Hydrogen sulfide and metal-enriched atmosphere for a Jupiter-mass exoplanet

TL;DR

This study detects key molecules in the atmosphere of the hot Jupiter HD 189733b, revealing a metallicity 3-5 times stellar and supporting formation via water-rich icy planetesimals.

Contribution

It provides the first robust detections of H2O, CO2, CO, and H2S in HD 189733b's atmosphere, refining understanding of its composition and formation history.

Findings

Detected H2O, CO2, CO, and H2S with high significance.

Inferred atmospheric metallicity of 3-5 times stellar.

Low methane abundance suggests formation through icy planetesimals.

Abstract

As the closest transiting hot Jupiter to Earth, HD 189733b has been the benchmark planet for atmospheric characterization. It has also been the anchor point for much of our theoretical understanding of exoplanet atmospheres from composition, chemistry, aerosols to atmospheric dynamics, escape, and modeling techniques. Prior studies of HD 189733b have detected carbon and oxygen-bearing molecules H2O and CO in the atmosphere. The presence of CO2 and CH4 has been claimed but later disputed. The inferred metallicity based on these measurements, a key parameter in tracing planet formation locations, varies from depletion to enhancement, hindered by limited wavelength coverage and precision of the observations. Here we report detections of H2O (13.4 sigma), CO2 (11.2 sigma), CO (5 sigma), and H2S (4.5 sigma) in the transmission spectrum (2.4-5 micron) of HD 189733b. With an equilibrium temperature of ~1200K, H2O, CO, and H2S are the main reservoirs for oxygen, carbon, and sulfur. Based on the measured abundances of these three major volatile elements, we infer an atmospheric metallicity of 3-5 times stellar. The upper limit on the methane abundance at 5 sigma is 0.1 ppm which indicates a low carbon-to-oxygen ratio (<0.2), suggesting formation through the accretion of water-rich icy planetesimals. The low oxygen-to-sulfur and carbon-to-sulfur ratios also support the planetesimal accretion formation pathway.