Question: how would we know if a distant planet had an earth like atmosphere?

Grant Kennedy answered on 18 Mar 2013:

Great question! There is a lot of research going on right now that’s trying to answer this very question. In every case we need to get the spectrum of the planet, which means taking the light and splitting it up into different wavelengths so we know how much there is of each colour.

Detecting an atmosphere is VERY hard, we can do it for a few distant planets that are a bit like Jupiter, but that orbit even closer than Mercury. So these planets have huge atmospheres compared to Earth-like planets, making them easier to detect. We’ve found things like methane, carbon dioxide, and even water in their atmospheres. We’ll be able to do these tests for Earth-like planets some day, but for now it’s too hard and we need better technology.

Other methods want to look for signs of life directly rather than looking at just the atmosphere, like looking for signs of plant life because they absorb lots of visible light, but reflect infrared light. We haven’t been able to try this one out on another planet yet, but at least we have some ideas of what to look for when we can!

g