* Astronomy

Title: Northwest Africa 5958: a weakly altered CM-related ungrouped chondrite, not a CI3
Author: Emmanuel Jacquet, Jean-Alix Barrat, Pierre Beck, Florent Caste, Jérôme Gattacceca, Corinne Sonzogni, Matthieu Gounelle

Northwest Africa (NWA) 5958 is a carbonaceous chondrite found in Morocco in 2009. Preliminary chemical and isotopic data leading to its initial classification as C3.0 ungrouped have prompted us to conduct a multi-technique study of this meteorite and present a general description here. The petrography and chemistry of NWA 5958 is most similar to a CM chondrite, with a low degree of aqueous alteration, apparently under oxidizing conditions, and evidence of a second, limited alteration episode manifested by alteration fronts. The oxygen isotopic composition, with Delta^17O = -4.3 per mille, is more 16O-rich than all CM chondrites, indicating, along with other compositional arguments, a separate parent body of origin. We suggest that NWA 5958 be reclassified as an ungrouped carbonaceous chondrite related to the CM group.

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