Aubrite meteorites: relicts of a large protoplanet Mercury? – IMPAcToR

Mercury stands out as an endmember within our solar system, characterized by its unique lithologies formed in an ultra-reducing, sulfur-rich environment. Despite being the smallest planet, Mercury intriguingly possesses the largest core in proportion. As a result, a longstanding hypothesis posits that Mercury originally had a considerably larger rocky mantle, which was largely pulverized during huge impact(s). However, due to insufficient constraints, this scenario was never confirmed and Mercury's origin continues to be a highly elusive and debated subject. Aubrites, rare achondrites with mineralogies particularly similar to that of Mercury, are known to originate from E-type asteroids, small "rubble piles" located in the innermost asteroid belt. The IMPAcToR project aims to evaluate the original hypothesis according to which aubrites are relicts of the shallow mantle of a large proto-Mercury, pulverized by one or more giant impacts, and of which a small fraction of the debris would have been implanted in the asteroid belt in the form of E-type asteroids. Supported by preliminary geochemical arguments, this hypothesis will be thoroughly tested through a multi-disciplinary approach encompassing five tasks: (1) comprehensive petrological and geochemical analysis of a unique aubrite collection, (2) in-situ Al-Mg and Mn-Cr dating of aubrites, (3) paleomagnetic study of aubrites, (4) experimental investigation of the Mercury-aubrite link, and (5) physical and numerical investigation of the impact scenario. Each of the five complementary tasks within the IMPAcToR project will offer crucial evidence either supporting or contradicting the working hypothesis. The data generated by IMPAcToR will offer unprecedented insights into Mercury's enigmatic origin, the debated genesis of aubrites, and their potential links to other terrestrial planets, particularly Earth, whose aubrites have the closest oxygen isotopic composition.