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The James Webb Space Telescope has spotted water vapor around a rocky exoplanet orbiting a star 26 light-years from Earth.
Now astronomers are trying to determine if this water vapor is an indicator of what would be the first known presence of an atmosphere around a rocky exoplanet.
Small, cool red dwarf stars are the most common stars in the universe. The exoplanets found in the “habitable zone” — the perfect distance from a star for the planet to be warm enough to host liquid water on its surface — often orbit very closely to red dwarfs, as they are not as warm as the are sun.
Red dwarf stars lash out with ultraviolet and X-ray radiation that has the potential to destroy fragile layers of gas, leading scientists to question whether rocky planets that orbit them can maintain — or regain — atmospheres.
Astronomers observed a hot, rocky exoplanet called GJ 486 b with the Webb telescope. The planet is about 30% larger than Earth and has a much stronger surface gravity than our planet.
The planet is so close to its parent star that GJ 486 b orbits it once every 1.5 Earth days, and this proximity heats the planet to a surface temperature of 800 degrees Fahrenheit (430 degrees Celsius). Astronomers believe the planet is tidally dependent, meaning one side is always facing the star while the other is a permanent night side – similar to how the moon orbits Earth.
Although scorching temperatures are making the planet too hot to be habitable, observations of GJ 486 b with Webb’s near-infrared spectrograph showed evidence of water vapor. A study detailing the findings has been accepted for publication in The Astrophysical Journal Letters.
The presence of water vapor may indicate that GJ 486 b somehow has an atmosphere, despite its heat and proximity to the star.
While water vapor has already been detected on gaseous exoplanets, scientists have yet to find an atmosphere around a rocky exoplanet — this would be a milestone, as it would make it somewhat resemble planets in our solar system, such as Earth and Mars, that are thought to be rocky.
“Water vapor in an atmosphere on a hot, rocky planet would be a major breakthrough for exoplanet research. But we have to be careful and make sure the star isn’t the culprit,” study co-author Kevin Stevenson, principal investigator for the Webb observing program at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland, said in a statement.
The team observing GJ 486 b watched the planet pass in front of its star twice, then used multiple methods to analyze the data collected by the telescope’s instruments.
When planets pass in front of their stars, also known as a transit, starlight can penetrate a planet’s atmosphere and highlight the chemical traces of various gases and elements. Webb data analysis results indicated that water vapor was present around GJ 486 b.
But astronomers are cautious about their interpretation of the results because it’s possible the water vapor is associated with the star itself.
“We’re seeing a signal, and it’s almost certainly water. But we can’t yet tell if this 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,” said study lead author Sarah Moran. postdoctoral researcher at the University of Arizona in Tucson, in a statement.
Even on our Sun, there is water vapor in sunspot regions. Sunspots, or starspots, are areas that appear dark on stars because they are cooler than other parts of the surface.
Because the red dwarf star hosting GJ 486 b is much smaller and cooler than the Sun, it may contain even more water vapor in its starspots – enough to produce a signal that could be misinterpreted as a planetary atmosphere narrowing the range orbiting exoplanets, the researchers said the researchers.
“We have observed no evidence that the planet has crossed any starspots during transits. But that doesn’t mean there aren’t spots elsewhere on the star. And that’s exactly the physical scenario that would imprint this water signal into the data and could end up looking like a planetary atmosphere,” study co-author Ryan MacDonald, a NASA Sagan Fellow at the University of Michigan at Ann Arbor, said in a statement.
The star’s heat and radiation would likely erode GJ 486 b’s potential atmosphere over time. If the exoplanet currently has an atmosphere, it would need to be replenished from a constant source, such as vapor from volcanoes.
Future observations of the planet using various Webb telescope instruments could reveal additional details about the source of the water vapor.
“It connects several instruments that really determine whether or not this planet has an atmosphere,” Stevenson said.
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