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Journalism of Courage
The exoplanet GJ 486 b is a rocky world like Earth that is about 30 per cent larger and about three times as massive. It orbits a red dwarf star very closely, with a “year” on the planet taking about 1.5 Earth days. It is too close to be within the “habitable zone” for a planet but the James Webb Space Telescope seems to have found hints of water.
GJ 486 b orbits so close to the star that its surface temperature must be around 430 degrees Celsius, according to the Space Telescope Science Institute (STScI). But despite this, Webb has found hints of water vapour in the planet’s system. This water vapour could be coming from the planet’s atmosphere but more observations will be needed to determine if the planet actually has an atmosphere in the first place.
If the planet does have an atmosphere and that is where the water was detected, it would need to continuously replenished because of losses due to radiation from the star. Another plausible explanation is that this water vapour is actually from the outer layer of the planet’s relatively cool host star. Webb will have to make additional observations to help astronomers answer this question.
Red Dwarf star, or M-dwarfs, are believed to be the most common type of star in the universe, according to Smithsonian Magazine. They are quite small and are not much more voluminous than a gas giant planet. They also have relatively low mass and temperature for a star. The smallest red dwarfs have only about 80 times the mass of Jupiter. For context, our Sun is about 1,000 times more massive than Jupiter.
Red dwarf stars are also relatively cooler. This means that a planet staying in a tight orbit might just be warm enough to host liquid water. But at the same time, such stars are quite active, especially when they are young. They release ultraviolet and X-ray radiation that could destroy the planetary atmosphere.
This is why the question of whether a rocky planet could maintain or even reestablish an atmosphere is an important question for astronomers. Scientists turned to GJ 486 b to answer this question.
Despite being too close to its host star to be in the habitable zone, Webb’s NIRSpect (Near-Infraref Spectrograph) detected hints of water. If the water vapour detected is on the planet, this could mean that it has an atmosphere despite its scorching temperatures and close proximity to its star.
STScI says that water vapour has been detected on gaseous exoplanets before but to date, astronomers have not been able to definitively detect an atmosphere around a rocky exoplanet.
While that does sound exciting, researchers caution that the water detected by Webb could also be from the star itself. “We didn’t observe evidence of the planet crossing any starspots during the transits. But that doesn’t mean that 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 wind up looking like a planetary atmosphere,” said Ryan MacDonald, co-author of the study, in a press statement.
The study documenting the presence of water on the planet has been accepted for publication in the Astrophysical Journal Letters.
While it may sound like a long shot, the water vapour originating from the star is actually a very plausible explanation. Interestingly, even in our own Sun, water vapour can sometimes exist in sunspots since these regions are much cooler compared to other parts of the star’s surface.
Also, GJ 486 b’s host star is much cooler than the Sun so there is the possibility of much more water vapour concentrating within its starspots. If such water vapour is present, it could create a signal similar to the presence of a planetary atmosphere.
