Differentiated Planetesimals and the Parent Bodies of Chondrites

Abstract

Meteorites are samples of dozens of small planetary bodies that formed in the early Solar System. They exhibit great petrologic diversity, ranging from primordial accretional aggregates (chondrites), to partially melted residues (primitive achondrites), to once fully molten magmas (achondrites). It has long been thought that no single parent body could be the source of more than one of these three meteorite lithologies. This view is now being challenged by a variety of new measurements and theoretical models, including the discovery of primitive achondrites, paleomagnetic analyses of chondrites, thermal modeling of planetesimals, the discoveries of new metamorphosed chondrites and achondrites with affinities to some chondrite groups, and the possible identification of extant partially differentiated asteroids. These developments collectively suggest that some chondrites could in fact be samples of the outer, unmelted crusts of otherwise differentiated planetesimals with silicate mantles and metallic cores. This may have major implications for the origin of meteorite groups, the meaning of meteorite paleomagnetism, the rates and onset times of accretion, and the interior structures and histories of asteroids.

Hydrothermal preparation of analogous matrix minerals of CM carbonaceous chondrites from metal alloy particles

“…A direct deduction of the above alteration scheme is that the parent asteroids of CM chondrites may have a multiple-layered structure, similar to the structures suggested by Weiss and coworkers (Carporzen et al, 2011;Elkins-Tanton et al, 2011;Weiss and Elkins-Tanton, 2013).…”

Chondrules: Ubiquitous Chondritic Solids Tracking the Evolution of the Solar Protoplanetary Disk

“…Thus, protracted asteroidal accretion predicts the existence of partially differentiated asteroidal bodies, namely onion-shell structured bodies with differentiated interiors consisting of silicate mantles and metallic cores surrounded by unmelted chondritic crusts (Weiss and Elkins-Tanton 2013). Although controversial, this proposal is apparently supported by the discovery of remnant magnetism in chondritic meteorites suggesting the existence of dynamo field (Carporzen et al 2011), which can only occur through the establishment of a convecting metallic core.…”

Major element composition of an Early Enriched Reservoir: constraints from 142Nd/144Nd isotope systematics in the early Earth and high-pressure melting experiments of a primitive peridotite

“…At present, the bulk compositions of the Moon and Mars remain imprecisely determined. Moreover, the fractionation between Sm and Nd associated with silicate differentiation during planetesimal collisions is also an unknown factor (Weiss and Elkins-Tanton 2013).…”