Jupiter is the largest planet in the solar system, with a diameter of about 139,820 km — roughly 11 times wider than Earth.
Jupiter is a gas giant made mostly of hydrogen and helium, and it's more than twice as massive as every other planet in the solar system combined. Its volume alone could hold over 1,300 Earths.
Jupiter formed early in the solar system's history, in a region beyond the "frost line" where ice and gas could accumulate freely. Its strong gravity let it pull in enormous amounts of hydrogen and helium from the surrounding disk of material, well before the Sun's radiation cleared that material away.
Jupiter also has the strongest magnetic field of any planet and the most moons confirmed so far — over 90, including the four large Galilean moons (Io, Europa, Ganymede, and Callisto) that Galileo observed in 1610.
Last reviewed: September 2026