Next, they’ll use the spectrograph to try to find key molecules like oxygen or methane. How much they find of each determines what they’ll look for next, like carbon dioxide or ozone. (Photosynthesis, which could arise on other worlds, produces oxygen. Organisms that use oxygen typically produce carbon dioxide and water, while some kinds of microbes, like bacteria, produce methane.)
It’s best to estimate all of these potential biosignatures, if possible, and not just one. But depending on the wavelength range a telescope’s spectrograph is sensitive to, it will be able to measure the abundance of some molecules better than others. Charting all these paths on Young’s decision tree will tell
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