# # Program information file # PROGRAM_ID 2023B042 PROGRAM_TITLE Searching for andesitic asteroids to reveal the planetesimal differentiation process. PROGRAM_INV1 Marjorie Galinier PROGRAM_INV2 Chrysa Avdellidou PROGRAM_INV3 Marco Delbo PROGRAM_INV4 Laurent Galluccio PROGRAM_INV5 PROGRAM_SCICAT main-belt / Trojan asteroids PROGRAM_ABSTRACT_BEG Planetesimals that accreted early in our Solar System history are thought to have undergone differentiation, due to heating induced by the radioactive decay of 26Al. The differentiation process results in bodies organising into a metallic core, an overlaying mantle and an igneous crust classically understood to be of basaltic composition. However, the discovery of andesitic meteorites put this differentiation process into question, and the hypothesis that some planetesimals could have shown crusts of andesitic composition emerged. Erg Chech 002 [EC 002] is the oldest andesitic meteorite of the Solar System, with a crystallisation age of around 2.25 Myr after the formation of the calcium--aluminium-rich inclusions. It is understood to derive from the partial melting of a chondritic source, and its formation mechanism is consistent with a rapid cooling of a silicate-rich magma in the primitive igneous crust of an early accreted and differentiated planetesimal. Interestingly, no spectral analogue of this object has been found in the main asteroid belt to date. A recent study used Gaia Data Release 3 visible asteroid spectra and identified 51 asteroids that could potentially match the spectrum of EC 002. However the absence of the NIR wavelength range does not allow solid links. We request IRTF observing time [with Spex and MORIS] to obtain near-infrared spectra that will be combined with the Gaia DR3 spectra. We will spectroscopically characterise the visible analogues of EC 002 in the main asteroid belt, in order to assess their andesitic or basaltic composition by comparing their spectra with the laboratory spectra of EC 002. This work would allow to probe the differentiation conditions at the very early stages of the Solar System. PROGRAM_ABSTRACT_END