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Mid-infrared spectral variability for compositionally similar asteroids: Implications for asteroid particle size distributions

Vernazza, P and Carry, B and Emery, J. and Hora, J.L. and Cruikshank, D. and Binzel, R.P. and Jackson, J. and Helbert, Jörn and Maturilli, Alessandro (2010) Mid-infrared spectral variability for compositionally similar asteroids: Implications for asteroid particle size distributions. Icarus: International Journal of Solar System Studies, 207 (2). Elsevier. DOI: 10.1016/j.icarus.2010.01.011.

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Abstract

We report an unexpected variability among mid-infrared spectra (IRTF and Spitzer data) of eight S-type asteroids for which all other remote sensing interpretations (e.g. VNIR spectroscopy, albedo) yield similar compositions. Compositional fitting 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% and (2) carbonaceous chondrite and ordinary chondrite meteorites provide an equally good match to each asteroid spectrum. Following the laboratory work of Ramsey and Christensen (Ramsey, M.S., Christensen, P.R. [1998]. J. Geophys. Res. 103, 577-596), we interpret this variability to be physically caused by differences in surface particle size and/or the effect of space weathering processes. Our results suggest that the observed asteroids must be covered with very fine (<5 μm) dust that masks some major and most minor spectral features. We speculate that the compositional analysis may be improved with a spectral library containing a wide variety of well characterized spectra (e.g., olivine, orthopyroxene, feldspar, iron, etc.) obtained from very fine powders. In addition to the grain size effect, space weathering processes may contribute as well to the reduction of the spectral contrast. This can be directly tested via new laboratory irradiation experiments.

Document Type:Article
Title:Mid-infrared spectral variability for compositionally similar asteroids: Implications for asteroid particle size distributions
Authors:
AuthorsInstitution or Email of Authors
Vernazza, PESA
Carry, BObservatoire de Paris
Emery, J.Department of Earth and Planetary Sciences, Knoxville, TN 37996-1410, USA
Hora, J.L.Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
Cruikshank, D.NASA Ames Research Center, Mail Stop 245-6, Moffett Field, CA 94035, USA
Binzel, R.P.Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA 02139, USA
Jackson, J.Institute for Astrophysical Research, Boston University, Boston, MA 02215, USA
Helbert, Jörnjoern.helbert@dlr.de
Maturilli, Alessandroalessandro.maturilli@dlr.de
Date:June 2010
Journal or Publication Title:Icarus: International Journal of Solar System Studies
Refereed publication:Yes
In Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:207
DOI:10.1016/j.icarus.2010.01.011
Publisher:Elsevier
Status:Published
Keywords:Asteroiden, Spektroskopie
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Science and Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Erforschung des Weltraums
DLR - Research theme (Project):R - Vorhaben Exploration des Sonnensystems
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Terahertz and Infrared Sensors
Deposited By: Dr.rer.nat. Jörn Helbert
Deposited On:08 Nov 2011 10:28
Last Modified:20 Mar 2013 19:44

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