Atmospheric retrievals suggest the presence of a secondary atmosphere and possible sulfur species on L 98-59 d from JWST NIRSpec G395H transmission spectroscopy

TL;DR

This study analyzes JWST transmission spectra of exoplanet L 98-59 d, suggesting a high molecular weight atmosphere with potential sulfur compounds, indicating possible volcanic activity, and highlights the planet as a prime target for future atmospheric studies.

Contribution

First atmospheric retrievals of L 98-59 d using JWST data, indicating a high molecular weight atmosphere with sulfur species and stellar contamination effects.

Findings

Spectrum consistent with high mean molecular weight atmosphere

Possible detection of sulfur-bearing species H2S and SO2

Signs of unocculted stellar faculae

Abstract

L 98-59 d is a Super-Earth planet orbiting an M-type star. We performed retrievals on the transmission spectrum of L 98-59 d obtained using NIRSpec G395H during a single transit, from JWST Cycle 1 GTO 1224. The wavelength range of this spectrum allows us to detect the presence of several atmospheric species. We found that the spectrum is consistent with a high mean molecular weight atmosphere. The atmospheric spectrum indicates the possible presence of the sulfur-bearing species H$_2$S and SO$_2$, which could hint at active volcanism on this planet if verified by future observations. We also tested for signs of stellar contamination in the spectrum, and found signs of unocculted faculae on the star. The tentative signs of an atmosphere on L 98-59 d presented in this work from just one transit bodes well for possible molecular detections in the future, particularly as it is one of the best targets among small exoplanets for atmospheric characterization using JWST.