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- Title
Latitudinal variation in abundance of hydrogen sulphide (H2S) and methane (CH4) in the atmosphere of Neptune.
- Authors
Irwin, Patrick G. J.; Fletcher, Leigh N.; Teanby, Nicholas A.; Orton, Glenn S.; Toledo, Daniel; Braude, Ashwin; Bezard, Bruno
- Abstract
Observations of the visible and near-infrared spectra of Neptune have been made recentlywith two integral-field spectrometers: the MUSE instrument at ESO’s Very Large Telescope,and the NIFS instrument at the Gemini/North telescope. These observations image the entireobservable disc of Neptune at sub-arcsecond resolution with each 'pixel’ containing acomplete spectrum from either 480 – 930 nm (MUSE) or 1.45 – 1.80 μm (NIFS).The VLT/MUSE spectral range includes a collision-induced absorption band ofhydrogen near 825 nm and the observed spectra can be used to disentangle cloud-topheight variations from variations in methane (CH4) abundance. We find that thecloud-top abundance of methane mole fraction decreases from ∼ 4% at equatorialand mid latitudes to values closer to 2% at polar latitudes, in agreement with anearlier analysis HST/STIS observations [Karkoschka and Tomasko, 2011]. At longerwavelengths, the Gemini/NIFS spectral range includes a weak absorption bandof hydrogen sulphide (H2S) and from these observations we directly detect, forthe first time, the presence of this gas in Neptune’s atmosphere. We find that thecloud-top abundance (at 2.5 – 3.5 bar) of H2S is 1–3 ppm, with a clearer detection nearNeptune’s south pole. The observed cloud-top presence of H2S constrains the deep bulksulphur/nitrogen abundance to exceed unity and adds to the weight of evidence that H2S icelikely forms a significant component of the main observable cloud deck. We havealso analysed both sets of data using a Principal Component Analysis (PCA) andwe will discuss what these observations reveal about the vertical and latitudinaldistribution of cloud, hydrogen sulphide and methane in Neptune’s atmosphere.
- Subjects
EUROPEAN Southern Observatory; HYDROGEN sulfide; METHANE; PRINCIPAL components analysis; VISIBLE spectra; MOLE fraction
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article