Researchers, including academics from The Open University (OU) have discovered a possible sulphur-rich atmosphere of exoplanet L 98-59 d, signalling possible volcanoes on its surface.
The study, which has been undertaken using observations from NASA’s James Webb Telescope (JWST) has been published in two papers in The Astrophysical Journal.
Experts observed one transit of the exoplanet across its host star (L 98-59, an M-dwarf star ~35 light years away) using the NIRSpec G395H instrument on JWST, as part of the GTO program 1224. They then obtained the transmission spectrum of the atmosphere of the exoplanet from these observations.
Agnibha Banerjee, Research Student at the OU and lead author of one of the papers, said:
“We have discovered tentative signs of a sulphur-rich atmosphere on the exoplanet L 98-59 d. If these findings can be confirmed with future observations, it could hint at the presence of volcanoes on the planet’s surface.”
This spectrum suggested the possible presence of an atmosphere filled with Sulphur dioxide (SO2) and Hydrogen sulphide (H2S). Atmospheric retrievals were then performed on the dataset, a technique used to infer the atmospheric properties of a planet from its measured spectrum, to establish statistical bounds on the possible abundances of these gases.
However, given the single transit, the data did not provide strong constraints, and additional observations will be necessary to confirm the presence of these gases.
Dr Joanna Barstow, OU Research Fellow and co-author of the research, said
“Seeing hints of an atmosphere on a rocky exoplanet is really exciting, and is an important step towards learning about the diversity of rocky worlds outside our own solar system.”
L 98-59 d is a very interesting planet, slightly bigger and heavier than the Earth, the likes of which do not exist in our Solar system. The potential presence of SO2 and H2S is particularly intriguing, as it raises questions about their origin. One possibility is volcanism driven by tidal heating, much like what is observed on Jupiter’s moon Io.
If future observations support the presence of such an atmosphere, not only would it be smallest exoplanet to have a detected atmosphere, but also a crucial step towards understanding the nature of such planets.
Amélie Gressier, post-doctoral fellow at Space Telescope Science Institute in Baltimore, US and lead author of one of the research papers, added:
“L 98-59 d, with its 1.6 Earth radius, falls in the radius valley—a region where rocky planets transition to gas-rich ones. Detecting an atmospheric signal here is challenging, but JWST is the only telescope capable of capturing these subtle hints of molecular features. It’s exciting to begin exploring atmospheres on planets this small, and while further confirmation is needed, JWST is working wonderfully!”
Read both papers online:
