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Spectral slope variations for OSIRIS-REx target Asteroid (101955) Bennu: Possible evidence for a fine-grained regolith equatorial ridge

Authors :
Daniel J. Scheeres
Humberto Campins
Ben Rozitis
Dante S. Lauretta
Valerie B. Pietrasz
Megan Mansfield
Richard P. Binzel
Michael C. Nolan
Thomas H. Burbine
Joshua P. Emery
Beth E. Clark
Edward A. Cloutis
David Polishook
Ellen S. Howell
Brian Burt
Francesca E. DeMeo
Carl Hergenrother
Source :
Icarus. 256:22-29
Publication Year :
2015
Publisher :
Elsevier BV, 2015.

Abstract

Ongoing spectroscopic reconnaissance of the OSIRIS-REx target Asteroid (101955) Bennu was performed in July 2011 and May 2012. Near-infrared spectra taken during these apparitions display slightly more positive (“redder”) spectral slopes than most previously reported measurements. While observational systematic effects can produce such slope changes, and these effects cannot be ruled out, we entertain the hypothesis that the measurements are correct. Under this assumption, we present laboratory measurements investigating a plausible explanation that positive spectral slopes indicate a finer grain size for the most directly observed sub-Earth region on the asteroid. In all cases, the positive spectral slopes correspond to sub-Earth latitudes nearest to the equatorial ridge of Bennu. If confirmed by OSIRIS-REx in situ observations, one possible physical implication is that if the equatorial ridge is created by regolith migration during episodes of rapid rotation, that migration is most strongly dominated by finer grain material. Alternatively, after formation of the ridge (by regolith of any size distribution), larger-sized equatorial material may be more subject to loss due to centrifugal acceleration relative to finer grain material, where cohesive forces can preferentially retain the finest fraction (Rozitis, B., Maclennan, E., Emery, J.P. [2014]. Nature 512, 174–176).

Details

ISSN :
00191035
Volume :
256
Database :
OpenAIRE
Journal :
Icarus
Accession number :
edsair.doi...........9ff89288f679c229ea9067f1d8426918
Full Text :
https://doi.org/10.1016/j.icarus.2015.04.011