Jupiter, along with its beautiful ringed sister planet, Saturn, are the gas-giant duo of our Sun's family of eight major planets. The other two giant planets--that dwell in our Solar System's outer limits--are Uranus and Neptune. Uranus and Neptune are classified as ice giants, because they carry within them larger cores than Jupiter and Saturn, as well as thinner gaseous envelopes. Jupiter and Saturn may (or may not) contain small, hidden cores, that are heavily veiled by extremely massive, dense gaseous envelopes.
Jupiter is circled by a bewitching duo of moons that are potentially capable of nurturing delicate tidbits of life as we know it. Like its more famous sister-moon, Europa, Ganymede might harbor a life-loving subsurface ocean of liquid water in contact with a rocky seafloor. This special arrangement would make possible a bubbling cauldron of fascinating chemical reactions--and these reactions could potentially include the same kind that allowed life to evolve on our own planet!
A moon is defined as a natural satellite in orbit around another body that, in turn, is in orbit around its Star. The moon is kept in its position by both its own gravity, as well as its host's gravitational grip. Some planets have many moons, some have only a small number, and still others have none at all. Several asteroids inhabiting our Solar System are circled by very small moons, and some dwarf planets--such as Pluto--also host moons.