Space and Time
Size: Diameter 143,844km
Mass: 1.898x10(exp27)kg
Composition: Possible small core of iron and rock
Mean temperature: -123 °c
Distance from Sun: 778.3 million km
Atmosphere/weather: Mostly hydrogen and helium
Moon/satellites: Over 50
Orbital length: 4332.6 days
Length of day: 59 hours, 55 minutes
Distance from Earth: Max 928 million km, min 628 million km
Jupiter is the fifth planet from the Sun and the first and largest of the gas giants. With its many moons and several rings, Jupiter can be described as being at the centre of its own mini-solar system. Jupiter is the most massive planet in our solar system and in composition it resembles a small star. Jupiter is more than twice as massive as the other eight planets combined.
At first glance, Jupiter appears striped. These stripes are dark belts and light zones created by strong east-west winds in Jupiter's upper atmosphere. Within these belts and zones are storm systems that have raged for years. The southern hemisphere's Great Red Spot has existed for at least 100 years, perhaps longer, as Galileo reported seeing a similar feature nearly 400 years ago. Three Earths could fit across the Great Red Spot. Jupiter's core may not be solid but a dense, hot liquid with a consistency like thick soup. The pressure inside Jupiter may be 30 million times greater than the pressure at Earth's surface.
Jupiter's striped atmosphere. The Great Red Spot is clearly visible
Unknown until 1979 when they were discovered NASA's Voyager 1 spacecraft, Jupiter's rings were a surprise. A flattened main ring and an inner cloud-like ring, called the halo, are both composed of small, dark particles. A third ring, known as the gossamer ring because of its transparency, is actually three rings of microscopic debris from three small moons: Amalthea, Thebe and Adrastea. Jupiter's ring system may be formed by dust kicked up as interplanetary meteoroids smash into the giant planet's four small inner moons. The main ring probably comes from the tiny moon Metis.
In December 1995, NASA's Galileo spacecraft dropped a probe into Jupiter's atmosphere. Carrying six scientific instruments, the probe survived the crushing pressure and searing heat for nearly an hour. It collected the first direct measurements of Jupiter's atmosphere, the first real data about the chemistry of a gas planet. Following the release of the probe, the Galileo spacecraft began a multi-year orbit of Jupiter, observing each of the largest moons from close range several times.
Montage of Jupiter and the Galilean satellites, Io, Europa, Ganymede and Callisto.
In 1610, Italian astronomer Galileo Galilei was surprised to see four small 'stars' near Jupiter. He had discovered Jupiter's four largest moons, now called Io, Europa, Ganymede and Callisto. Collectively, these four moons are known today as the Galilean satellites.
The Galilean satellites
Io is the most volcanically active body in our solar system. Ganymede is the largest planetary moon and has its own magnetic field. A liquid ocean may lie beneath the frozen crust of Europa. An icy ocean may also lie beneath the crust of Callisto. As recently as February 2003, astronomers discovered 12 new moons orbiting the giant planet. Jupiter now officially has 52 moons - the most in the solar system. Many of the outer moons are probably asteroids captured by the giant planet's gravity.
View an animation of the Voyager spacecraft flying by Io and Jupiter based on images taken during the Voyager program. Courtesy of NASA Voyager Project
Jupiter was the Roman king of the gods and patron of the Roman state. He was also known as Jove. In Greek mythology he was Zeus and lived on Mount Olympus. Many of Jupiter's moons are named after other figures in the life of Zeus, particularly his lovers.
Images, information and videos courtesy of NASA.