The planet Jupiter, named after the Roman king of the gods, has been a notable astronomical object since ancient times. Galileo's observations of Jupiter and its moons in 1610 helped provide important evidence for the heliocentric theory of planetary motion. Although this outer planet is hundreds of millions of miles from Earth at closest approach, it is still easily visible as a bright, colored point in the night sky.
Overview and Facts
The gas giant Jupiter is the largest planet in the solar system, more than 300 times more massive than Earth. Due to its enormous size and reflective clouds, Jupiter is the third brightest object in the night sky, after the moon and Venus. At a distance of about 500 million miles from the sun, Jupiter orbits just outside the asteroid belt. Because of the large distance, one Jupiter year is equivalent to nearly 12 Earth years.
Like other gaseous planets, Jupiter lacks a solid, rocky surface. Instead, the planet is composed of gaseous layers that grow increasingly dense with greater depth. In fact, the weight is so intense that deep within Jupiter, hydrogen is compressed into a metallic liquid that conducts electricity. This liquid is the source of Jupiter's magnetic field. Chemically, Jupiter is 90 percent hydrogen and 10 percent helium, with trace amounts of ammonia and other substances that give the planet its vivid colors.
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Although Saturn's rings are more well-known, Jupiter is also surrounded by flat rings of debris. Jupiter's ring system is smaller and closer to the planet than Saturn's and contains mostly small grains of rock and dust. Because these rings contain no ice, they are not brilliant and reflective like Saturn's rings, and thus were only discovered in 1979 by the Voyager 1 spacecraft.
Great Red Spot
Jupiter's entire visible surface is covered by clouds, many of which are composed of ammonia gas. These clouds are stretched into stripes by strong winds in the planet's atmosphere. The Great Red Spot, a particularly notable red blotch in the southern hemisphere of the planet, is a giant, high-pressure storm that has been raging for more than 300 years.
More than 60 known satellites, or moons, orbit the planet Jupiter. Some satellites are very small and have temporary, chaotic orbits. Other satellites are large and stable, like the four moons discovered by Galileo: Io, Europa, Ganymede and Callisto. These moons are almost as large as planets, and have complex layered structures that resemble our own Earth. Past and future space missions aim to investigate the geography of Jupiter's moons and search for liquid water or even life.