Jupiter
DISTANCE FROM SUN: 484 million miles (778 million kilometers).
REVOLUTION AROUND SUN: 11.86 years.
ROTATION: 9.9 hours.
DIAMETER: 88,750 miles (142,800 kilometers).
DENSITY: 1.3 x that of water.
MASS: 318 x that of Earth.
SURFACE TEMPERATURE: -236°F (-149°C) at cloud tops.
Satellites (closest to most distant):
Adrastea
Metis
Amalthea
Thebe
Io
Europa
Ganymede
Callisto
Leda
Himalia
Lysithea
Elara
Ananke
Carme
Pasipahe
Sinope
Moving outward from the sun, the realm of the gas giants begins with the biggest of them all. Jupiter contains nearly all the planetary material in the solar system. It if were a hollow ball, Jupiter could contain more than one thousand Earths.
With 16 moons coursing around it, the Jupiter system resembles a miniature sun with planets. Some scientists have called Jupiter a “failed sun” although it would have to be 65 to 80 times more massive to ignite and sustain nuclear reactions like a star. Like the sun, Jupiter is mostly hydrogen and helium.
Jupiter has no solid surface, but we see an outer layer of clouds arranged in colorful bands around the planet by the action of high-speed jet streams. The patterns can change within hours, but for the past three centuries, at least, there has been one constant: Jupiter’s Great Red Spot. The spot is actually a complex storm, an anticyclone spinning typhoon-like in a counterclockwise direction.
Scientists have recently discovered that Jupiter has its own aurora, similar to those on Earth. While Earth’s aurora are triggered by disturbances of electrified particles in the incoming solar wind, Jupiter’s seem to be caused both by processes in the planet’s radiation belts and by particles shed by its volcanic moon Io. Observers have also seen lightning bolts blast from among Jupiter’s clouds.

MOONS AND RINGS The first known moons of another world were those of Jupiter, sighted by Galileo Galilei nearly 400 years ago. He saw four; further observations from Earth-based telescopes and spacecraft have increased the known number to at least 16.
Io, the first known actively volcanic place besides Earth, has mountains that spew plumes of gas and dust hundreds of miles into space before they gently arc back to the surface, drawn by the moon’s weak gravity. Some volcanoes that were inactive when Voyager 1 first sent back images in 1979 have now come to life.
The Galileo spacecraft has revealed the moon Europa to be a possible water world; an object with an unseen ocean, topped with a fractured sheet of ice. The moon also has a trace atmosphere of molecular oxygen, making it only the fourth object in the solar system to have oxygen in its atmosphere (along with Earth, Mars, and Venus). But don’t look for any oxygen-breathing life forms on the surface. If all the oxygen on Europa were compressed to the surface pressure of Earth’s atmosphere, it would fill only a dozen stadiums the size of Houston’s Astrodome.
If there is liquid water under Europa’s ice, it is probably warmed by tidal forces created by Jupiter’s enormous gravitational pull.
Jupiter’s ring is comprised of three segments—the main ring, the halo, and the Gossimer ring—primarily made of dust from two of the planet’s four small inner moons.

SPOTS AND STREAKS The solar system’s storm of the century—and of the past two centuries, as well—is Jupiter’s Great Red Spot. This anticyclone in the planet’s southern hemisphere, which appears red due to sunlight reflecting off high clouds, rotates completely every six days or so. And while cloud motion appears to be minor at the center, a chaotic collection of smaller storms and eddies churns farther out.
A series of smaller storms have been sighted on Jupiter by Earth-based observers since the 1930s, and more recently by both the Hubble Space Telescope and the Galileo orbiter. In the centers of these cloud systems air rises, carrying fresh ammonia gas upward. New ice crystals form when the upwelling gas freezes as it reaches the chilly cloud top level, where temperatures are -236°F (-149°C).
The storms often divert, but seldom interrupt, horizontal bands of cloud movement that streak across the planet’s disk. Cloud patterns on the surface can change dramatically within just a few hours.

COMET SHOEMAKER-LEVY 9 IMPACT For six days in July 1994, fragments of the comet Shoemaker-Levy 9 crashed into Jupiter. The comet, which was in orbit around Jupiter, had broken up under the planet’s massive gravitational pull.
The impacts sprayed debris over Jupiter’s clouds, creating a series of black “bullseyes” that rotated across the planet’s face for days. Following one of the larger fragment impacts, unusual auroras appeared some 70,000 miles (113,000 kilometers) away, and at the northern mid-latitudes where such aurora are rarely observed.