Gliese 367 b is a dark, hot sub-Earth with no atmosphere, study finds

Using the James Webb Space Telescope (JWST), astronomers studied a nearby sub-Earth exoplanet known as Gliese 367 b. The results obtained indicate that this extraterrestrial world is dark, hot and devoid of detectable atmosphere. The new results were published on January 2 on the preprint server arXiv.

Gliese 367 b (or GJ 367 b for short, nicknamed Tahay) was discovered in December 2021 with NASA’s Transiting Exoplanet Survey Satellite (TESS). It orbits Gliese 367 (also known as Añañuca), an M dwarf of spectral type M1.0V located about 31 light years away, almost half the size and mass of the sun. The system is also home to at least two other planets, located further away from the host.

Previous observations of Gliese 367 b revealed that it is about 30% smaller than Earth and has a mass of about 0.67 Earth masses. It has an equilibrium temperature of 1,367 K and circles its parent star every 7.7 hours.

Now, a team of astronomers led by Michael Zhang of the University of Chicago used JWST’s Mid-Infrared Instrument (MIRI) to characterize the atmosphere of Gliese 367 b. The observations allowed us to better understand the properties and nature of this exoplanet.

“Using the JWST mid-infrared instrument, we monitored GJ 367 b for 12.7 hours, which corresponds to 1.6 planetary orbits,” the researchers wrote in the paper.

Observations revealed that Gliese 367 b is a planet with no detectable atmosphere, no heat redistribution, and a dark surface in the MIRI bandwidth with a black body emission spectrum. Gliese 367 b’s daytime temperature was found to be 1,728 K, while its nighttime temperature was estimated to be less than 847 K.

According to the article, the results exclude the possibility that Gliese 367 b had a carbon dioxide atmosphere with a pressure above 1 bar. This also excludes a degassed atmosphere with a pressure greater than 10 millibars (under strongly reducing conditions) or an degassed atmosphere with a pressure greater than 0.01 millibar (under strongly oxidizing conditions).

The data collected suggests that Gliese 367 b should have a largely molten dayside. Therefore, all volatile elements present in the silicate mantle of this planet should be released into the atmosphere. This is why the authors of the paper concluded that Gliese 367 b must have no atmosphere, unless its mass is free of volatile substances.

Additionally, based on the results, the researchers speculate that the lack of atmosphere observed at Gliese 367 b indicates that the planet contains considerably fewer volatiles as a whole than Earth. They assume that this lack of atmosphere may be due to the elimination of initial volatile substances by intense stellar irradiation.

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