Gliese 1252b, a super-Earth exoplanet that orbits an M-dwarf star 67 light-years away, retains only a tenuous mineral exosphere.
An artist’s impression of the super-Earth Gliese 1252b and its parent star. Image credit: Sci.News.
Gliese 1252 is an M3-type dwarf (red dwarf) star approximately 67 light-years from Earth in the constellation of Telescopium.
Also known as GJ 1252, TIC 370133522, TOI-1078, L 210-70 and LHS 492, the star has a mass 38% that of the Sun, a radius 39% that of the Sun, and an apparent magnitude of 12.2.
Gliese 1252 hosts a terrestrial planet that is about 1.2 times bigger than Earth and 2.1 times as massive.
First discovered in 2019 and named Gliese 1252b, the alien world orbits the star once every 12.4 hours at a distance of only 0.009 AU (astronomical units).
“The pressure from Gliese 1252’s radiation is immense, enough to blow a planet’s atmosphere away,” said Dr. Michelle Hill, an astrophysicist at the University of California Riverside.
“Earth also loses some of its atmosphere over time because of the Sun, but volcanic emissions and other carbon cycling processes make the loss barely noticeable by helping replenish what is lost.”
“However, in greater proximity to a star, a planet cannot keep replenishing the amount being lost.”
“In our Solar System, this is the fate of Mercury. It does have an atmosphere, but one that is extremely thin, made up of atoms blasted off its surface by the Sun. The extreme heat of the planet causes these atoms to escape into space.”
To determine that Gliese 1252b lacks an atmosphere, Dr. Hill and colleagues measured infrared radiation from the planet as its light was obscured during a secondary eclipse.
This type of eclipse occurs when a planet passes behind a star and the planet’s light, as well as light reflected from its star, is blocked.
The radiation revealed the planet’s scorching daytime temperatures, estimated to reach 1,410 K (1,137 degrees Celsius, or 2,079 degrees Fahrenheit) — so hot that gold, silver, and copper would all melt on the planet.
The heat, coupled with assumed low surface pressure, led the astronomers to believe there’s no atmosphere.
Even with a tremendous amount of carbon dioxide, which traps heat, the researchers concluded Gliese 1252b would still not be able to hold on to an atmosphere.
“Gliese 1252b could have 700 times more carbon than Earth has, and it still wouldn’t have an atmosphere. It would build up initially, but then taper off and erode away,” said Dr. Stephen Kane, an astrophysicist at the University of California Riverside.
“M-dwarf stars tend to have more flares and activity than the Sun, further reducing the likelihood that planets closely surrounding them could hold on to their atmospheres.”
“It’s possible this planet’s condition could be a bad sign for planets even further away from this type of star,” Dr. Hill said.
“This is something we’ll learn from the NASA/ESA/CSA James Webb Space Telescope, which will be looking at planets like these.”
There are 5,000 stars in the solar neighborhood, most of them M-dwarfs. Even if planets orbiting them can be ruled out entirely, there are still roughly 1,000 stars similar to the Sun that could be habitable.
“If a planet is far enough away from an M-dwarf, it could potentially retain an atmosphere. We cannot conclude yet that all rocky planets around these stars get reduced to Mercury’s fate. I remain optimistic,” Dr. Hill said.
The study was published in the Astrophysical Journal Letters.
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Ian J.M. Crossfield et al. 2022. GJ 1252b: A Hot Terrestrial Super-Earth with No Atmosphere. ApJL 937, L17; doi: 10.3847/2041-8213/ac886b
