winds cause changes in the size of the magnetosphere. Seven of Jupiter's moons reside inside the boundaries of the magnetosphere.

	The Jupiter System A family portrait of the Jupiter System showing Galilean moons Io, Europa, Ganymede, Callisto. 800 x 600 pixels 1024 x 768 pixels
	Jupiter's Clouds This 1979 Voyager image uses enhanced color to show light-colored, ascending clouds and dark, descending bands. 800 x 600 pixels 1024 x 768 pixels
	Clouds up close This color-enhanced image was assembled from three Voyager 1 black-and white negatives. 800 x 600 pixels 1024 x 768 pixels
	Great Red Spot Jupiter's largest storm, with winds far stronger than the worst hurricane on Earth, is seen from 3.72 million miles (6 million km) away by Voyager 2. 800 x 600 pixels 1024 x 768 pixels
	Closeup on Io Jupiter's most volatile moon, Io and the Great Red Spot as seen by Cassini during December 2000 flyby on its way to Saturn. 800 x 600 pixels 1024 x 768 pixels