Like the sun, Jupiter is composed predominantly of hydrogen & helium. But unlike the sun, it lacks the necessary amount to begin fusion, the process that fuels a star. Jupiter would need to be 75-80 times more massive than it is at present to be considered a star. If all of the planets in the solar system had formed as part of the gas giant, it still would not have sufficient mass. Still, by itself, Jupiter is 2 & 1/2 times larger than all of the other planets in the solar system combined.
PHOTOS: Spectacular Views Of The Solar System's Moons
Callisto, Jupiter's moon-Spectacular! According to NASA, it has the darkest surface of the four Galilean moons, but is twice as bright as our moon :) It is also the most heavily cratered object in the entire solar system!
Ganymede A satellite of Jupiter and the largest moon in the Solar System. It is the seventh moon and third Galilean satellite outward from Jupiter. Completing an orbit in roughly seven days, Ganymede participates in a 1:2:4 orbital resonance with the moons Europa and Io, respectively.
Rare Triple Eclipse On Jupiter - Five spots – one colored white, one blue, and three black – are scattered across the upper half of the planet. The spots are actually a rare alignment of three of Jupiter's largest moons – Io, Ganymede, and Callisto – across the planet's face - Hubble Space Telescope