Illustration of the exoplanet Gliese 367 b. It's a strange planet, probably composed entirely of iron. Its red dwarf may have stripped itself of its outer silicate layer and atmosphere. **nasa
The habitability of red dwarf extragalactic planets is a hot topic in space science. These dim, small stars are home to many exoplanets, including small, rocky planets the size of Earth. But these small stars emit extremely powerful flares that can destroy and strip the atmosphere.
If we are to understand the habitability of red dwarfs, we need to understand the atmospheres of exoplanets orbiting them.
In a new study, astronomers studied the atmosphere of the oft-mentioned exoplanet GJ 367b, and found nothing. The planet may have lost any volatiles it had long ago, and its orbiting red dwarf star is to blame.
Gliese 367 is a red dwarf (m dwarf) located about 30 light-years from Earth, and there are three known exoplanets orbiting it. Astronomers discovered GJ 367B and its siblings in 2021 using NASA's TESS (Transiting Exoplanet Survey Satellite). GJ 367b is an ultra-short-period planet that takes only 7An orbit can be completed in 7 hours and is likely to be tidally locked to its star. It is so close to the red dwarf that it receives hundreds of times more radiation than the Earth receives from the Sun. All radiation blasts on their surface imply a daytime temperature of about 1,500 °C (1,770 K; 2,730°f）。
GJ 367b is a sub-Earth with a radius of about 72% of the Earth's radius. But it is very dense, almost twice as dense as the Earth. Scientists believe that it is mainly iron, and its outer silicate layer has been stripped away. It is sometimes referred to as the Iron Planet.
Exoplanets are easier to spot around red dwarfs than other stars because they are fainter and smaller. This helps to find planets using the transit method and the radial velocity method. Therefore, it makes sense to study them because there are so many of them, and we can see so much.
In a new, unpublished article, researchers examined GJ 367B with the mid-infrared instrument (MIRI) of the James Webb Space Telescope. This ** is "GJ 367b is a dark, hot, airless underground earth". It is now in preprint, posted on the ARXIV server, by Michael Zhang, a postdoctoral researcher in the Department of Astronomy and Astrophysics at the University of Chicago.
The title of this ** gives the conclusion, but the details are interesting.
GJ 367B will never be habitable because it is too close to its star. But astronomers are very interested in exoplanets orbiting red dwarfs (m dwarfs). On the one hand, red dwarfs are numerous;Half of the stars in the Milky Way are probably red dwarfs, perhaps much more than that. As a result, most of the exoplanets in our galaxy probably orbit red dwarfs, and planet hunters have discovered a large number of exoplanets around them.
The question of whether a small rocky planet orbiting a m dwarf can accommodate an atmosphere is crucial for habitability," the authors write. Red dwarfs are easier to study than sun-like stars because red dwarfs are fainter and smaller. Larger, brighter stars like our Sun can submerge exoplanets' atmospheres. But when it comes to the potential habitability of red dwarf exoplanets, an elephant has crept into the room: a flare.
However, it has long been believed that the high-energy radiation, flares, and long pre-main sequence banded planet atmospheres of m-dwarf stars;The extent to which this happens is the subject of active research," the researcher explained.
The reason why it is such an active area of research is that little is known about the basic mechanisms behind the creation of the atmosphere. There are two mechanisms: volatile transfer during planet formation and volatile release when young magmatic ocean planets cool and solidify. There are also two mechanisms by which the atmosphere can be stripped away, and they also require more research: light evaporation and stellar wind erosion.
There's a lot to learn, and that's what this research is cutting down. "By looking at the m-dwarf planets and determining which host atmospheres, if any, we can build an empirical benchmark sample that can be used to calibrate atmospheric mass loss models," the authors clearly and unambiguously stated.
The researchers examined GJ 367B dayside emission spectra to determine what the surface is made of and, if any, what type of atmosphere, if any, exists, even if it is just a thin and fragile layer. They concluded that the planet has zero albedo, no thermal recirculation, and no atmosphere.
GJ 367b is the first sub-Earth with thermal surface observations," Zhang and his co-authors wrote. "These observations reveal a planet with no detectable atmosphere, no heat redistribution, and a dark surface in the MIRI bandpass (ab 0.).1) Has a blackbody emission spectrum.
"The lack of heat redistribution excludes 1 bar of atmospheric pressure for various components, while the emission spectrum excludes a rarer atmosphere for some components," the authors explain. In comparison, the Earth's atmosphere is about 1 bar at sea level.
It's no surprise that GJ 367B lacks atmosphere. That's because it's located above the so-called "cosmic coastline". The cosmic coastline is a metaphor for the statistical trends that connect all the planets together. A dividing line emerges when we compare the light that a planet receives from its star with how easy it is for the planet's atmosphere to escape into space.
Whereas, the planet is much higher'Cosmic coastline', the lack of an atmosphere is not surprising, although it is not the best news for the prospects of measuring the atmospheres of mm dwarf rock planets, "the author explains.
GJ 367B will never be habitable. It's too close to its star. But this is still important data that will help scientists better understand the atmospheres of exoplanets. If we are to understand the habitability of red dwarfs, we need more data like this.
We encourage JWST to make observations of planets near or below the cosmic coastline to understand which, if any, rocky planets orbiting the m dwarf star have atmospheres," the authors concluded.
So what is the prospect of a habitable m dwarf?There is growing evidence that red dwarfs are not very good bed-sharing in terms of the habitability of exoplanets. Since they are very dim, their habitable area is much closer. This means that exoplanets in the habitable zone of red dwarfs are subjected to intense flares that damage the atmosphere and bathe their surfaces in intense radiation.
More information: Michael Zhang et al., GJ 367b is a dark, hot, airless underground Earth, Arxiv (2024). doi： 10.48550/arxiv.2401.01400