(6) Hebe Really is the H Chondrite Parent Body

Details (6) Hebe Really is the H Chondrite Parent Body (6) Hebe Really is the H Chondrite Parent Body

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.4606b&link_type=abstract

American Astronomical Society, DPS meeting #42, #46.06; Bulletin of the American Astronomical Society, Vol. 42, p.1051

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In the 1990's, several authors argued that (6) Hebe, a 200 km diameter asteroid, was the source of the H chondrites (HCs). They favored it over other candidate asteroids because: (i) Hebe has the right spectroscopic signature for HCs (e.g., S (IV) class), (ii) it is located near the J3:1 mean motion and nu6 secular resonances, both key transportation routes for delivering material to Earth, and (iii) Hebe is sufficiently large that cratering events could directly inject HCs into the J3:1 and nu6 resonances. By the 2000's, though, it became increasingly clear that Yarkovsky thermal forces provide sufficient mobility to meteoroids that asteroid families far from key resonances could still dominate the delivery flux. This weakened (ii)-(iii); Hebe has no observed family, and the CRE ages for HCs peak near 7-8 Ma rather than at 1-2 Ma. New collisional, dynamical, and meteoritical work, however, allowed us to re-evaluate the situation. (a) Ar-Ar shock degassing ages are frequently produced by cratering events on large asteroids. The HCs have such ages ranging from nearly today to 4.5 Ga. If the HCs were coming from an asteroid family, few ages should exist between now and the age of the family-forming event. (b) Cratering events on Hebe should produce steep fragment distributions, thereby creating numerous meteoroids without producing an detected family. (c) The 7-8 My CRE age peak among HCs is best explained by Hebe's meteoroids being pummeled by ejecta from the 8.2 Ma Veritas family-forming event. L and LL meteoroids, thought to come from the Gefion and Flora families, respectively, are out of range of Veritas ejecta. (d) Our new meteoroid source predictor model shows of the 6 HC falls with solid orbits, 3 come from the J3:1 and 3 come from the nu6 resonance. These results are consistent with Hebe's location.

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