Global distribution of Pluto's atmosphere
Pluto's volatile atmosphere currently extends essentially uniformly around the globe and has nearly uniform thickness, discounting topographic elevation differences and tidal effects. Although in equilibrium with the surface ice, the atmosphere does not noticeably freeze out on the night side, during eclipses of the Sun by Charon, or at the poles during Pluto's present season near perihelion. The bulk thermal tide is negligible. The rotational and tidal deformations of the atmosphere affect the atmospheric thickness of 0.6--2% for a pure CH/sub 4/ atmosphere, depending on the unknown mass of Charon, and up to 15% for an atmosphere with high mean molecular weight. An important consequence of the global uniformity of Pluto's atmosphere and the observed CH/sub 4/ column abundance of 27 +- 7 m--Am is that Pluto's surface is close to 58 K over the entire globe. This compares with the value approx.43 K expected on the basis of insolation and blackbody radiation. We suggest that the explanation for Pluto's elevated surface temperature is the low thermal emissivity of solid CH/sub 4/, expected on the basis of the absence of a rotational spectrum in the gas. Solid CH/sub 4/, which covers an appreciable portion of Pluto's surface, can absorb sunlight in the visible and near-infrared bands but lacks opacity at thermal wavelengths to radiate the absorbed energy efficiently.
- Research Organization:
- McDonald Observatory and Astronomy Department, University of Texas at Austin
- OSTI ID:
- 5910480
- Journal Information:
- Astrophys. J.; (United States), Vol. 267:2
- Country of Publication:
- United States
- Language:
- English
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