Spectroscopy in support of ExploreNEOs


OC analogs

We obtained visible and near-infrared wavelength spectra of near-Earth objects (NEOs) observed during the Warm Spitzer program ExploreNEOs. The ExploreNEOs program derived albedos and diameters of 583 objects using thermal infrared observations (Trilling et al. 2010, 2013). Our spectroscopy campaign was a complementary program that ran from Fall 2009 until Spring 2012. We have completed analysis on the near-infrared spectra taken with the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). Key conclusions from Thomas et al. (2013) are: (1) For spectra that contain near-infrared data, but lack the visible wavelength region, the Bus-DeMeo system misidentifies some S-types as Q-types. (2) We find no correlation between spectral band parameters and albedo. (3) We find negative Band Area Ratio (BAR) correlations with phase angle for Eros and Ivar, but a positive correlation for Ganymed. (4) We find evidence of spectral phase reddening for Eros, Ganymed, and Ivar. (5) We identify the likely ordinary chondrite type analogs for the appropriate objects and our resulting proporitions of H, L, and LL ordinary chondrites differ from those calculated for meteorite falls and in previous studies of ordinary chondrite-like NEOs. The figure at left shows the ordinary chondrite mineralogies for our spectral sample.

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We used the spectra to find average albedos by taxonomic class for Near-Earth Objects

Space Weathering in the Koronis Family


Space weathering is a long-standing puzzle in asteroid science that affects spectroscopic interpretations of near-Earth and Main Belt asteroids. We examined small members of the old Koronis asteroid family to investigate changes in spectral features that are evidence of space weathering. We began with a two year survey of Koronis family members using broadband photometry on the KPNO 2.1m. This survey demonstrated that the spectrophotometric slope increased as size increased. This increase of slope with respect to size (as a proxy for age, given collisional dynamics) in a population of objects with similar composition and observed at similar phase angles is interpreted to be evidence of space weathering. We followed the survey with an investigation of spectrophotometry from the Sloan Digital Sky Survey Moving Object Catalog. In addition to confirming the slope trend, we found evidence of a decrease in band depth (using i-z as a proxy for depth) with increasing size. This change of band depth is also another hallmark of space weathering.

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