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Planetary composition and characteristics

Jupiter is the fifth planet from the Sun and by far the largest. It is a giant planet, whose mass is 318 times that of Earth.

Jupiter is about 90% hydrogen and 10% helium (by numbers of atoms, 75/25% by mass). The atmosphere contains trace amounts of:

  • methane
  • water vapor
  • ammonia
  • silicon-based compounds

There are also traces of carbon, ethane, hydrogen sulfide, neon, oxygen, phosphine, and sulfur. The outermost layer of the atmosphere contains crystals of frozen ammonia. This is very close to the composition of the primordial Solar Nebula from which the entire solar system was formed.

The interior contains denser materials - by mass it is roughly 71% hydrogen, 24% helium, and 5% other elements. Through infrared and ultraviolet measurements, trace amounts of benzene and other hydrocarbons have also been found. Although the core of Jupiter might be composed of heavier elements, Jupiter lacks a well-defined solid surface like the other giant planets.

Moons (satellites) of Jupiter

Jupiter has 69 known natural satellites. Of these, 53 are less than 10 kilometres in diameter and have only been discovered since 1975.

The four largest moons, visible from Earth with binoculars on a clear night, known as the "Galilean moons", are:

  • Io
  • Europa
  • Ganymede
  • Callisto
Jupiter and moon Europa (shadow). Credits NASA/JPL/University of Arizona.
Jupiter and the four Galilean moons. Credits NASA/JPL/DLR