A model for the overabundance of methane in the atmospheres of Pluto and Triton

John A. Stansberry, John R. Spencer, Bernard Schmitt, Abdel Illah Benchkoura, Roger V. Yelle, Jonathan I. Lunine

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


A model for producing atmospheric CH4 mixing ratios larger than would be expected from simple vapor pressure equilibrium over a solid solution of N2 and CH4 is described. Laboratory experiments show that rapid sublimation of a dilute (0.2% mole fraction) solid solution of CH4 in α-N2 produces a residue of nearly pure CH4 grains. The CH4 grains begin to form very quickly, and most of the CH4 originally in solid solution with the N2 is taken up by the grainy residue rather than sublimating. If the same is true for the much slower sublimation rates on Pluto, patches of nearly pure CH4 ice grains will be built up on sub-seasonal timescales. Such CH4 patches will be in contact with Pluto's predomionatly N2 atmosphere. Further sublimation of these patches wil be controlled by molecular and turbulent diffusion, as will be the condensation of CH4 from the atmosphere in other areas. It is shown that the balance between diffusive sublimation and condensation can easily produce 1% mixing ratios of CH4 in the atmosphere, generally consistent with requirements for explaining Pluto's 100K upper-atmospheric temperature and producing a steep positive temperature gradient in the 2-3 μb region. The same mechanism can explain Triton's less elevated atmospheric CH4 mixing ratio.

Original languageEnglish (US)
Pages (from-to)1051-1063
Number of pages13
JournalPlanetary and Space Science
Issue number9
StatePublished - Sep 1996
Externally publishedYes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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