Probing Thermal Properties of Vesta's Surface Materials

Details Probing Thermal Properties of Vesta's Surface Materials Probing Thermal Properties of Vesta's Surface Materials

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.2203v&link_type=abstract

American Astronomical Society, DPS meeting #40, #22.03; Bulletin of the American Astronomical Society, Vol. 40, p.425

Astronomy and Astrophysics

Astronomy

Scientific paper

Observations providing longitudinal coverage across Vesta's surface with a sub-Earth latitude of -20° were obtained using the 6.5-m MMT telescope on UT 28, 30 April and 1 May, 2007. The observations were taken using the MMT f/15 natural guide star AO system coupled with a photometer cycled periodically between L' (3.8 µm) and M' (4.7µm) filters designed to avoid the telluric water present in this spectral region. The mean Earth - Vesta distance ranged from 1.27 - 1.26 AU. We examined the data in both disk integrated and disk resolved forms at 6° longitudinal bins. Preliminary photometry of the whole disk created by summing and normalizing the images shows variation in the L' photometry consistent with the variation observed at shorter wavelengths, and is consistent with the variations in reflectance spectroscopy seen in previous investigations. In contrast, the M' photometry is brighter, and has a lower amplitude lightcurve.
Maximum entropy deconvolution shows surface features in the L' images consistent with those seen at VNIR wavelengths. These features are absent from the M' deconvolved images. Calculations of the reflectance and thermal contributions from Vesta at each wavelength show that the reflected light dominates the L' photometry (72 %). The M’ photometry is dominated by the Wien-side thermal emission from Vesta's surface at that wavelength (82 %). The exponential sensitivity of this emission to temperature allows us to test for the effects of thermal inertia and compare radiometrically determined variations in local albedo with those determine solely by reflectance measurements. Thus, these observations, spanning the transition region between reflected light and thermal emitted radiation, can be used to extend our knowledge of the manifestation of variations in Vesta's surface composition into the near-infrared, and explore whether physical properties impacting thermal emission vary across the surface spectral units of the asteroid.

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