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

Scientists analyze the light reflected from the planet and compare that result to that of pure, known gases on Earth. When the analyses match perfectly, they know the gas on the other planet matches the one they tested on earth.