Mid-infrared Spectral Variability For Compositionally Similar Asteroids

Details Mid-infrared Spectral Variability For Compositionally Similar Asteroids Mid-infrared Spectral Variability For Compositionally Similar Asteroids

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.5309v&link_type=abstract

American Astronomical Society, DPS meeting #41, #53.09

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Scientific paper

We report an unexpected variability among mid-infrared spectra (IRTF and Spitzer data) of 8 S-type asteroids for which all other remote sensing interpretations (e.g. VNIR spectroscopy, albedo) yield similar compositions. Compositional modelling making use of their mid-IR spectra only yields surprising alternative conclusions: 1) these objects are not "compositionally similar” as the inferred abundances of their main surface minerals (olivine and pyroxene) differ from one another by 35%. 2) Carbonaceous chondrite and ordinary chondrite meteorites provide an equally good match to each asteroid spectrum.
Following the laboratory work of Ramsey & Christensen (1998), we interpret this variability to be physically caused by differences in surface particle size. Mid-IR measurements of surfaces having particle sizes that are large compared to the 8-13 µm wavelength range yield compositional interpretations that remain compatible with other types of remote sensing. Surfaces having grain sizes near or below the 8-13 µm wavelength scale of mid-IR measurements yield divergent compositional interpretations. Thus for asteroids, we find mid-infrared measurements are a powerful tool for inter-comparison of surface properties for objects of known compositions. Those yielding compatible mid-IR compositional interpretations likely have large particle sizes on their surfaces. Divergent compositional interpretations are more likely indicative of surfaces dominated by particles at or below the 8-13 µm scale of mid-IR radiation. Thus for mid-IR measurements of objects whose surface properties are not known, a reliable compositional interpretation based solely on
linear deconvolution of mid-IR measurements with existing spectral libraries is problematic.

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