Compositional homogeneity of CM parent bodies.

Abstract

CM chondrites are the most common type of hydrated meteorites, making up ∼1.5% of all falls. Whereas most CM chondrites experienced only low-temperature (∼0°C–120°C) aqueous alteration, the existence of a small fraction of CM chondrites that suffered both hydration and heating complicates our understanding of the early thermal evolution of the CM parent body(ies). Here, we provide new constraints on the collisional and thermal history of CM-like bodies from a comparison between newly acquired spectral measurements of main-belt Ch/Cgh-type asteroids (70 objects) and existing laboratory spectral measurements of CM chondrites. It first appears that the spectral variation observed among CM-like bodies is essentially due to variations in the average regolith grain size. Second, the spectral properties of the vast majority (unheated) of CM chondrites resemble both the surfaces and the interiors of CM-like bodies, implying a “low” temperature ( 100 km)—supposedly primordial—Ch/ Cgh-type main-belt asteroids likely expose the interiors of the primordial CM parent bodies, a possible consequence of impacts by small asteroids (D < 10 km) in the early solar system.The MIT component of this work is supported by NASA grant 09-NEOO009-0001, and by the National Science Foundation under grants Nos. 0506716 and 0907766. F.E.D. acknowledges support from NASA under grant No. NNX12AL26G issued through the Planetary Astronomy Program. E.A.C. thanks the Canada Foundation for Innovation, the Manitoba Research Innovations Fund, the Canadian Space Agency, the University of Winnipeg, and the Natural Sciences and Engineering Research Council of Canada for supporting the establishment and operation of the University of Winnipeg's Planetary Spectrophotometer Facility and this study.http://iopscience.iop.org/article/10.3847/0004-6256/152/3/54/met