eli5: Today NASA announced it has detected a gas on a planet 120 light years away that might indicate life. How?

Question

I just can’t compute how this is possible. How can a telescope detect a gas, which isn’t even visible to the naked eye, on a planet that is an incomprehensible distance away.

[Source](https://www.bbc.co.uk/news/science-environment-66786611)

In: 143

Answer 1

Each element eats up a certain colour in the rainbow. So we can look at the light coming in from a planets atmosphere, divide the light up into a rainbow using something like a prism, and check which colours are missing. We use that like a chemistry map to tell us which elements the planet is made out of.