Confirm the H2S detection and sulfur-enrichment interpretation for HAT-P-1 b

Determine whether HAT-P-1 b truly hosts detectable hydrogen sulfide (H2S) and whether its sulfur abundance can be used as a tracer of refractory-to-volatile enrichment by obtaining observations that jointly constrain the 1.4 μm H2O band, the 3–4 μm sulfur-sensitive region, and the 4.3 μm CO2 band.

Background

The panchromatic HST and JWST transmission-spectrum retrievals provide strong evidence for H2O and CO2 but only tentative evidence for H2S. The inferred H2S feature is relatively small, is vulnerable to instrumental systematics, and is affected by degeneracies involving clouds, abundances, thermal structure, and overlapping opacities from other sulfur-bearing species such as SO2.

The authors identify coordinated observations covering the H2O, sulfur-sensitive, and CO2 spectral regions as necessary to resolve whether the H2S signal is genuine and to establish whether sulfur abundance can provide information about refractory-to-volatile enrichment pathways in giant-planet formation.

References

We caution, however, that the present \ce{H2S} inference remains tentative. Due to the relatively small feature size compared to the pronounced, broader \ce{H2O} and \ce{CO2} opacities present, the \ce{H2S} measurement is more vulnerable to instrument systematics. In addition, \ce{H2S} is photochemically coupled to other sulfur-bearing-species, especially \ce{SO2}, and overlapping opacities between these species can complicate retrieved abundance estimates \citep{Tsai2023}. Future observations that jointly constrain the 1.4~$\mu$m \ce{H$_2$O} band, the 3-4~$\mu$m sulfur-sensitive region, and the 4.3~$\mu$m \ce{CO$_2$} band will be needed to determine whether HAT-P-1 truly hosts detectable \ce{H2S} and whether its sulfur abundance can be used as a tracer of refractory-to-volatile enrichment.

— A Clearer View of HAT-P-1 b: JWST NIRSpec G395H Reveals Water, Carbon Dioxide, and Possibly Hydrogen Sulfide  (2608.28538 - Ashtari et al., 28 Aug 2026) in Section 4, Discussion, paragraph beginning “We caution, however, that the present H2S inference remains tentative.”