Meteoritics & Planetary Science 47, Nr 12, 2170–2192 (2012) doi: 10.1111/maps.12002 The origin of chondrules and chondrites: Debris from low-velocity impacts between molten planetesimals? Ian S. SANDERS1,* and Edward R. D. SCOTT2 1Department of Geology, Trinity College, Dublin 2, Ireland 2Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Manoa, Honolulu, Hawai’i 96822, USA *Corresponding author. E-mail:
[email protected] (Received 11 June 2012; revision accepted 17 September 2012) Abstract–We investigate the hypothesis that many chondrules are frozen droplets of spray from impact plumes launched when thin-shelled, largely molten planetesimals collided at low speed during accretion. This scenario, here dubbed ‘‘splashing,’’ stems from evidence that such planetesimals, intensely heated by 26Al, were abundant in the protoplanetary disk when chondrules were being formed approximately 2 Myr after calcium-aluminum-rich inclusions (CAIs), and that chondrites, far from sampling the earliest planetesimals, are made from material that accreted later, when 26Al could no longer induce melting. We show how ‘‘splashing’’ is reconcilable with many features of chondrules, including their ages, chemistry, peak temperatures, abundances, sizes, cooling rates, indented shapes, ‘‘relict’’ grains, igneous rims, and metal blebs, and is also reconcilable with features that challenge the conventional view that chondrules are flash-melted dust-clumps, particularly the high concentrations of Na and FeO in chondrules, but also including chondrule diversity, large phenocrysts, macrochondrules, scarcity of dust-clumps, and heating. We speculate that type I (FeO-poor) chondrules come from planetesimals that accreted early in the reduced, partially condensed, hot inner nebula, and that type II (FeO-rich) chondrules come from planetesimals that accreted in a later, or more distal, cool nebular setting where incorporation of water-ice with high D17O aided oxidation during heating.