ElI5: how do they know what other planets are made off, how can the be so sure? Jupiter could be made of a completely unknown gas?

Question

ElI5: how do they know what other planets are made off, how can the be so sure? Jupiter could be made of a completely unknown gas?

In: 96

Answer 1

Also I’d like to point out that there are no “unknown” gasses. We know every element in the periodic table and “unknown” ones would not be stable enough to exist in a steady state.