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| Paper: |
From Supernovae to Planets: The View from Meteorites and Interplanetary Dust Particles |
| Volume: |
341, Chondrites and the Protoplanetary Disk |
| Page: |
972 |
| Authors: |
Alexander, C.M.O'D. |
| Abstract: |
Chondritic meteorites and IDPs retain a record of the prehistory and early history of the Solar System. Chondrites are derived from the asteroid belt, while IDPs probably have both cometary and asteroidal origins. Chondrites and their components contained relatively high levels of short-lived radionuclides when they formed. Some, like 60Fe, require a stellar source, while others may have formed via energetic particle irradiation in the Solar System. The half-lives of some of the radionuclides are so short (0.1-0.7 My) that if they had a stellar source, this source probably triggered the formation of the Solar System. The high abundance of crystalline circumstellar silicates in IDPs and meteorites, and the relatively low abundance of interstellar organic matter in CI chondrites may result from the thermal processing of interstellar dust seen in YSOs. The oldest dated Solar System objects are the refractory inclusions. The more abundant chondrules seem to have begun forming 1-2 My after refractory inclusions, although there is evidence that chondrules in the CV chondrites began forming contemporaneously with refractory inclusions. Both refractory inclusions and chondrules appear to be the products of transient heating events. The mechanism for making refractory inclusions is uncertain, but in most models refractory inclusions form sunward of the asteroid belt and are then transported outwards either in energetic winds or via turbulent diffusion. At present, the most promising mechanism for making chondrules is shock heating in the asteroid belt. Each chondrite group contains a chemically and/or physically distinct population of chondrules and refractory inclusions. To preserve their distinct chondrule properties from being erased by turbulent diffusion, it is argued that chondrites must have accreted soon after their chondrules formed. However, the variation in the properties of refractory inclusions between chondrites is unexplained. To explain the evidence for aqueous alteration in most chondrites, chondrite formation occurred in the T Tauri phase when temperatures in the asteroid belt allowed for ice to be stable. |
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