NWA 12774 Angrite Records 17.5 kbar Pressures Indicating 1800 km Protoplanet Destroyed 4.56 Ga

{"Northwest Africa 12774 was examined by Bell’s group at Colorado Boulder using electron microprobe and thermodynamic modeling of aluminum partitioning in clinopyroxene. The mineral assemblage records crystallization pressures far above those possible in any asteroid smaller than 1000 km. Preservation of sharp crystal edges further constrains formation to shallow depths within a body whose total radius approached lunar scale, overturning prior models that limited angrite sources to <200 km objects.","This size estimate reframes angrites as fragments of a differentiated protoplanet whose mantle composition diverged sharply from Earth and Mars in silica and volatile budgets. Such divergence implies the body accreted from a distinct reservoir, possibly interior to the snow line, and was destroyed before it could deliver its inventory to the terrestrial planets. The chemistry therefore supplies a concrete mechanism for heterogeneous volatile delivery that current origin-of-life models have not yet incorporated.","Existing angrite collections contain dozens of unanalyzed specimens; systematic high-pressure mineral surveys of these samples could identify additional large parent bodies. Within five years, combined isotopic and trace-element datasets from such finds will test whether multiple Moon-sized embryos were lost during the giant-impact phase, tightening constraints on the dynamical excitation required to match the current terrestrial planet masses."}