Jupiter, the largest known planet in our solar system, is a big mystery to us. We can see it in our telescopes, even the naked eye sometimes, and we've sent probes right past it and around its moons, but we don't really know much about it at all. From analysing its mass and size we can make some guesses about what it's made of and how it formed, but until we send a probe into it we can only make educated guesses. However, what our educated guesses tell us is pretty cool.
Our current estimate is that the core of Jupiter, probably about 60,000 km across, is made of tightly compacted elements, probably similar to rock, although a lot denser. A bit like the solid core of the Earth, the pressure and gravity of Jupiter's core is likely to be an unknown substance (in the sense that we've never seen anything like it directly on Earth so have no idea what it would look like).
Surrounding that is probably my favourite layer, a sphere of liquid metal Hydrogen. The idea of liquid metal Hydrogen is so strange and unlike anything we've ever seen that my mind starts bending at the thought of it. If you've ever seen a zeppelin or a Hydrogen balloon you know that Hydrogen is normally a very sparse gas, lighter than air. Now imagine it somehow turning into a metal? Just mind-blowing. Not only that, but it's a rotating core of liquid metal which means the entire planet probably conducts electricity.
Coating this is a layer of liquid Hydrogen (a bit like liquid Nitrogen, just less dense) and then finally a thin layer of Hydrogen gas. The inner cores of Jupiter are probably rotating and grinding against each other which leads to changes in temperature and pressure. These changes affect what happens on the next layer out and so on, until what we see on the surface of Jupiter (the atmosphere) is one constant lump of storm. A storm-ball floating in space surrounding layers of liquid metal hydrogen and hyper-dense rock. So what happens inside Jupiter's atmosphere? Weird, weird things!