Spectroscopy can identify planets capable of supporting life. Note the differences between the spectroscopic data of these three solar system planets; Mars, Earth, and Venus. Dips indicate varying types of gases in their atmospheres. Although all three planets show a significant dip in the spectroscopic data for carbon dioxide, only Earth clearly shows the presence of water, ozone, and carbon dioxide.
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NASA, ESA, CSA, Christine Klicka (STScI)
