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

Gressier, Amélie; Espinoza, Néstor; Allen, Natalie H.; Sing, David K.; Banerjee, Agnibha; Barstow, Joanna K.; Valenti, Jeff A.; Lewis, Nikole K.; Birkmann, Stephan M.; Challener, Ryan C.; Manjavacas, Elena; de Oliveira,, Catarina Alves; Crouzet, Nicolas and Beck, Tracy. L (2024). Hints of a Sulfur-rich Atmosphere around the 1.6 R ⊕ Super-Earth L98-59 d from JWST NIRspec G395H Transmission Spectroscopy. The Astrophysical Journal Letters, 975(1), article no. L10.

DOI: https://doi.org/10.3847/2041-8213/ad73d1

Abstract

Detecting atmospheres around planets with a radius below 1.6 R ⊕, commonly referred to as rocky planets, 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 L98-59 d (1.58 R ⊕ and 2.31 M ⊕), at the limit of rocky/gas-rich, using the JWST NIRSpec G395H mode covering the 2.8–5.1 μm wavelength range. The extracted transit spectrum from a single transit observation deviates from a flat line by 2.6σ–5.6σ, depending on the data reduction and retrieval setup. The hints of an atmospheric detection are driven by a large absorption feature between 3.3 and 4.8 μm. 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 L98-59 d 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.

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