How to Find Life: When starlight passes through a planet’s atmosphere, certain elements absorb specific wavelengths of light, and these show up as dips in the spectrum. McKibillo
If aliens are out there, the best shot at finding them—assuming they resemble the life-forms on Earth—is to look for planets like ours. E.T.’s home will probably require an atmosphere to have liquid water and keep out solar radiation, so astronomers search for perfectly sized and situated planets surrounded by blankets of life-supporting gases like oxygen and water vapor. Now they know how to recognize that ideal atmosphere.