Detection of a CH4 atmosphere on Pluto

Uwe Fink, Bradford A. Smith, D. Chris Benner, James R. Johnson, H. J. Reitsema, James A. Westphal

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


Using a low-resolution spectrograph and a CCD array, a spectrum of Pluto from 0.58 to 1.06 μm was obtained. The spectrum had a resolution of ∼25 Å and a signal-to-noise ratio of ∼300. It showed CH4 absorption bands at 6200, 7200, 7900, 8400, 8600, 8900 and 10,000 Å. The strongest of these bands was at 8900 Å with an absorption depth of 0.23. This band was heavily saturated, compared to the weaker bands, providing proof for the gaseous origin of the observed absorptions. By applying CH4 band model parameters to our data, a total CH4 abundance of 80 ± 20 m-am was derived. This translates into a one-way abundance of 27 ± 7 m-am and a CH4 surface pressure of 1.5 × 10−4 atm. An upper limit to the total pressure of ∼0.05 atm could be set. First-order calculations on atmospheric escape showed that this methane atmosphere would be stable if the mass of Pluto is increased 50% over its current value and its radius is 1400 km. Alternatively a heavier gas mixed with the CH4 atmosphere would aid its stability. The relatively large amount of gaseous CH4 observed implies that the absorption bands recently reported at 1.7 and 2.3 μm are likely due to atmospheric CH4 absorptions rather than surface frost as interpreted earlier.

Original languageEnglish (US)
Pages (from-to)62-71
Number of pages10
Issue number1
StatePublished - Jan 1 1980

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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