Jupiter, one of the Gas Giants
Jupiter is the largest planet in our solar system and is one of the "gas giants". Jupiter has various moons and a ring system. In 1610 Galileo Galilei discovered Jupiter's four largest moons - Io, Europa, Ganymede and Callisto. These moons are known as 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. In 2003 alone, astronomers discovered 23 new moons orbiting the planet. Jupiter now officially has 63 moons - the most in the solar system. Many of the outer moons are believed to be asteroids captured by the giant planet's gravity.

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, and 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 is probably not 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 rings were discovered in 1979 by NASA's Voyager 1 spacecraft. The flattened main ring and an inner cloud-like ring, called the halo, are both composed of small, dark particles. A third ring, the gossamer ring, 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.

Jupiter orbits around the Sun at an average distance of 778,412,020 km. It takes Jupiter 4331 Earth days to complete its orbit around the Sun. A day on Jupiter will be just 9.925 hours long with an effective temperature of -148 C.

Jupiter: Facts & Figures

  • Average Distance from the Sun: Metric: 778,412,020 km
  • Perihelion (closest): 740,742,600 km
  • Aphelion (farthest): 816,081,400 km
  • Equatorial Radius: 71,492 km
  • Equatorial Circumference: 449,197 km
  • Mass: 1,898,700,000,000,000,000,000,000,000 kg
  • Volume: 1,425,500,000,000,000 km3
  • Density: 1.33 g/cm3
  • Surface Area: 62,179,600,000 km2
  • Equatorial Surface Gravity: 20.87 m/s2
  • Escape Velocity: 214,300 km/h
  • Length of Day: 9.925 hours
  • Length of Year: 4330.6 Earth days (11.8565 Earth years)
  • Mean Orbit Velocity: 47,051 km/h
  • Orbital Eccentricity: .04839
  • Orbital Inclination to Ecliptic: 1.305 degrees
  • Equatorial Inclination to Orbit: 3.12 degrees
  • Orbital Circumference: Metric: 4,774,000,000 km
  • Effective Temperature: -148 °C
  • Atmospheric Constituents: Hydrogen, Helium
  • Number of Moons: 63

Source: NASA