Planets orbiting the most common star may be uninhabitable

Since M dwarfs are ubiquitous, this finding means that many planets orbiting these stars may also lack atmospheres and are therefore unlikely to harbor living organisms.

The work that led to the detection of a planet without an atmosphere, called GJ 1252b, is detailed in Astrophysical Journal Letters.

This planet orbits its star twice in one day on Earth. It is slightly larger than Earth and is closer to its star than Earth to the Sun, making GJ 1252b extremely hot and inhospitable.

“The star’s radiation pressure is enormous, enough to blow up the planet’s atmosphere,” said Michelle Hill, an astrophysicist at the University of California, Riverside, 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 make up for what’s lost. However, near the star, the planet cannot continue to replenish the lost amount.

In our solar system, this is the fate of Mercury. It has an atmosphere, but it is very soft, made up of atoms that the sun has expelled from its surface. The planet’s intense 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 blocked out during a secondary eclipse. This type of eclipse occurs when a planet passes behind a star and the light from the planet is blocked, as is the reflected light from its star.

The radiation revealed the planet’s scorching daytime temperatures, estimated at 2,242 degrees Fahrenheit — so hot that the planet’s gold, silver and copper would melt. The heat, along with the supposedly low surface pressure, led researchers to believe there was no atmosphere.

Even with the massive amount of carbon dioxide, which traps heat, the researchers concluded that GJ 1252b was still unable to retain the atmosphere. The planet could have 700 times more carbon than Earth, and it wouldn’t have an atmosphere. “It will build up at first, then decline and erode,” said Stephen Kane, an astrophysicist at the University of California, and co-author of the study.

M dwarf stars tend to be brighter and more energetic than the Sun, making it less likely that planets that closely surround them retain their atmospheres.

“It’s possible that the state of this planet is a bad sign for planets far from this type of star,” Hill said. “This is something we will learn from the James Webb Space Telescope, which will monitor planets like these.”

Hill’s work on this project was supported by a grant from NASA’s Future Investigators Program on Earth and Space Science and Technology.

The research was led by Ian Crossfield of the University of Kansas. It included scientists from the University of California Riverside, NASA’s Jet Propulsion Laboratory, California Institute of Technology, University of Maryland, Carnegie Institution for Science, Max Planck Institute for Astronomy, McGill University, University of New Mexico and University of Montreal.

There are 5,000 stars in Earth’s solar neighborhood, most of which are M dwarfs. Although the planets orbiting them can be ruled out completely, there are still about 1,000 potentially habitable Sun-like stars.

“If a planet were far enough away from the M dwarf, it would probably retain an atmosphere. We cannot yet conclude that all the rocky planets around these stars are the fate of Mercury,” Hill said. »