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

Astronomers have examined Gliese 367 b, a neighboring sub-Earth exoplanet, with the James Webb Space Telescope (JWST). The data collected suggest that this extraterrestrial globe is hot, black, and devoid of any discernible atmosphere. The updated results were made available on the pre-print service arXiv on January 2.

Known by the Tahay name, Gliese 367 b (or GJ 367 b) was found in December 2021 using NASA's Transiting Exoplanet Survey Satellite (TESS). It revolves around Gliese 367, sometimes called Añañuca—an M-dwarf of spectral type M1.0V that is around 31 light years distant and has a mass and size that is over half that of the sun. At least two more planets, situated farther out from the host, are also present in the system.

Gliese 367 b's mass is estimated to be 0.67 Earth masses, meaning it is around 30% smaller than Earth, according to earlier measurements. At 1,367 K, its equilibrium temperature, it orbits its parent star once every 7.7 hours.

The atmosphere of Gliese 367 b has now been studied by a group of astronomers led by Michael Zhang of the University of Chicago using JWST's Mid-Infrared Instrument (MIRI). Further information about this exoplanet's characteristics and nature was provided by the observations.

"We monitored GJ 367 b for 12.7 h, corresponding to 1.6 planetary orbits, using the Mid-Infrared Instrument on JWST," the researchers stated in their report.

Based on the data, Gliese 367 b is a planet with a blackbody emission spectra in the MIRI bandpass, a dark surface, and no discernible atmosphere or heat redistribution. Gliese 367 b was discovered to have a daytime temperature of 1,728 K and an estimated nighttime temperature of less than 847 K.

The findings, as reported in the publication, rule out the likelihood that Gliese 367 b contains an atmosphere of carbon dioxide at a pressure higher than one bar. Additionally, it does not include an outgassed atmosphere under severely oxidizing circumstances or one that is expelled under heavily reducing conditions with a pressure of more than 10 millibar.

Based on the available information, Gliese 367 b is expected to have a mostly molten dayside. As a result, any volatiles in this planet's silicate mantle ought presumably be distributed among the atmosphere. Because of this, the paper's authors came to the conclusion that, barring a volatile-free mass, Gliese 367 b must not have an atmosphere.

Based on the findings, the scientists further hypothesize that Gliese 367 b's apparent absence of atmosphere suggests that the planet contains a lot less volatiles overall than Earth. They speculate that the absence of atmosphere may result from strong star irradiation eliminating the early volatiles.