Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p42a..01b&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P42A-01
Mathematics
Logic
[3694] Mineralogy And Petrology / Instruments And Techniques, [6000] Planetary Sciences: Comets And Small Bodies, [6040] Planetary Sciences: Comets And Small Bodies / Origin And Evolution
Scientific paper
The ongoing analyses of samples returned from Wild 2, an active Jupiter Family Comet, have provided unexpected insight into the origin of short period comets and the radial migration of solids in the solar nebula. Instead of a comet dominated by presolar interstellar grains, the samples reveal that this comet is dominated by nebular materials that are also found in primitive meteorites. The samples contain abundant by high temperature materials, including chondrule and Calcium Aluminum Inclusion (CAI) -like fragments that are closely analogous if not identical to meteoritic components. It appears that analyzed Wild 2 solids were produced in the "rock factory" regions of the inner solar nebula where chondrules formed and that they were then transported past the orbit of Neptune where they accreted along with ice and organics to form comet Wild 2. In these inner nebula regions, >99% of the presolar were destroyed by nebular processes. The major comet solids formed by high temperature (1000-2000 C) processes, such as those that formed chondrules, and not the mild solid-state transformation processes that are commonly evoked to explain the presence of crystalline materials that are astronomically observed around other stars. Four presolar grains have been discovered in the samples but it is clear that isotopically anomalous presolar grains are a minor fraction of the comet. It seems likely that the cometary rocky components returned by the Stardust mission are a sample of a ubiquitously distributed flow of nebular solids that was accreted by all bodies including planets and meteorite parent bodies. They are cosmic sediments that reached and dominated the edge of the solar nebula. A primary difference between asteroids and the rocky content of comets is that comets are dominated by this widely distributed component while asteroids are dominated by locally made materials whose chemical, mineralogical and isotopic properties that give meteorite classes their distinctive properties. It seems likely the cometary solids are a wide sampling of materials produced in the solar nebula. While the volatile contents may vary it seems likely that the rocky components of comets and are similar mixtures, cosmic sediments that were transported tens of AU in the solar nebula. Most of the studied cometary solids are a complex mix of pristine minerals and glass whose lack of equilibration, even on micron scales, suggests that they are not altered inside the comet. The comet seems to be a mix of uequilibrated materials that are as unprocessed as the least-altered meteorites. The comet does contain rare magnetite, cubanite and other phases that, in meteorites, are associated aqueous alteration but the dominant comet phases are anhydrous. It is not clear if these potentially secondary materials were made in peculiar regions of the comet or if they were inherited from other bodies. The results of this mission reiterate the importance of sample return to study primitive bodies. Without laboratory studies often done at the micron and submicron scale, such complex materials could not possibly reveal the key information that they contain on early solar system and pre-solar system processes. The methods for studying these remarkable samples have significantly evolved even over the five years that they have been available for study.
Brownlee Don E.
Team Stardust
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