A Model for the Self-Heating of Asteroid Surfaces: Application to the Interpretation of Combined MIRO-VIRTIS Data During the Rosetta Fly-by of 21 Lutetia

Details A Model for the Self-Heating of Asteroid Surfaces: Application to the Interpretation of Combined MIRO-VIRTIS Data During the Rosetta Fly-by of 21 Lutetia A Model for the Self-Heating of Asteroid Surfaces: Application to the Interpretation of Combined MIRO-VIRTIS Data During the Rosetta Fly-by of 21 Lutetia

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p23c1722k&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P23C-1722

Physics

Geophysics

[0933] Exploration Geophysics / Remote Sensing, [6205] Planetary Sciences: Solar System Objects / Asteroids

Scientific paper

During the July 10, 2010 flyby of Asteroid 21 Lutetia by the Rosetta spacecraft, maps of surface and subsurface temperatures were derived from the VIRTIS and MIRO instruments respectively. Both data sets indicated a porous surface layer with an extremely low, lunar-like thermal inertia. However, comparisons of the VIRTIS-measured and MIRO-modelled surface temperatures revealed offsets of 10- 30 K, indicative of self-heating or "beaming" effects - commonly attributed to negative relief features - that were not taken into account in the MIRO thermal modeling. The customary approach to modeling the self-heating effect is inclusion of a "beaming" parameter in the radiative balance equation of the surface. The net effect is a decrease in the "effective" emissivity of the surface and subsequent increase in the surface flux relative to a smooth surface in radiative equilibrium with the solar insolation. One deficiency of the "beaming parameter" approach is the dependency on wavelength of observation. Near-IR and mid-IR measurements of surface temperature can differ due to different levels of non-linearity in the Planck relation between flux and temperature. A second deficiency appears when the objects of interest are well resolved: beaming parameters required to fit the surface temperature measurements can vary with observational phase angle. To account for the offsets in VIRTIS-measured and MIRO modeled surface temperatures, a physical model approach has been adopted in which dayside temperature distributions on the floors of spherical-shaped craters are computed as a function of incident sun angle and the subsequent flux enhancements evaluated as a function of observing angle. The results indicate that a model of hemispherical craters at all scales 1 cm and larger, covering %50 of the surface, removes most of the offsets in the VIRTIS, MIRO surface temperature determinations, including correctly predicting the limb brightening observed by VIRTIS. Similar modeling results for other airless planetary bodies with low thermal inertia surfaces suggest that the crater model of self-heating may be applicable for a large class of asteroids and comet nuclei.

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