Latitudinal distribution of hydrogen sulphide and methane in the atmospheres of Uranus and Neptune
Abstract
Observations of the near-infrared spectra (1.45-1.80 micron) of Uranus and Neptune made with the NIFS integral-field spectrometer at the Gemini/North telescope in 2009 and 2010 have been used to directly detect, for the first time, the presence of hydrogen sulphide (H2S) in the atmospheres of both the 'Ice Giants'. The observed cloud-top presence of H2S constrains the deep bulk sulphur/nitrogen abundance to exceed unity for both planets and adds to the weight of evidence that H2S ice likely forms a significant component of the main observable cloud deck. We also present an analysis of science verification observations of Neptune made in 2018 using the newly available Narrow Field Mode (NFM) of the MUSE integral-field spectrometer at the Very Large Telescope. This includes a collision-induced absorption band of hydrogen that can be used to distinguish between cloud-top height variations and variations in the methane (CH4) abundance. We find that the cloud-top mole fraction of methane decreases from roughly 5% at equatorial and mid-latitudes to values closer to 3% at polar latitudes, in rough agreement with an earlier analysis of HST/STIS Neptune observations. A similar latitudinal variation of cloud-top methane abundance for Uranus was found by HST/STIS in earlier observations, which suggests similar depletion mechanisms act in both planets' atmospheres.
- Publication:
-
EPSC-DPS Joint Meeting 2019
- Pub Date:
- September 2019
- Bibcode:
- 2019EPSC...13..430I