^1,2Mabel L. Gray,^1,2,3Michael K. Weisberg,^1,2,3Steven J. Jaret,^1,2Denton S. Ebel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14287]
¹Department Earth and Environmental Sciences, CUNY Graduate Center, New York, New York, USA
²Department Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
³Department Physical Sciences, Kingsborough College CUNY, Brooklyn, New York, USA
Published by arrangement with John Wiley & Sons

The enstatite chondrite class is known to have complex thermal histories, often interpreted to include impact melting and shock metamorphism. Highly equilibrated (type 6) EH group enstatite chondrites are rare and thought to have formed through collisional heating. We studied two EH6 chondrites, NWA 7976 and NWA 12945, for their textural, chemical, and mineralogical characteristics. The samples we studied contain subhedral to anhedral grains of enstatite and plagioclase, suggesting solid-state recrystallization. They show low degrees of shock and no evidence of shock melting. Additionally, the ubiquitous occurrence of daubréelite exsolution lamellae in troilite and the Ni content of schreibersite suggest slow cooling at greater burial depths in the parent body, rather than rapid cooling as a result of an impact event. Based on the characteristics and scarcity of type 6 EH chondrites, and the ubiquitous shock effects and melt rocks in the enstatite chondrite class, we conclude that the unshocked NWA 7976 and NWA 12945 were formed by heat derived from impact melt sheets, analogous to contact metamorphism.

^1,2Matthew J. Genge,²Natasha Almeida,³Matthias Van Ginneken,⁴Lewis Pinault,⁵Louisa J. Preston,³Penelope J. Wozniakiewicz,^6,7Hajime Yano
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14288]
¹Department of Earth Science and Engineering, Imperial College London, London, UK
²Planetary Materials Group, Natural History Museum, London, UK
³Centre for Astrophysics and Planetary Science, Dept. Physics and Astronomy, University of Kent, Canterbury, Kent, UK
⁴Department of Earth and Planetary Sciences, Birkbeck College, London, UK
⁵Department of Space and Climate Physics, Mullard Space Science Laboratory, University College London, Surrey, UK
⁶Department of Interdisciplinary Space Science, Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara, Kanagawa, Japan
⁷Space and Astronautical Science, Graduate Institute for Advanced Studies, SOKENDAI, Sagamihara, Kanagawa, Japan
Published by arrangement with John Wiley & Sons

The presence of microorganisms within meteorites has been used as evidence for extraterrestrial life, however, the potential for terrestrial contamination makes their interpretation highly controversial. Here, we report the discovery of rods and filaments of organic matter, which are interpreted as filamentous microorganisms, on a space-returned sample from 162173 Ryugu recovered by the Hayabusa 2 mission. The observed carbonaceous filaments have sizes and morphologies consistent with microorganisms and are spatially associated with indigenous organic matter. The abundance of filaments changed with time and suggests the growth and decline of a prokaryote population with a generation time of 5.2 days. The population statistics indicate an extant microbial community originating through terrestrial contamination. The discovery emphasizes that terrestrial biota can rapidly colonize extraterrestrial specimens even given contamination control precautions. The colonization of a space-returned sample emphasizes that extraterrestrial organic matter can provide a suitable source of metabolic energy for heterotrophic organisms on Earth and other planets.