Pluto's lower atmosphere structure and methane abundance from high-resolution spectroscopy and stellar occultations

E. Lellouch; B. Sicardy; C. de Bergh; H. -U. Käufl; S. Kassi; A. Campargue

doi:10.1051/0004-6361/200911633

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arXiv · 0901.4882

Pluto's lower atmosphere structure and methane abundance from high-resolution spectroscopy and stellar occultations

E. Lellouch·B. Sicardy·C. de Bergh·H. -U. Käufl·S. Kassi·A. Campargue

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Abstract

Context: Pluto possesses a thin atmosphere, primarily composed of nitrogen, in which the detection of methane has been reported. Aims: The goal is to constrain essential but so far unknown parameters of Pluto's atmosphere such as the surface pressure, lower atmosphere thermal stucture, and methane mixing ratio. Methods: We use high-resolution spectroscopic observations of gaseous methane, and a novel analysis of occultation light-curves. Results: We show that (i) Pluto's surface pressure is currently in the 6.5-24 microbar range (ii) the methane mixing ratio is 0.5+/-0.1 %, adequate to explain Pluto's inverted thermal structure and ~100 K upper atmosphere temperature (iii) a troposphere is not required by our data, but if present, it has a depth of at most 17 km, i.e. less than one pressure scale height; in this case methane is supersaturated in most of it. The atmospheric and bulk surface abundance of methane are strikingly similar, a possible consequence of the presence of a CH4-rich top surface layer.

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E. Lellouch, B. Sicardy, C. de Bergh, H. -U. Käufl, S. Kassi, A. Campargue. 2009-01-30. Pluto's lower atmosphere structure and methane abundance from high-resolution spectroscopy and stellar occultations. https://doi.org/10.1051/0004-6361%2F200911633

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