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If Primitive Meteorites are not Representative Samples of Asteroids then What Are They?

Published onJun 01, 2020
If Primitive Meteorites are not Representative Samples of Asteroids then What Are They?

It has become increasingly clear from ground based studies and space missions that the primary components of rubble pile asteroids are not representative of meteorites in our museum collections. In particular, it appears that meteorites have higher density, lower porosity and greater tensile strength than asteroidal material of the associated spectral class. The best studied example of a near-Earth asteroid is now Ryugu and well observed characteristics of its components do not match those of any known meteorite class. We propose that the observed differences arise because meteorites have, in general, undergone one or more episodes of lithification not widely experienced by primitive asteroidal material. Properties of this brief, intense heating event (or events) are recorded in their chondrules, and those events have served to increase the tensile strength of meteorites to the point that, unlike most primitive asteroidal material, they are able to survive passage through the Earth’s atmosphere. We predict that chondrules are a by-product of these heating events and, as such, will not be as common on asteroids as they are in meteorites. A plausible model of the heating events, which satisfies many severe constraints imposed by chondrule properties, is the flyby model, in which a small, primitive planetesimal is exposed to radiation from lava at the surface of a larger, differentiated body, during a close orbit or accretion event.

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