James Webb Space Telescope Spots Water Vapor on Distant Exoplanet

Astronomers could be on the verge of a major breakthrough in the search for extraterrestrial life.

Using the James Webb Space Telescope (JWST), scientists spotted water vapor around a distant exoplanet(Opens in a new window), known as GJ 486 b. The only problem is, they can't tell if it came from the rocky world or its cool host star.

"Water vapor in an atmosphere on a hot rocky planet would represent a major breakthrough for exoplanet science," according to(Opens in a new window) the program's principal investigator, Kevin Stevenson, of the Johns Hopkins University Applied Physics Lab (APL). "But we must be careful and make sure that the star is not the culprit."

Some 30% larger than our planet, and three times as massive, GJ 486 b transits its red dwarf star, crossing in front of it (from our viewpoint). If an atmosphere does exist, the Space Telescope Science Institute explains, starlight would filter through its gases to create "fingerprints" in the light, allowing astronomers to decode its composition.

"We see a signal and it's almost certainly due to water," lead study author Sarah Moran said in a statement. "But we can't tell yet if that water is part of the planet's atmosphere, meaning the planet has an atmosphere, or if we're just seeing a water signature coming from the star."

While the water vapor could indicate the presence of an atmosphere on GJ 486 b, it's equally plausible it came from the exoplanet's host star, which is much cooler than the Sun, and concentrates even more water vapor within its starspots.

Though the scientists didn't observe the planet crossing any starspots during transits, they could still exist elsewhere on the star. "And that's exactly the physical scenario that would imprint this water signal into the data and could wind up looking like a planetary atmosphere," according to study co-author Ryan MacDonald.

If present, a water vapor atmosphere would gradually erode, due to stellar heating and irradiation, and require constant replenishing from steam-spewing volcanoes.

Future observations using Webb's Mid-Infrared Instrument (MIRI) and Near-Infrared Imager and Slitless Spectrograph (NIRISS) are required to shed more light on this potential system.

"It's joining multiple instruments together that will really pin down whether or not this planet has an atmosphere," Stevenson said.

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