Reconciling near-infrared and microwave analyses of Neptune’s hydrogen sulphide distribution

Journal article

Previous analysis of Neptune’s atmosphere using near-infrared Gemini/NIFS observations found the strongest spectral signature of hydrogen sulphide (HS) to be at the planet’s south pole. Conversely, analysis of microwave observations with the Atacama Large Millimeter/submillimeter Array in 2019 suggested a distribution of HS that peaks in the mid-latitudes and is strongly depleted towards the pole. We analyse near-infrared observations from VLT-SINFONI in 2018 and fit a parametrized cloud model to the data using nested sampling. By prescribing a latitudinally varying methane (CH) profile previously derived from visible light observations, we find general agreement with the microwave analysis, with an enhancement of HS by a factor of 4 at the southern mid-latitudes compared to polar latitudes. The stronger spectral signature at the pole is explained with a deeper cloud top, resulting in a higher cloud-top HS column abundance in this region. Our results are indicative of deep upwelling at the mid-latitudes, with downwelling at the pole and possibly near the equator.

Authors: Penn, J; Irwin, PGJ; Dobinson, J; Fletcher, LN; Teanby, NA

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 548
• Issue: 2
• Pages: stag688
• Article number: stag688
• Publication date: 2026-04-14
• Acceptance date: 2026-04-07
• DOI: 10.1093/mnras/stag688
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: planets and satellites: atmospheres; scattering; techniques: imaging spectroscopy; radiative transfer