Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p32b0560r&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P32B-0560
Physics
5415 Erosion And Weathering, 5464 Remote Sensing, 6055 Surfaces And Interiors, 6061 Remote Sensing, 6205 Asteroids And Meteoroids
Scientific paper
In certain regions of Eros flat deposits with surfaces perpendicular to the local gravity gradient infill bottoms of depressions. Such morphology is consistent with emplacement with no shear strength, allowing material to "pond" to an equipotential surface. However, ponded deposits currently support steep-walled grooves, impact craters, and superposed blocks, showing that subsequent to emplacement some compaction or cohesion has occurred to create non-zero shear strength. Many of the ponds are relatively blue (high 550/760 nm reflectance ratio ) and have a deeper infrared band (low 950/760 nm ratio), consistent with lesser alteration from the space environment. Such alteration by micrometeorite impacts produces relatively large aggregates of glass and crystalline material. Of 255 ponds greater than or equal to 30 m diameter mapped on the whole asteroid, 91 percent are located within 30 degrees of the equator. Zones asymmetrically around the long ends of the asteroid also have distinctively more and larger ponded deposits. Regions of pond occurrence coincide with areas having low gravity and spending a large fraction of Eros's orbital period near the terminator (due to Eros's 88 degrees obliquity). The long terminator exposure favors creation of photoelectric charge differentials between illuminated and shadowed terrain, capable of lifting and redistributing tens-of-microns size particles. We hypothesize that the ponds formed by electrostatic sedimentation processes that preferentially concentrated the finest, crystalline component of the regolith. This is consistent with the observed color properties: for mafic minerals, as grain size decreases, color becomes redder at visible wavelengths but at very fine grain sizes (less than 50 microns) this trend can be reversed and visible color becomes bluer. The extremely fine grain sizes required are consistent with the size range effectively mobilized by electrostatic levitation.
Murchie Scott L.
Robinson Mark S.
Thomas Peter C.
Veverka Joe
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