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Paper: Observations Constraining the Origins of Earth--Approaching Asteroids
Volume: 107, Completing the Inventory of the Solar System
Page: 13
Authors: Rabinowitz, D. L.
Abstract: Theoretical models have shown that both short-period comets and main-belt asteroids can supply the population of Earth-approaching asteroids, but the relative contribution from each source is uncertain. This paper reviews recent observations that set constraints on this problem, including new spectral observations of Earth approachers smaller than $\sim$0.05 km, reported here for the first time. For larger Earth approachers (diameters$>$$\sim$0.1 km), the debiased orbital distribution is consistent with either an asteroidal or cometary origin or both, whereas the distributions in size and spectral reflectance suggest that main-belt asteroids are the dominant source. Smaller Earth approachers (SEAs) are over-abundant relative to the size distribution of the larger Earth approachers, and their reflectance spectra are generally as red or redder than D-type asteroids. This suggests that a large fraction of the SEAs are the fragments of extinct, short-period comets. A small fraction (5 to 10\%), however, have unusually low-eccentricities, not expected from an asteroidal or cometary source, and have reflectance spectra consistent with lunar or Martian material. These low-eccentricity SEAs may be local ejecta from the Moon, Mars, Earth, or perhaps an undetected population of Earth Trojans.
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