* Astronomy

Title: Near-Earth Asteroid Origin for the Farmington Meteorite
Authors: Marti, K., Mathew, K. J.

Although the asteroid belt is considered the ultimate source of ordinary chondrites, extremely short CRE ages of chondrites are difficult to reconcile with delivery considerations from this source. It had been noted that shocked L-chondrites with low 40Ar (<10-5 cm^3 STP/g) concentrations and very low 4He tend to have lower exposure ages and that none of these contain solar-type gases. The Farmington (L5) chondrite is known for its extremely short CRE age of 25-30 Ka. The orbit of the Farmington parent was reconstructed by Levin et al.  as a small orbit of low inclination with perihelion =>0.4 AU. These authors conclude that the extremely short CRE age implies that the parent object must have been in an Earthcrossing orbit. The records of radiogenic gases in Farmington show that its parent body was severely degassed in a recent collisional event ~500 Ma ago. We investigate the nitrogen isotopic signatures for evidence of collisional perturbances, as two distinct nitrogen signatures in metal phases of the Portales Valley chondrite suggested their use as tracers for possible impactors. The short CRE age of the Farmington meteorites does not require consideration of spallation 15Nc.

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