Masters of disguise: can achondrite parent bodies hide beneath a chondritic cover?

Chondrite meteorites are the most primitive known building blocks of terrestrial planets
as they show elemental abundances as still found in our Sun [1]. Other groups of meteorites known
as achondrites and iron meteorites show various degrees of differentiation resembling the Earth's
basaltic crust and iron core, respectively. Traditionally, these categories of meteorites have been
interpreted to derive from more primitive (chondrites) and more differentiated (achondrites, and irons)
parent bodies, respectively. However, an alternative interpretation has it that even differentiated
parent bodies can retain an undifferentiated chondritic crust [2]. This theory is consistent with
observation of asteroid 21 Lutetia that has a chondritic surface composition but appears to be
internally differentiated [3]. That scenario could arise in small planetesimals that experience internal
heating from short-lived radionuclide decay. Partial melting and internal magmatism would facilitate
differentiation of the interior while an outer crust remains intact and unprocessed. However, that
regime will likely be restricted to a certain size and formation age of parent bodies. In earlier or larger
planetesimals, more intense heating and internal dynamics might lead to tectonic disruption and/or
volcanic resurfacing of the chondritic lid. A new generation of multi-phase reaction-transport models
for magma transport through deforming ductile-brittle rock [4-6] will allow us to put the hypothetical
stability of a chondritic crust on an achondrite parent body to the test!