Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.0107s&link_type=abstract
American Astronomical Society, DPS meeting #42, #1.07; Bulletin of the American Astronomical Society, Vol. 42, p.942
Astronomy and Astrophysics
Astronomy
Scientific paper
Images of thermal emission from Mimas taken at a wavelength of 9 - 16 µm by Cassini's Composite Infrared Spectrometer (CIRS) in February 2010, centered near longitude 150 W, reveal an extremely unusual pattern of daytime temperatures. Low- and mid-latitudes on the leading hemisphere are up to 15 K colder than both the visible portions of the trailing hemisphere, and high latitudes on the leading hemisphere. The same pattern is also evident, with benefit of hindsight, in lower-resolution CIRS Mimas data taken in 1995. The V-shaped boundary between the warmer and colder regions is sharp at CIRS resolution ( 15 km), and does not correspond to any dramatic change in surface albedo in clear-filter ISS images, suggesting that thermal inertia variations are probably largely responsible for the anomaly: the cold region appears to have unusually high thermal inertia. Global color maps of Mimas (Schenk et al. 2010, Plasma, plumes and rings: Saturn system dynamics as recorded in global color patterns on its midsize icy satellites, Icarus, in press), show an unusually blue region centered on Mimas' apex of orbital motion, that is similar in shape and extent, and thus may have the same cause, as the observed portion of the cold region seen by CIRS. Schenk et al. note that the shape of the blue region is consistent with its formation by irradiation of Mimas' surface by high-energy electrons, and it is therefore possible that the CIRS thermal anomaly has the same cause. However the mechanism by which electron irradiation could produce the high thermal inertias necessary to explain the observed temperatures in the cold region is still mysterious.
Howett C. J.
Hurford Terry A.
Pearl John C.
Schenk Paul
Segura Marcia E.
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