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 finding means that many of the planets orbiting these stars may also lack atmospheres and are therefore unlikely to harbor living things.
The work that led to the revelations about the planet without an atmosphere, named GJ 1252b, is detailed in the Astrophysical Journal Letters.
This planet orbits its star twice in 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 and inhospitable.
“The star’s radiation pressure is immense, enough to blow away a planet’s atmosphere,” said Michelle Hill, a UC Riverside astrophysicist and co-author of the study.
Earth also loses some of its atmosphere over time to the sun, but volcanic emissions and other carbon cycle processes make the loss barely noticeable by helping to replenish what is lost. However, closer to a star, a planet cannot continue to replenish the lost amount.
In our solar system, this is the fate of Mercury. It has an atmosphere, but extremely fine, composed of atoms expelled from its surface by the sun. The planet’s extreme heat causes these atoms to escape into space.
To determine that GJ 1252b has no atmosphere, astronomers measured the planet’s infrared radiation as its light was obscured during a secondary eclipse. This type of eclipse occurs when a planet passes behind a star and light from the planet, as well as light reflected from its star, is blocked.
The radiation revealed the planet’s scorching daytime temperatures, estimated at 2,242 degrees Fahrenheit, so hot that gold, silver and copper would all melt on the planet. The heat, coupled with a supposedly low surface pressure, has led researchers to believe that there is no atmosphere.
Even with a huge amount of carbon dioxide, which traps heat, the researchers concluded that GJ 1252b would still not be able to hold an atmosphere. “The planet could have 700 times more carbon than Earth, and it still wouldn’t have an atmosphere. It would initially build up, then shrink and erode,” said Stephen Kane, UCR astrophysicist and co-author of the study.
M dwarf stars tend to have more brightness and activity than the sun, which further reduces the likelihood that planets that closely surround them can retain their atmosphere.
“It’s possible that the state of this planet is a bad sign for planets even further away from this type of star,” Hill said. “That’s something we’ll learn from the James Webb Space Telescope, which will observe 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 which are M dwarfs. Even though the planets orbiting them can be entirely ruled out, there are still about 1,000 sun-like stars that could be habitable.
“If a planet is far enough away from an M dwarf, it could potentially retain an atmosphere. We cannot yet conclude that all rocky planets around these stars are reduced to Mercury’s fate,” Hill said. “I remain optimistic.”
Rapid destruction of Earth-like atmospheres by young stars
Ian JM Crossfield et al, GJ 1252b: A hot terrestrial super-earth without an atmosphere, Letters from the Astrophysical Journal (2022). DOI: 10.3847/2041-8213/ac886b
Provided by University of California – Riverside
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