| Title: | Thermal metamorphism of CM chondrites: A dehydroxylation-based peak-temperature thermometer and implications for sample return from asteroids Ryugu and Bennu |
| Address: | "Department of Earth and Environmental Sciences Michigan State University 288 Farm Lane, Room 207, Natural Sciences Building East Lansing Michigan 48824-1115 USA. Division of Meteorites Department of Mineral Sciences National Museum of Natural History Smithsonian Institution Washington District of Columbia 20013-7012 USA. X12 Astromaterials Research and Exploration Science NASA Johnson Space Center Houston Texas 77058 USA" |
| ISSN/ISBN: | 1086-9379 (Print) 1945-5100 (Electronic) 1086-9379 (Linking) |
| Abstract: | "The target bodies of C-complex asteroid sample return missions are carbonaceous chondrite-like near-Earth asteroids (NEAs), chosen for the abundance and scientific importance of their organic compounds and 'hydrous' (including hydroxylated) minerals, such as serpentine-group phyllosilicates. Science objectives include returning samples of pristine carbonaceous regolith from asteroids for study of the nature, history, and distribution of its constituent minerals, organic material, and other volatiles. Heating after the natural aqueous alteration that formed the abundant phyllosilicates in CM and similar carbonaceous chondrites dehydroxylated them and altered or decomposed other volumetrically minor constituents (e.g., carbonates, sulfides, organic molecules; Tonui et al. 2003, 2014). We propose a peak-temperature thermometer based on dehydroxylation as measured by analytical totals from electron probe microanalysis (EPMA) of matrices in a number of heated and aqueously altered (but not further heated) CM chondrites. Some CM lithologies in Maribo and Sutter's Mill do not exhibit the matrix dehydroxylation expected for surface temperatures expected from insolation of meteoroids with their known orbital perihelia. This suggests that insolated-heated meteoroid surfaces were lost by ablation during passage through Earth's atmosphere, and that insolation-heated material is more likely to be encountered among returned asteroid regolith samples than in meteorites. More generally, several published lines of evidence suggest that episodic heating of some CM material, most likely by impacts, continued intermittently and locally up to billions of years after assembly and early heating of ancestral CM chondrite bodies. Mission spectroscopic measures of hydration can be used to estimate the extent of dehydroxylation, and the new dehydroxylation thermometer can be used directly to select fragments of returned samples most likely to contain less thermally altered inventories of primitive organic molecules" |
| Notes: | "PubMed-not-MEDLINEVelbel, Michael A Zolensky, Michael E eng 2021/07/16 Meteorit Planet Sci. 2021 Mar; 56(3):546-585. doi: 10.1111/maps.13636. Epub 2021 Apr 8" |
