Neighboring super-Earth has sulfur-rich atmosphere, Webb’s observations suggest

Using the James Webb Space Telescope (JWST), astronomers at the Space Telescope Science Institute (STScI) in Baltimore, Maryland, and elsewhere have performed transmission spectroscopy of a nearby super-Earth exoplanet known as L98-59 d. The results of these observations, available in a research paper published August 28 on the preprint server arXivsuggest that the planet has a sulfur-rich atmosphere.

L98-59 is a bright M dwarf star located about 34.6 light-years from Earth. It is known to be surrounded by at least four planets, including L98-59 d, a super-Earth about 58% larger than Earth, with a mass of 2.31 Earth masses. L98-59 d orbits its host every 7.45 days, at a distance of about 0.05 AU. The planet’s equilibrium temperature is estimated to be 416 K.

Since very little is known about L98-59 d’s atmosphere, a team of astronomers led by Amélie Gressierof of STScI used JWST’s Near Infrared Spectrograph (NIRSpec) to make transmission spectroscopic observations of the planet. The observations were conducted as part of Cycle 1 of JWST’s Guaranteed Time Observations (GTO) program.

“We have presented a transit observation of the super-Earth L98-59 d with the JWST NIRSpec G395H mode,” the researchers write in the paper.

By analyzing the data obtained, Gressierof’s team found evidence of the presence of sulfur species in L98-59 d’s atmosphere. In addition, hydrogen and helium appear to be background gases in the planet’s atmosphere.

According to the article, the atmosphere of L98-59 d has a high abundance of hydrogen sulfide (H₂S) and sulfur dioxide (SO₂). They ruled out the possibility that it could be caused by stellar contamination.

The astronomers note that the presence of sulfur dioxide in the atmospheres of exoplanets like L98-59 d is evidence of photochemistry. Additionally, sulfur species and clouds are generally expected to be present in the atmospheres of giant planets and brown dwarfs. They add that the ability to detect sulfur dioxide in the atmospheres of exoplanets is a crucial test for different models of planet formation.

Summarizing the results, the authors of the paper emphasize the importance of additional observations of the L98-59 d transit in order to confirm their new findings.

“If confirmed, the detection of sulfur-containing species in a hydrogen-dominated atmosphere around L98-59 d, a planet with a radius of 1.58 Earth radii, would be a significant result, as it is right at the limit for planets to have retained their primary hydrogen-helium atmospheres,” the scientists conclude.

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