Jupiter

Jupiter is the largest planet in the Solar System—so massive that it contains over 70% of the planetary mass of the Solar System. Made mostly of hydrogen and helium, Jupiter is classified as a gas giant with no solid surface.

Its atmosphere is a swirling mix of colorful cloud bands, storms, and jet streams. The most famous feature is the Great Red Spot, a gigantic storm larger than Earth that has been raging for centuries. Wind speeds on Jupiter can exceed 600 km/h (370 mph).

Jupiter has a powerful magnetic field—the strongest of any planet—creating enormous radiation belts and intense auroras at its poles. Surrounding Jupiter is a faint ring system made of dust particles.

With over 95 known moons, Jupiter has a miniature planetary system of its own. The four largest, known as the Galilean moons, each have unique features:

• Io: the most volcanically active body in the Solar System.
  
  

• Europa: believed to have a global subsurface ocean beneath its icy crust.
  
  

• Ganymede: the largest moon in the Solar System, even bigger than Mercury.
  
  

• Callisto: an ancient, heavily cratered world with a mysterious underground ocean.
  
  

These moons make Jupiter one of the most important targets in the search for extraterrestrial life.