Jupiter has a long history of surprising scientists – all the way back to 1610 when Galileo Galilei found the first moons beyond Earth. That discovery changed the way we see the universe. Fifth in line from the Sun, Jupiter is, by far, the largest planet in the solar system – more than twice as massive as all the other planets combined.
Jupiter is made up almost entirely of hydrogen and helium. On the surface of Jupiter–and on Earth–those elements are gases. However inside Jupiter, hydrogen can be a liquid, or even a kind of metal. These changes happen because of the tremendous temperatures and pressures found at the core.
The composition of Jupiter is similar to that of the Sun – mostly hydrogen and helium. Deep in the atmosphere, pressure and temperature increase, compressing the hydrogen gas into a liquid. This gives Jupiter the largest ocean in the solar system – an ocean made of hydrogen instead of water.