With the help of the James Webb Space Telescope, a research team detects water vapor around an exoplanet. Does the rocky planet have an atmosphere?

Baltimore – The James Webb Space Telescope (JWST) looks deep into the universe and uses its infrared gaze to discover things that other telescopes before it have not been able to detect. The latest discovery of the ten billion US dollar telescope: JWST has detected water vapor around a rocky planet. The exoplanet, called GJ 486 b, is located 26 light-years from Earth and orbits a red dwarf star once every 1.5 days.

Actually, the exoplanet is too close to its star to be in the habitable zone – the region where liquid water is possible on the planet's surface. Its surface is a piping hot 430 degrees Celsius, so the planet is too hot to be habitable. Nevertheless, the "Webb" observation suggests that there could be water vapor there – a possible indication of an atmosphere surrounding the planet.

"James Webb" telescope finds water vapor – an indication of an atmosphere?

Water vapor has so far only been detected outside our solar system in gaseous planets. If researchers can prove that there is indeed water vapor around GJ 486 b, this would be an important discovery. After all, they could use it to prove that the planet is similar to Earth and Mars in many ways. "Water vapor in an atmosphere around a hot rocky planet would be a major breakthrough for exoplanet research," explains Kevin Stevenson, who works at the Webb telescope. However, he also emphasizes: "We have to be careful and make sure that the star is not the culprit."

Artist's impression: The exoplanet GJ 486 b orbits a red dwarf star. © NASA, ESA, CSA, Joseph Olmsted (STScI), Leah Hustak (STScI)

What the scientist means by this: Researchers know that water vapor occurs in the cooler sunspots on our sun. Because the red dwarf star orbiting GJ 486b is cooler than our Sun, there could be even more water vapor in the sunspots — and such a signal in the "Webb" data could be misinterpreted as water vapor surrounding the planet.

Signal points to water around exoplanet GJ 486 b

"We're seeing a signal, and it's almost certainly due to water. But we can't yet say if this water is part of the planet's atmosphere, which means that the planet has an atmosphere, or if we just see a water signature coming from the star," explains Sarah Moran (University of Arizona) in a statement. Moran is the lead author of a study on the find, which was accepted for publication in The Astrophysical Journal Letters.

Moran's research team used the Webb telescope to observe two so-called "transits" of the exoplanet: The exoplanet passes in front of its star, the star's light is filtered through the planet's atmosphere and can reveal the components of the atmosphere. "We didn't see any evidence that the planet crossed starspots during its transits," says Ryan MacDonald (University of Michigan), emphasizing, "But that doesn't mean there aren't spots elsewhere on the star." It is precisely through this scenario that the water signature could have entered the planet's data, the researcher knows.

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James Webb telescope to provide more information about exoplanets

So is the discovery of water vapor actually an indication of an exoplanet's atmosphere? Researchers assume that an atmosphere around a hot planet like GJ 486 b would have to be permanently replenished – for example, by steam from volcanoes. In order to find out more about the potential atmosphere around the exoplanet, "Webb" will re-examine the celestial body. "By combining several instruments, it will be possible to determine whether this planet has an atmosphere or not," explains Stevenson. (tab)