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Paper: Implications of 26Al in Nebular Dust: Formation of Chondrules by Disruption of Molten Planetesimals
Volume: 341, Chondrites and the Protoplanetary Disk
Page: 915
Authors: Sanders, I.S.; Taylor, G.J.
Abstract: At the start of the solar system, 26Al and 60Fe in nebular dust stored perhaps seven times more radioactive energy than the amount needed to melt the dust. Hence, planetesimals that accreted during the first two million years (Myr) almost certainly melted. Numerical modeling suggests that large bodies (e.g., radius = 50 km) rapidly became globes of convecting magma encased within thin rigid crusts. We believe that many such planetesimals populated the protoplanetary disk at this time, colliding and showering the nebula intermittently with cascades of molten droplets that froze and later accreted to other planetesimals. Near-total melting would have meant that the droplets had primitive chemistry, not unlike that of chondrules. We suggest that impact splashing happened for as long as active heating kept the crusts thin, perhaps for the first 2.5 Myr, and that accretion and meltdown destroyed most droplets that were made during the first 1.5 Myr. It may be no coincidence that chondrule ages cluster between 1.5 and 2.5 Myr. These observations invite research on the detailed evolution of molten planetesimal interiors, and the evolution of post-impact plumes. We anticipate that the results of such research will be reconcilable with many aspects of chondrules, including their chemistry, sizes, textures, associated dust, moderately volatile element abundances, inferred cooling rates, and the bulk chemistry of their host meteorites.
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