Statistics
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.2502b&link_type=abstract
American Astronomical Society, DPS meeting #40, #25.02; Bulletin of the American Astronomical Society, Vol. 40, p.432
Statistics
Scientific paper
We report results from Vernazza et al. (2008; Nature, August 14 issue) showing that 2/3 of all large near-Earth objects (NEOs), including the potentially hazardous asteroid (PHA) subset, have spectral characteristics consistent with laboratory measurements of LL-chondrite meteorites. Our NEO data (38 S- and Q-types) were obtained through a joint observational program (MIT, Hawaii, IRTF). Comparison meteorite data were obtained from the Brown University RELAB database. Our asteroid-meteorite comparative analysis was performed using quantitative measurements of spectral band centers and band area ratios and using a radiative transfer model for olivine (olv) and orthopyroxene (opx) (Shkuratov 1999; Icarus 137, 235). Most large NEOs (and the PHA subset) show relatively high olv/(olv+opx) ratios in the 70-85% range typical for LL-chondrites. Interestingly, relatively high olivine abundances are found among S-type asteroids in the inner main-belt Flora region (Gaffey 1984; Icarus 60, 38: Chapman 1996; MPS 31, 699) adjacent to the nu6 secular resonance. An LL chondrite association for most large (km-sized) NEOs and PHAs is surprising since LL chondrites are somewhat rare ( 8% of all meteorite falls). One possible explanation is Yarkovsky drift. Large objects (such as km-sized NEOs in our sample) experience relatively little Yarkovsky drift. In contrast, meter-sized objects (which dominate meteorite fall statistics) experience substantial Yarkovsky drift. Limited Yarkovsky drift therefore restricts the delivery of the largest NEOs to the most favorable source region(s), such as the nu6 resonance bordering the Flora region. Substantial Yarkovsky drift of meter-sized objects throughout the main belt allows meteorite fall statistics to sample from numerous main-belt resonances. Thus, meteorite falls sample throughout_the_asteroid_belt (not just the inner belt). Such a size-dependent efficiency therefore enhances the inner main belt as the source for large NEOs and PHAs relative to a broader main belt sample for meteorite falls.
Binzel Richard P.
Bus Schelte J.
DeMeo Francesca E.
Rivkin Andrew S.
Thomas Cristina A.
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