The Onset of Differentiation and Internal Evolution: the case of 21 Lutetia

TL;DR

This study uses numerical modeling to investigate Lutetia's internal evolution, suggesting it underwent partial differentiation primarily driven by Al26 heat, with core formation occurring within a few million years.

Contribution

The paper introduces a new numerical code to simulate Lutetia's geophysical history, focusing on the effects of radiogenic heating and porosity on differentiation.

Findings

Al26 is the main heat source for differentiation.

Partial differentiation occurs if accretion is within 0.7 Ma of Al26 injection.

Proto-core formation takes 1-4 Ma, with core sizes from 6 to 30 km.

Abstract

Asteroid 21 Lutetia, visited by the Rosetta spacecraft, plays a crucial role in the reconstruction of primordial phases of planetary objects. Its high bulk density and its primitive chondritic crust (Weiss et al. 2011) suggest that Lutetia could be partially differentiated. We developed a numerical code, also used for studying the geophysical history of Vesta (Formisano et al., submitted), to explore several scenarios of internal evolution of Lutetia, differing in the strength of radiogenic sources and in the global post-sintering porosity. The only significant heat source for partial differentiation is represented by Al26, the other possible sources (Fe60, accretion and differentiation) being negligible. In scenarios in which Lutetia completed its accretion in less than 0.7 Ma from injection of Al26 in Solar Nebula and for post-sintering values of macroporosity not exceeding 30 vol. %, the asteroid experienced only partial differentiation. The formation of the proto-core, a structure enriched in metals and also containing pristine silicates, requires from 1 to 4 Ma: the size of the proto-core varies from 6 to 30 km.