ATMOSPHERE

The atmosphere near the surface of Jupiter is about 88 to 92% hydrogen, 8 to 12% helium, and 1% other gases.

The lower atmosphere is so heated and the pressure so high that helium changes to liquid form. It rains down onto the planet. Based on spectroscopy, Jupiter seems to be made of the same gases as Saturn. It is different from Neptune or Uranus. These two planets have much less hydrogen and helium gas.

The very high temperatures and pressures in Jupiter's core mean scientists cannot tell what materials would be there. This cannot be found out, because it is not possible to create the same amount of pressure on Earth.

Above the unknown inner core is an outer core. The outer core of Jupiter is thick, liquid hydrogen. The pressure is high enough to make the hydrogen solid, but then it melts because of the heat.

The planet Jupiter is sometimes called a failed star because it is made of the same elements (hydrogen and helium) as is the Sun, but it is not large enough to have the internal pressure and temperature to cause fusion, which is the energy source that powers the sun and most other stars.