LINK<\/strong><\/a><\/p>\n\n\n\n“Aqueously altered carbonaceous astromaterials are dominated by secondary minerals, but a minor fraction of primary, anhydrous silicates and oxides escape alteration, offering insight into the original composition of asteroid parent bodies. We report the mineralogy, petrology, mineral chemistry, and oxygen isotopes of anhydrous minerals\u201450 olivine grains, 12 pyroxene grains, two spinel grains, and one hibonite grain\u2014in aqueously altered particles returned from asteroid Bennu by the OSIRIS-REx mission. These primordial grains are heterogeneously distributed, being more abundant (up to a few area percent for olivine) in less aqueously altered clasts. Olivine is typically forsteritic (Fo100\u2013Fo93), but we found three fayalitic examples (Fo80\u2013Fo75). Of the pyroxenes, seven grains are enstatite (En100\u2013En94); two are enstatite with more Fe (En83 and En87); one is Fe-rich, low-Ca clinopyroxene; one is Mg-rich, aluminous low-Ca pyroxene; and one is high-Al, Ca-rich clinopyroxene. Chromium is present in olivine grains at high abundances (up to 1.3\u2009wt% Cr2O3), indicating that the grains have not experienced significant thermal metamorphism. The olivines fall into two clusters: one with 16O-rich compositions (\u03b418O\u2009=\u2009\u221243 to \u221251\u2030) typical of refractory inclusions in carbonaceous chondrites and one with comparatively 16O-poor compositions (\u03b418O\u2009=\u2009\u221211 to +7.5\u2030) more typical of chondrules. Pyroxenes all fall in the 16O-poor cluster (\u03b418O\u2009=\u2009\u22122.6 to +13.5\u2030). For both olivine and pyroxene, the more Fe-rich examples are associated with heavier oxygen isotope compositions. One isolated spinel grain has an oxygen isotope composition typical of Ca-Al\u2013rich inclusions, whereas a spinel\u2013hibonite object has an unusual oxygen isotope composition consistent with fractionated unknown nuclear (FUN) compositions. Together, our data suggest that Bennu’s parent body accreted a population of finer grained (\u226410\u2009\u03bcm) silicate and oxide grains that as a population are distinct from the anhydrous minerals in most chondrite groups but comparable to those in CI chondrites. The Bennu samples, as well as those from asteroid Ryugu and CI chondrites, appear to have accreted from a distinct reservoir that may have been in the outer protoplanetary disk.”<\/p>\n","protected":false},"excerpt":{"rendered":"
S. S. Russell, I. A. Franchi, T. Salge, X. Zhao, R. H. Jones, A. J. King, N. V. Almeida, P. F. Schofield, H. C. Bates, E. A. Cortes-Calderon, N. Kawasaki, Y. Yurimoto, Y. Marrocchi, G….<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[77,9,552,1184],"tags":[5719,2922,1618,553,4037,3037,1886,1845,644,4899,2036],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/41601"}],"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=41601"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/41601\/revisions"}],"predecessor-version":[{"id":41602,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/41601\/revisions\/41602"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=41601"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=41601"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=41601"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}