Hydrogen Sulfide and Metal-Enriched Atmosphere for a Jupiter-mass Exoplanet

As the closest transiting hot Jupiter to Earth, HD 189733b has been the benchmark planet for atmospheric characterization(1-3). It has also been the anchor point for much of our theoretical understanding of exoplanet atmospheres from composition(4), chemistry(5,6), aerosols(7) to atmospheric dynamics(8), escape(9) and modelling techniques(10,11). Previous studies of HD 189733b have detected carbon and oxygen-bearing molecules H2O and CO (refs. 12,13) in the atmosphere. The presence of CO2 and CH4 has been claimed(14,15) but later disputed(12,16,17). The inferred metallicity based on these measurements, a key parameter in tracing planet formation locations(18), varies from depletion(19,20) to enhancement(21,22), 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 (2.4-5.0 mu m) of HD 189733b. With an equilibrium temperature of about 1,200 K, H2O, CO and H2S are the main reservoirs for oxygen, carbon and sulfur. Based on the measured abundances of these three main volatile elements, we infer an atmospheric metallicity of three to five 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 pathway23.