astro-ph.EP

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

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.
 Comments: AA vers. 6.1, LaTeX class for Astronomy & Astrophysics, 9 pages with 5 figures Astronomy and Astrophysics Letters, in press Subjects: Earth and Planetary Astrophysics (astro-ph.EP) DOI: 10.1051/0004-6361/200911633 Cite as: arXiv:0901.4882 [astro-ph.EP] (or arXiv:0901.4882v1 [astro-ph.EP] for this version)

## Submission history

From: Emmanuel Lellouch [view email]
[v1] Fri, 30 Jan 2009 13:43:50 GMT (128kb)
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