system
Given the following post, respond as if you're commenting on Reddit:
human
Does Jupiter have a solid core of anything or is it truly just a large ball of gas?
gpt
So first off...

> is it truly just a large ball of gas?

We know for sure that this is not true. At the pressures and temperature in the interior of Jupiter, hydrogen turns into a liquid metal. In fact, by mass, Jupiter is *mostly* liquid metallic hydrogen. It's also the only thing that can explain Jupiter's incredibly strong magnetic field.

Now, to address your original question...

> Does Jupiter have a solid core of anything

This is a major question in the field right now, and one of the primary mission goals of the Juno spacecraft. There's still a lot of questions whether the liquid metallic hydrogen forms a mantle surrounding a solid core. Based on what we think we know about how giant planets form, though, we're pretty sure there's needs to be a core...or at least there used to be one.

Jupiter formed out past the "snow line" - the distance from the Sun where it's cold enough that water is stable as ice. This is important, because if you're a growing proto-planet, you can grow a lot faster out past the snow line using both ice and rock, rather than the planets that formed inside the snow line which formed from just rock alone. You need to hit a mass of about 5 to 10 Earth-masses before you have sufficient gravity to start holding on to hydrogen gas.

Our current hypothesis is that Jupiter's core is somewhere around 10 - 30 Earth-masses (compared to a total mass of 318 Earth-masses), and it's made of rock and exotic ices. Note that even though the temperatures are very high at the center of Jupiter, the pressure is so extreme that water will be solid, forming unusual crystal arrangements of ice.

Now there is a vocal minority of scientists who believe that Jupiter has no core at all. Some think it's because it formed from gas collapse instead of the more commonly-accepted core accretion theory outlined above. In the gas collapse scenario, the collective self-gravity of an extra-dense clump of hydrogen gas in the protoplanetary disk collapsed in on itself to form the planet. However, most of our models indicate there just wasn't enough time for that collapse to happen before the Sun ignited and blew all the gas away.

A few others think Jupiter used to have a core, but no longer. Again, surrounding this hypothesized rocky icy core is a massive mantle of liquid metallic hydrogen. Thing is, most of our models indicate that liquid metallic hydrogen is a very good solvent (we've only been able to produce metallic hydrogen in the lab pretty recently and only for a split-second, so most of our assumptions about the stuff come from computer simulations). If it turns out to be a good enough solvent, then it could actually have dissolved a 20 Earth-mass rocky icy core over the lifetime of the Solar System.

**TL;DR**: Probably. It's definitely *not* just a ball of gas, though, as it's mostly liquid metal.