GJ 367b is another dead world orbiting a red dwarf star, astronomers say

The habitability of red dwarf exoplanets is a hot topic in space science. These small, dim stars are home to many exoplanets, including small rocky planets about the size of Earth. However, this small star emits extremely powerful flares that can damage or strip away its atmosphere.

If we want to understand the habitability of red dwarfs, we need to understand the atmospheres of the exoplanets that orbit them.

In a new study, astronomers studied the atmosphere of the oft-mentioned exoplanet GJ 367b and found nothing. The planet likely lost all its volatile matter a long time ago, and the reason for this is the red dwarf star orbiting Earth.

Gliese 367 is a red dwarf star (M dwarf) located about 30 light-years away that has three known exoplanets orbiting it. Astronomers discovered GJ 367b and its sibling planet in 2021 with NASA’s TESS (Transiting Exoplanet Survey Satellite). GJ 367b is an extremely short-period planet, taking only 7.7 hours to orbit once, and is likely tidally locked to its star. Because it is so close to the red dwarf star, it receives hundreds of times more radiation than Earth receives from the Sun. All of the radiation blasting its surface means its daytime temperature is about 1,500°C (1,770 K; 2,730°F).

GJ 367b is a sub-Earth with a radius of approximately 72% that of Earth. However, its density is extremely high, almost twice that of Earth. Scientists believe it is mostly iron, with the outer silicate layer stripped away. It is also called the iron planet.

Exoplanets around red dwarf stars are easy to spot because they are very faint and small compared to other stars. This helps find planets with both the transit method and the radial velocity method. Therefore, it makes sense to study both, since there are so many of them that we can see.

In a new, unpublished paper, researchers used the James Webb Space Telescope’s Mid-Infrared Imaging Instrument (MIRI) to examine GJ 367b. The paper states, “GJ 367b is a dark, hot, airless subterranean region of Earth.” Currently in preprint, Posted to arXiv The author is Michael Zhang, a postdoctoral fellow in the Department of Astronomy and Astrophysics at the University of Chicago.

Although the paper’s title suggests a conclusion, the details are interesting.

GJ 367b was never habitable because it is too close to its star. However, astronomers are very interested in exoplanets orbiting red dwarf stars (M dwarfs). First, there are many red dwarfs. Half of the stars in the Milky Way are probably red dwarfs, and probably much more. Therefore, most of the exoplanets in our galaxy likely orbit red dwarfs, and planet hunters have discovered an abundance of exoplanets around red dwarfs.

“The question of whether small rocky planets orbiting M dwarfs can retain an atmosphere is of paramount importance for habitability,” the authors write. Because red dwarfs are dim and small, red dwarfs are easier to study than stars similar to the Sun. Larger, brighter stars like our sun could drown out an exoplanet’s atmosphere. But when it comes to the potential habitability of red dwarf exoplanets, an elephant has crept into the room: flares.

“However, it has long been suggested that M dwarfs’ high-energy radiation, flares, and long premain sequences strip planets of their atmospheres. The extent to which this occurs is the subject of active research.” They explain.

The reason it is such an active area of ​​research is that the fundamental mechanisms behind atmospheric formation are poorly understood. There are two mechanisms. The release of volatiles during planet formation and the release of volatiles as young magma ocean planets cool and solidify. Further research is needed on two mechanisms for stripping the atmosphere: photoevaporation and stellar wind erosion.

There’s a lot to learn, and that’s what this research is slowly moving forward with. “By observing M dwarf planets and determining their host atmospheres, if any, we can construct a sample of empirical benchmarks that can be used to calibrate atmospheric mass loss models,” the authors write. clearly stated.

Researchers examined GJ 367b’s daytime emission spectrum to determine what its surface is made of and what kind of atmosphere, if any, is present, even if it is thin and tenuous. I checked to see if there is. They concluded that the planet had zero albedo, no heat recycling, and no atmosphere.

“GJ 367b is the first sub-Earth surface observation to be performed,” Zhang and his co-authors wrote. “These observations reveal a planet with no detectable atmosphere, no heat redistribution, and a dark surface within the MIRI band (A_B ≈ 0.1), using the blackbody emission spectrum.

“The lack of heat redistribution excludes ≳ 1 bar atmospheres over a wide range of compositions, but the emission spectrum also excludes even thinner atmospheres at some compositions,” the authors explain. For comparison, Earth’s atmosphere is about 1 bar at sea level.

It’s no surprise that GJ 367b lacks atmosphere. That’s because it lies on the so-called “cosmic coastline.” The cosmic coastline is a metaphor for the statistical trends that connect all the planets. This is the dividing line that appears when comparing the light a planet receives from a star to how easily the planet’s atmosphere can escape into space.

“The lack of an atmosphere is not surprising given the planet’s location far above the ‘cosmic coastline,’ but it is not the best news for the prospects for atmospheric measurements of M-dwarf rocky planets.” They explain.

GJ 367b was never habitable. It’s too close to that star. But it’s still important data that can help scientists better understand exoplanet atmospheres in general. And more similar data is needed to understand the habitability of red dwarfs.

“If there are rocky planets orbiting M-type dwarfs, we recommend using JWST to observe planets near or below the coastline of the universe in order to understand which rocky planets have atmospheres.” ” conclude the authors.

So what are the prospects for habitability of M dwarfs? There is growing evidence that red dwarfs do not make good company when it comes to the habitability of exoplanets. It’s so dark that the habitable zone is much closer. This means that an exoplanet in a red dwarf’s habitable zone will be exposed to intense flares that can destroy its atmosphere and bombard its surface with intense radiation.