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High Silicate Crystalline-to-Amorphous Ratios in Comets C/2001 Q4 (NEAT) and Hale-BoppCrystalline silicates, by their apparent absence in the ISM, are dust grains that experienced high temperatures in the solar nebula. Mg-rich crystalline silicates formed either by condensation from hot nebular gases (1450 K) or by the annealing of Mg-rich amorphous silicates (approx. 1000 K) in shocks in the 5-10 AU region or by radial transport into and out of the hot inner zones, e.g., T(sub d) > 1000 K at r(sub h) < 5 AU, 10(exp -6) - 10(exp -5) M(sub O)/yr, alpha = 10(exp -4) of the early solar nebula. Mg-rich crystalline silicates are found in interplanetary dust particles (IDPs) and produce IR spectral features in many Oort cloud comets. In May 2004, we discovered strong crystalline silicate features in the dynamically new Oort cloud comet C/2001 Q4 (NEAT). Thermal emission modeling of comets Q4 and C/1995 O1 (Hale-Bopp) demonstrate that both these comets have similar, high silicate crystalline-to-amorphous ratios of 2.4 and 2.1, respectively, indicating that these icy planetesimals aggregated from similar reservoirs of material or that crystalline silicates were widely distributed within the comet-forming zone. This argues for efficient annealing mechanisms and radial mixing.
Document ID
20050009927
Acquisition Source
Ames Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Wooden, D. H.
(NASA Ames Research Center Moffett Field, CA, United States)
Harker, D. E.
(California Univ., San Diego La Jolla, CA, United States)
Woodward, C. E.
(Minnesota Univ. Minneapolis, MN, United States)
Date Acquired
August 22, 2013
Publication Date
October 19, 2004
Subject Category
Lunar And Planetary Science And Exploration
Meeting Information
Meeting: Chondrites and the Protoplanetary Disk
Location: Lihue, HI
Country: United States
Start Date: November 8, 2004
End Date: November 11, 2004
Funding Number(s)
OTHER: 344-32-21-04
Distribution Limits
Public
Copyright
Other

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