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Post by kosovohp on Sun Nov 14, 2010 4:14 am

Trujillo and colleagues have placed upper limits in Sedna's surface composition of 60% for methane ice and 70% for water ice.[22] The presence of methane further supports the existence of tholins on Sedna's surface, as they are produced by irradiation of methane.[24] Barucci and colleagues compared Sedna's spectrum with that of Triton and detected weak absorption bands belonging to methane and nitrogen ices. From these observations, they suggested the following model of the surface: 24% Triton-type tholins, 7% amorphous carbon, 10% nitrogen, 26% methanol and 33% methane.[25] The detection of methane and water ices was confirmed in 2006 by Spitzer Space Telescope mid-infrared photometry.[24] The presence of nitrogen on the surface suggests the possibility that, at least for a short time, Sedna may possess an atmosphere. A 200-year period exists around its perihelion during which Sedna's surface temperature may rise above the 35.6 K (−237.4C) minimum required for nitrogen to sublimate from solid to gas.[25] However, its deep red spectral slope is indicative of high concentrations of organic material on its surface, and its weak methane absorption bands indicate that methane on Sedna's surface is ancient, rather than freshly deposited. This means that Sedna is too cold for methane to evaporate from its surface and then fall back as snow, as happens on Triton and probably on Pluto.[24]



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