Composition of Jupiter

Jupiter's density is about 1.3 times that of water. So even though we know that Jupiter has a heavy element core, we know that the composition of Jupiter is mostly hydrogen and helium like the Sun. The outer layers of Jupiter are the lighter elements, like hydrogen and helium.

Jupiter itself is about 78% molecular hydrogen (H₂) and 19% helium with trace amounts of methane (CH₄), ammonia (NH₃) and water (H₂O). The pressure on Jupiter is so great that the gases which are gas at normal pressure and temperatures on Earth are liquid on Jupiter. Really deep in the interior, something even stranger happens to hydrogren. Not only is it liquid, but it becomes something called liquid metallic hydrogen. Metallic hydrogen just means that the molecules are organized in such a way that the atoms share electrons easily, allowing the liquid hydrogen to be electrically conductive. Try that with normal liquid hydrogen (though there really isn't anything normal about liquid hydrogen because it needs to be at 14 Kelvin (-253°C or -423°F) to be liquid. Obviously, liquid metallic hydrogen does not occur naturally on Earth, but can be created in labs under the correct pressure and temperature conditions.

The outer layers of Jupiter are its atmosphere which is "only" 1000 km thick, but that is only 1% of Jupiter's radius of 72,000 km. Compare that to Earth which has an atmosphere that is 2.5% of the Earth's radius. The atmosphere is composed of hydrogen gas with different cloud layers. The topmost cloud layer is ammonia crystals at a temperature of 150K, followed by ammonia hydrosulfide at 200 K, with the lowest cloud layer being water at 280K. The Galileo probe, whose images have been included in some of these posts, was also used to explore the atmosphere of Jupiter. After entering the atmosphere, the probe reached darkness about 80km down and was completely destroyed by the high pressure and heat at only 130 km down.