Hints of a Sulfur-rich Atmosphere around the 1.6 R ⊕ Super-Earth L98-59 d from JWST NIRspec G395H Transmission Spectroscopy

Detecting atmospheres around planets with a radius below 1. 6 R_, commonly referred to as rocky planets (Rogers₂015, Rogers₂021), has proven to be challenging. However, rocky planets orbiting M-dwarfs are ideal candidates due to their favorable planet-to-star radius ratio. Here, we present one transit observation of the Super-Earth L98-59d (1. 58 R_, 2. 31 M_), at the limit of rocky/gas-rich, using the JWST NIRSpec G395H mode covering the 2. 8 to 5. 1 microns wavelength range. The extracted transit spectrum from a single transit observation deviates from a flat line by 2. 6 to 5. 6, depending on the data reduction and retrieval setup. The hints of an atmospheric detection are driven by a large absorption feature between 3. 3 to 4. 8 microns. A stellar contamination retrieval analysis rejected the source of this feature as being due to stellar inhomogeneities, making the best fit an atmospheric model including sulfur-bearing species, suggesting that the atmosphere of L98-59d may not be at equilibrium. This result will need to be confirmed by the analysis of the second NIRSpec G395H visit in addition to the NIRISS SOSS transit observation.