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| Illustration of a red dwarf star orbited by a hypothetical exoplanet. Red dwarfs erupt with intense flares that could strip a nearby planet's atmosphere over time, or make the surface inhospitable to life as we know it. Credit: NASA/ESA/STScI/G. Bacon |
An Earth-like planet orbiting an M dwarf—the most common type of star in the
universe—appears to have no atmosphere at all. This discovery could cause a
major shift in the search for life on other planets.
Because M-dwarfs are so ubiquitous, this discovery means a large number of
planets orbiting these stars may also lack atmospheres and therefore are
unlikely to harbor living things.
The work that led to the revelations about the no-atmosphere planet, named
GJ 1252b, are detailed in the Astrophysical Journal Letters.
This planet orbits its star twice during the course of a single day on
Earth. It is slightly larger than Earth, and it is much closer to its star
than Earth is to the sun, making GJ 1252b intensely hot as well as
inhospitable.
"The pressure from the star's radiation is immense, enough to blow a
planet's atmosphere away," said Michelle Hill, UC Riverside astrophysicist
and study co-author.
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 GJ 1252b lacks an atmosphere, astronomers 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 2,242 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 researchers to believe there's no atmosphere.
Even with a tremendous amount of carbon dioxide, which traps heat, the
researchers concluded GJ 1252b would still not be able to hold on to an
atmosphere. "The planet 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 Stephen Kane, UCR astrophysicist and study
co-author.
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," Hill said. "This is something we'll
learn from the James Webb Space Telescope, which will be looking at planets
like these."
Hill's work on this project was supported by a grant from the Future
Investigators in NASA Earth and Space Science and Technology program.
There are 5,000 stars in Earth's 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," Hill said. "I remain optimistic."
Reference:
Ian J. M. Crossfield et al, GJ 1252b: A Hot Terrestrial Super-Earth with No
Atmosphere, The Astrophysical Journal Letters (2022).
DOI: 10.3847/2041-8213/ac886b
Tags:
Space & Astrophysics