Jupiter is the largest planet in the Solar System. It is a gas giant with a mass roughly 318 times that of Earth, more than two and a half times the mass of all the other planets in the Solar System combined. Despite its enormous size, Jupiter is not solid: it is composed mainly of hydrogen and helium, with no well-defined surface. Pressure and temperature rise steadily with depth until the gas gradually transitions into a hot, dense liquid metallic hydrogen interior.

The most recognizable feature of Jupiter is the Great Red Spot, a vast storm larger than Earth that has persisted for at least 350 years. The planet's banded appearance comes from fast-moving belts and zones of cloud driven by powerful jet streams. Jupiter rotates faster than any other planet, completing a day in just under ten hours, which flattens it noticeably at the poles.

Jupiter has a large family of moons, including the four large Galilean moons discovered by Galileo in 1610: Io, Europa, Ganymede, and Callisto. Ganymede is the largest moon in the Solar System and is bigger than the planet Mercury. Europa is of particular scientific interest because it is thought to hold a subsurface ocean of liquid water beneath its icy crust, making it a target in the search for life beyond Earth.
