{"id":40252,"date":"2026-03-07T09:32:09","date_gmt":"2026-03-07T08:32:09","guid":{"rendered":"https:\/\/karmaka.de\/?p=40252"},"modified":"2026-03-07T09:32:10","modified_gmt":"2026-03-07T08:32:10","slug":"a-prolonged-bombardment-history-of-asteroid-4-vesta-insights-from-u-pb-chronology-of-eucrite-phosphates-and-zircons","status":"publish","type":"post","link":"https:\/\/karmaka.de\/?p=40252","title":{"rendered":"A prolonged bombardment history of asteroid 4 Vesta: insights from U\u2013Pb chronology of eucrite phosphates and zircons<span class=\"badge-status\" style=\"background:#787878\">OPEN ACCESS<\/span>&nbsp;"},"content":{"rendered":"\n<p>M. Koike, Y. Sumiya, R. Kanemaru, B.G. Rider-Stokes, R. Sakai, N. Takahata, K. Sasaki, H. Asanuma, Y. Sano<\/p>\n\n\n\n<p>Geochimica et Cosmochimica Acta, In Press, Journal Pre-proof, Available online 6 March 2026<\/p>\n\n\n\n<p><a href=\"https:\/\/www.sciencedirect.com\/science\/article\/pii\/S0016703726001389\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>LINK +PDF (OPEN ACCESS)<\/strong><\/a><\/p>\n\n\n\n<p class=\"justify-text\">&#8220;Asteroid 4 Vesta is an ancient, differentiated rocky body, whose lithologies are represented on Earth as howardite\u2013eucrite\u2013diogenite meteorites (HEDs). Chronological studies of HEDs provide key constraints on the formation and evolution process of Vesta and offer insights into early Solar System history. Here, we present new U\u2013Pb dataset for Ca-phosphate minerals (apatite and merrillite) and zircon in four eucrite-melt breccias, Northwest Africa (NWA) 13,166, NWA 10,602, NWA 10,603, and NWA 11,576. Zircon grains from the four samples yield a weighted mean 207Pb\/206Pb age of 4556\u202f\u00b1\u202f13\u202fMa (all uncertainties are reported at 2-sigma level), consistent with previously reported ages of old zircons in eucrites (a weighted mean 207Pb\/206Pb age of 4552.6\u202f\u00b1\u202f0.9\u202fMa; n\u202f=\u202f25). Total U\u2013Pb discordia are obtained from co-existing phosphate grains in NWA 13,166 (upper intercept at 4169\u202f+\u202f82\/-83\u202fMa and lower intercept of 72\u202f\u00b1\u202f26\u202fMa) and NWA 10,603 (4234\u202f+\u202f62\/-63\u202fMa and 46\u202f\u00b1\u202f74\u202fMa). Model 207Pb\/206Pb ages of individual phosphate grains range from\u202f\u223c\u202f4370 to\u202f\u223c\u202f4110\u202fMa across the four studied samples. When considered with published data, phosphate 207Pb\/206Pb ages in basaltic eucrites define two distinct populations: an older population with a weighted mean age of 4520.6\u202f\u00b1\u202f5.0\u202fMa (n\u202f=\u202f7), and a younger population with a weighted mean age of 4206\u202f\u00b1\u202f27\u202fMa (n\u202f=\u202f9). The older phosphates likely record prolonged cooling of Vesta\u2019s crust and\/or impact-related reheating at\u202f\u223c\u202f4520\u202fMa. In contrast, the younger phosphates reflect multiple bombardment events at\u202f\u223c\u202f4200\u202fMa. Microstructural observations of phosphate crystals reveal extensive deformation and recrystallization, consistent with impact-resetting of their U\u2013Pb systems. Reported 40Ar\/39Ar ages of HEDs span a broader range, clustering at\u202f\u223c\u202f4490\u202fMa for unbrecciated eucrites, varying between\u202f\u223c\u202f3900\u20132500\u202fMa for brecciated eucrites and howardites, and\u202f\u2264\u202f2400\u202fMa for diogenites. These chronological constraints suggest that Vesta experienced an extended period of bombardment from\u202f\u223c\u202f4200\u202fMa to\u202f\u223c\u202f2500\u202fMa. As suggested by previous studies, the meteoritic record is more consistent with a prolonged and monotonic decline in impact rates beginning in the early stages of Solar System formation, rather than a discrete collisional spike envisioned in the Late Heavy Bombardment hypothesis.&#8221;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>M. Koike, Y. Sumiya, R. Kanemaru, B.G. Rider-Stokes, R. Sakai, N. Takahata, K. Sasaki, H. Asanuma, Y. Sano Geochimica et Cosmochimica Acta, In Press, Journal Pre-proof, Available online 6 March 2026 LINK +PDF (OPEN ACCESS)&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[35,33,186],"tags":[3270,2541,93,1823,212,2553,1866,7092,7093,7094,7091,3443,664,3097,184],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/40252"}],"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=40252"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/40252\/revisions"}],"predecessor-version":[{"id":40253,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/40252\/revisions\/40253"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=40252"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=40252"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=40252"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}