Peering at a rocky planet 26 light-years away, the James Webb Space Telescope (JWST) has spied signs of water vapor. The discovery would mark the first time that astronomers have ever managed to discern an atmosphere on a rocky planet outside our own solar system. Finding water vapor on a small world would also be a major step forward in the search for habitable planets beyond Earth because water is essential to life as we know it.
An equally likely explanation for the water vapor has thrown ambiguity into the potentially milestone result, however. Spots of magnetic activity on the planet’s host star could just as well be the water vapor’s source. Ultimately untangling the mystery will require further observations with a variety of instruments.
“Just knowing that water could exist on a rocky planet around another star would be a huge deal,” says Ryan MacDonald, an astrophysicist at the University of Michigan. At the same time, he says, “in science, it’s good to play a bit of devil’s advocate” rather than overpromise a result that turns out to be incorrect. A preprint paper detailing MacDonald and his colleagues’ analysis of the water vapor was posted on May 1, and the study has been accepted for publication in the Astrophysical Journal Letters.
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