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Abundant Solar Nebula Solids in CometsComets have been proposed to consist of unprocessed interstellar materials together with a variable amount of thermally annealed interstellar grains. Recent studies of cometary solids in the laboratory have shown that comets instead consist of a wide range of materials from across the protoplanetary disk, in addition to a minor complement of interstellar materials. These advances were made possible by the return of direct samples of comet 81P/Wild 2 coma dust by the NASA Stardust mission and recent advances in microscale analytical techniques. Isotopic studies of 'cometary' chondritic porous interplanetary dust particles (CP-IDPs) and comet 81P/Wild 2 Stardust samples show that preserved interstellar materials are more abundant in comets than in any class of meteorite. Identified interstellar materials include sub-micron-sized presolar silicates, oxides, and SiC dust grains and some fraction of the organic material that binds the samples together. Presolar grain abundances reach 1 weight percentage in the most stardust-rich CP-IDPs, 50 times greater than in meteorites. Yet, order of magnitude variations in presolar grain abundances among CP-IDPs suggest cometary solids experienced significant variations in the degree of processing in the solar nebula. Comets contain a surprisingly high abundance of nebular solids formed or altered at high temperatures. Comet 81P/Wild 2 samples include 10-40 micron-sized, refractory Ca- Al-rich inclusion (CAI)-, chondrule-, and ameboid olivine aggregate (AOA)-like materials. The O isotopic compositions of these refractory materials are remarkably similar to their meteoritic counterparts, ranging from 5 percent enrichments in (sup 16) O to near-terrestrial values. Comet 81P/Wild 2 and CP-IDPs also contain abundant Mg-Fe crystalline and amorphous silicates whose O isotopic compositions are also consistent with Solar System origins. Unlike meteorites, that are dominated by locally-produced materials, comets appear to be composed of materials that were formed across a wide swath of the early protoplanetary disk.
Document ID
20160007877
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Messenger, S.
(NASA Johnson Space Center Houston, TX, United States)
Keller, L. P.
(NASA Johnson Space Center Houston, TX, United States)
Nakamura-Messenger, K.
(NASA Johnson Space Center Houston, TX, United States)
Nguyen, A. N.
(Jacobs Technologies Engineering Science Contract Group Houston, TX, United States)
Clemett, S.
(Jacobs Technologies Engineering Science Contract Group Houston, TX, United States)
Date Acquired
June 23, 2016
Publication Date
June 26, 2016
Subject Category
Lunar And Planetary Science And Exploration
Report/Patent Number
JSC-CN-36139
Meeting Information
Meeting: Goldschmidt Conference (Goldschmidt 2016)
Location: Yokohama
Country: Japan
Start Date: June 26, 2016
End Date: July 1, 2016
Sponsors: European Association of Geochemistry, Geochemical Society, Geochemical Society of Japan, Japan Agency for Marine-Earth Science and Technology
Distribution Limits
Public
Copyright
Public Use Permitted.
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