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Physical Processing of Cometary NucleiCometary nuclei preserve a cosmo-chemical record of conditions and processes in the primordial solar nebula, and possibly even the interstellar medium. However, that record is not perfectly preserved over the age of the solar system due to a variety of physical processes which act to modify cometary surfaces and interiors. Possible structural and/or internal processes include: collisional accretion, disruption, and reassembly during formation; internal heating by long and short-lived radionuclides; amorphous to crystalline phase transitions, and thermal stresses. Identified surface modification processes include: irradiation by galactic cosmic rays, solar protons, UV photons, and the Sun's T Tauri stage mass outflow; heating by passing stars and nearby supernovae; gardening by debris impacts; the accretion of interstellar dust and gas and accompanying erosion by hypervelocity dust impacts and sputtering; and solar heating with accompanying crust formation. These modification processes must be taken into account in both the planning and the interpretation of the results of a Comet Nucleus Sample Return Mission. Sampling of nuclei should be done at as great a depth below the surface crust as technically feasible, and at vents or fissures leading to exposed volatiles at depth. Samples of the expected cometary crust and near-surface layers also need to be returned for analysis to achieve a better understanding of the effects of these physical processes. We stress that comets are still likely less modified dm any other solar system bodies, but the degree of modification can vary greatly from one comet to the next.
Document ID
19980218972
Acquisition Source
Headquarters
Document Type
Conference Paper
Authors
Weissman, Paul R.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA United States)
Stern, S. Alan
(Colorado Univ. Boulder, CO United States)
Date Acquired
August 18, 2013
Publication Date
December 1, 1997
Publication Information
Publication: Analysis of Returned Comet Nucleus Samples
Subject Category
Astrophysics
Funding Number(s)
CONTRACT_GRANT: NGT-50236
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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