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| CM carbonaceous chondrite | |
|---|---|
| Name | CM carbonaceous chondrite |
| Type | Carbonaceous chondrite |
| Class | CM |
| Country | Various |
| Region | Various |
| Fall find | Falls and finds |
CM carbonaceous chondrite is a group of primitive meteorites classified within the carbonaceous chondrites that preserve early Solar System materials and aqueous alteration signatures. These meteorites inform studies of Solar System formation, planetary accretion, and prebiotic chemistry through their preserved minerals, isotopic anomalies, and organic inventories. CM specimens are central to comparisons with samples returned by missions such as OSIRIS-REx, Hayabusa2, and investigations tied to NASA and JAXA exploration programs.
CM chondrites are defined as a petrologic subset within the carbonaceous chondrite clan, historically linked to the prototype meteorite Mighei and the type sample Murchison; classification criteria were developed by researchers at institutions including Smithsonian Institution, Natural History Museum, London, and Lunar and Planetary Institute. They are grouped alongside CI, CO, CV, CR, and CH classes in classification schemes refined by the Meteoritical Society and cataloged in the Meteoritical Bulletin. CM chondrites are often described by petrologic type (e.g., 1–3) denoting degrees of thermal metamorphism and aqueous alteration, an approach formalized in studies by teams at NASA Goddard Space Flight Center and the University of Chicago.
CM samples contain abundant matrix dominated by fine-grained phyllosilicates such as serpentine and cronstedtite, along with Fe–Ni metal, sulfides (notably pyrrhotite), magnetite, and calcium–aluminum–rich inclusions containing forsterite and enstatite; these mineral phases have been analyzed by laboratories at California Institute of Technology, Massachusetts Institute of Technology, and Max Planck Institute for Chemistry. Accessory phases include carbonates, tochilinite, and tochilinite–cronstedtite intergrowths identified in studies by groups at University of Tokyo and ETH Zurich. Bulk elemental compositions display elevated volatile and lithophile element abundances relative to ordinary chondrites, a signature investigated by researchers affiliated with Carnegie Institution for Science and Brown University.
Petrographic investigations reveal fine-grained chondrules set in a highly porous matrix; alteration textures record pervasive aqueous alteration on the parent body driven by heat sources examined by scholars at Stanford University and Caltech. Replacement of anhydrous silicates by phyllosilicates, formation of carbonates, and redistribution of sulfur phases document fluid–rock interactions analogous to hydrothermal systems studied by teams from University of Manchester and University of Oxford. Degrees of alteration vary among CM specimens, producing a sequence used by the Vernadsky Institute and the University of New Mexico to infer parent body thermal histories and impact processing recorded in breccias and fusion crusts.
CM chondrites are renowned for enriched isotopic signatures in hydrogen, nitrogen, and oxygen reservoirs, with anomalous D/H and 15N/14N ratios mapped by facilities at The Open University, Massachusetts Institute of Technology, and University of California, Los Angeles. These isotopic features link CM materials to cometary and interplanetary dust populations studied by European Space Agency missions and investigators at Jet Propulsion Laboratory. Complex organic chemistry in CM matrices includes amino acids, polycyclic aromatic hydrocarbons, and insoluble organic matter characterized by spectrometers and mass spectrometers at Scripps Institution of Oceanography, University of Hawaiʻi, and Institut de Planétologie et d'Astrophysique de Grenoble. Laboratory experiments at Lawrence Livermore National Laboratory and Oak Ridge National Laboratory model synthesis pathways for prebiotic organics under parent body conditions.
Models propose that CM parent bodies accreted in the outer regions of the protoplanetary disk and experienced limited thermal metamorphism but extensive aqueous alteration, scenarios developed by theoreticians at Caltech, Princeton University, and University of Arizona. Dynamical links have been proposed between CM-like materials and primitive asteroids observed by the NEOWISE and Hubble Space Telescope programs, and to potential source bodies sampled by Hayabusa2 and targeted by Lucy planning. Geochemical comparisons by teams at Southwest Research Institute and Johnson Space Center inform constraints on parent body size, porosity, and the timing of alteration relative to short-lived radionuclide heating such as from 26Al decay studied by Sumitomo Heavy Industries-funded groups.
Prominent CM specimens include Murchison meteorite (Australia), Mighei meteorite (Ukraine), Alais meteorite (France), Sutter's Mill (United States), and Tagish Lake meteorite (Canada) — each studied by consortia at Monash University, University of Manchester, University of Alberta, California Institute of Technology, and Imperial College London. These falls and finds have provided key sample suites curated by institutions such as the Natural History Museum, London, Smithsonian Institution, and National Institute of Polar Research for multidisciplinary studies spanning mineralogy, isotopes, and organic chemistry.
CM chondrites are pivotal for testing hypotheses about volatile delivery to terrestrial planets, origins of water and organics on Earth, and preservation of presolar grains identified by researchers at University of Bern and Washington University in St. Louis. Analytical methods applied include scanning electron microscopy at Argonne National Laboratory, secondary ion mass spectrometry at University of Colorado Boulder, synchrotron X-ray diffraction at Brookhaven National Laboratory, transmission electron microscopy at Lawrence Berkeley National Laboratory, and nuclear magnetic resonance at University of Cambridge. Collaborative programs involving NASA, JAXA, ESA, and academic partners continue to integrate CM chondrite studies with space mission data to refine models of Solar System chemical evolution.
Category:Meteorites