Chondrites as Samples of Differentiated Planetesimals

Details Chondrites as Samples of Differentiated Planetesimals Chondrites as Samples of Differentiated Planetesimals

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.0204e&link_type=abstract

American Astronomical Society, DPS meeting #42, #2.04; Bulletin of the American Astronomical Society, Vol. 42, p.944

Astronomy and Astrophysics

Astronomy

1

Scientific paper

Chondritic meteorites are unmelted, variably metamorphosed samples of the earliest solids of the solar system. The variety of metamorphic textures in ordinary chondrites motivated the "onion shell” model in which chondrites originated at varying depths within a parent body heated primarily by the short-lived radioisotope 26Al, with the highest metamorphic grade originating nearest the center (Jeffrey Taylor et al. 1987). Allende and a few other chondrites possess a unidirectional magnetization (Butler 1972, Weiss et al. 2010) that can be best explained by a core dynamo on their parent body (Funaki and Wasilewski 1999, Weiss et al. 2010), indicating internal melting and differentiation. Here we show that a parent body that accreted to > 200 km in radius by 1.7 Ma after the formation of calcium-aluminium inclusions (CAIs) could retain a solid undifferentiated crust overlying a differentiated interior, and would be consistent with formational and evolutionary constraints on the CV parent body. This body could have produced a magnetic field lasting more than 10 Ma. This hypothesis modifies the image of some chondrites as the least processed of early solar system materials, and presents them instead as the unprocessed crusts of internally melted early planetesimals. Further, the shapes and masses of the two largest asteroids, 1 Ceres and 2 Pallas, are consistent with differentiated interiors, conceivably with small iron cores with hydrated silicate or ice-silicate mantles. This research is funded by an NSF Astronomy CAREER award and a NASA/Dawn co-investigator grant.

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