Aqueous Alteration and Accretion of Chondrite Parent Bodies: When and Where

Events such as the Shoemaker−Levy 9 comet impact into Jupiter (July 1994) and the Chelyabinsk meteorite impact in Russia (February 2013) are reminders of the dynamic processes that were part of the formation of our Solar System from a protosolar molecular cloud of interstellar and circumstellar dust and gas. High-temperature (up to 2000 K) transient heating events (e.g. shock waves, current sheets, lightning, etc.) resulted in thermal processing (evaporation, condensation, and melting) of the primordial molecular cloud matter. In general, however, the ambient temperature of the disk decreased radially from the proto-Sun. When temperatures fell below 160 K, water vapor condensed directly into water ice, forming a front known as the “snow line”. The snow line likely did not reside at a single location in the disk, but rather migrated as the luminosity of the proto-Sun, mass accretion rate, and disk opacity all evolved with time. Some models suggest that the snow line could be located at about 5 astronomical units (1 AU = average distance between Earth and the Sun) early in disk evolution, which is not far from Jupiter’s current orbit, but is likely to have been present at 2−3 AU when the disk was just 2−4 My old (Ciesla and Cuzzi 2005).

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