Astronomers could soon be tracking down exoplanets with liquid water oceans not by looking for the presence of water, but instead by searching for the absence of carbon dioxide in their atmospheres.
The search for habitable planets beyond our Solar System has been governed by the search for liquid water in space, but there are no observatories that can detect surface water directly.
However, space telescopes such as the James Webb Space Telescope are able to observe carbon dioxide in a planet’s atmosphere.
"On Earth, much of the atmospheric carbon dioxide has been sequestered in sea water and solid rock, which has helped to regulate climate and habitability for billions of years," says Frieder Klein from Woods Hole Oceanographic Institution, who took part in the study alongside astronomers from MIT.
This means our planet has significantly less carbon dioxide in its atmosphere than the similarly sized Venus and Mars.
By looking for extrasolar systems with several similarly sized terrestrial planets, it could be possible to spot one where a water ocean has absorbed most of the carbon dioxide from the atmosphere.
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