Precursors of Mars--Constraints from nitrogen and oxygen isotopic compositions of martian meteorites

Abstract

We present an approach to assess the nature of materials involved in the accretion of Mars by the planets nitrogen (δ15N) and oxygen (∆17O) isotopic compositions as derived from data on martian meteorites. δ15N for Mars has been derived from nitrogen and xenon systematics, while ∆17O has been taken from the literature data. These signatures indicate that Mars has most probably accreted from enstatite and ordinary chondritic materials in a ratio of 74:26 and may not have a significant contribution from the carbonaceous (CI, CM, or CV) chondrites. This is consistent with the chromium isotopic (ε53Cr) signatures of martian meteorites and the bulk planet Fe/Si ratio for Mars as suggested by the moment of inertia factor (I/MR2) obtained from the Mars Pathfinder data. Further, a simple homogeneous accretion from the above two types of materials is found to be consistent with the planets moment of inertia factor and the bulk composition of the mantle. But, it requires a core with 6.7 wt% Si, which is consistent with the new results from the high pressure and temperature melting experiments and chemical data on the opaque minerals in enstatite chondrites.