12:00 PM - 1:00 PM
Anomalies involving heavy isotopes of Cr, Ti, and to a lesser extent (given limitations of current data sets) Ni and Ca, in conjunction with oxygen isotopes, reveal a strong binary clustering among planetary materials. The top-level classification of planetary materials ought to be revised accordingly, into a dichotomy between carbonaceous and noncarbonaceous materials. The binary clustering may be reconciled with traditional Solar System origin models by assuming grossly heterogeneous accretion within the protoplanetary disk, but in my view it more likely reflects an early-accretion-location dichotomy, between the outer solar system (carbonaceous, C) and the inner solar system (noncarbonaceous, NC). Proportions of C/(C+NC) materials are: <18% in Mars, <32% in Earth.