LINK<\/strong><\/a><\/p>\n\n\n\n“We report on the isotopic, chemical, and structural properties of four O\u2010rich presolar grains identified in situ in the Adelaide ungrouped C2, LaPaZ Icefield (LAP) 031117 CO3.0, and Dominion Range (DOM) 08006 CO3.0 chondrites. All four grains have oxygen\u2010isotopic compositions consistent with origins in the circumstellar envelopes (CSE) of low\u2010mass O\u2010rich stars evolved along the red\u2010giant and asymptotic\u2010giant branch (RGB, AGB, respectively) of stellar evolution. Transmission electron microscope (TEM) analyses, enabled by focused\u2010ion\u2010beam scanning electron microscope extraction, show that the grain from Adelaide is a single\u2010crystal Mg\u2010Al spinel, and comparison with equilibrium thermodynamic predictions constrains its condensation to 1500 K assuming a total pressure \u226410\u22123 atm in its host CSE. In comparison, TEM analysis of two grains identified in the LAP 031117 chondrite exhibits different microstructures. Grain LAP\u201081 is composed of olivine containing a Ca\u2010rich and a Ca\u2010poor domain, both of which show distinct orientations, suggesting changing thermodynamic conditions in the host CSE that cannot be precisely constrained. LAP\u2010104 contains a polycrystalline assemblage of ferromagnesian silicates similar to previous reports of nanocrystalline presolar Fe\u2010rich silicates that formed under nonequilibrium conditions. Lastly, TEM shows that the grain extracted from DOM 08006 is a polycrystalline assemblage of Cr\u2010bearing spinel. The grains occur in different orientations, likely reflecting mechanical assembly in their host CSE. The O\u2010isotopic and Cr\u2010rich compositions appear to point toward nonequilibrium condensation. The spinel is surrounded by an isotopically solar pyroxene lacking long\u2010range atomic order and could have served as a nucleation site for its condensation in the interstellar medium or the inner solar protoplanetary disk.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Thomas J. Zega, Pierre Haenecour, Christine Floss Meteoritics & Planetary Science LINK “We report on the isotopic, chemical, and structural properties of four O\u2010rich presolar grains identified in situ in the Adelaide ungrouped C2, LaPaZ…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9,19,76],"tags":[5270,1814,973,1746,1853,5010],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/20698"}],"collection":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=20698"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/20698\/revisions"}],"predecessor-version":[{"id":20699,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/20698\/revisions\/20699"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=20698"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=20698"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=20698"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}