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Iron alteration minerals in the visible and near-infrared spectra of low-albedo asteroidsAbsorption features centered near 0.60-0.65 and 0.80-0.90 micrometers have been identified in the spectra of five low-albedo main-belt and outer-belt asteroids. These absorption features are attributed respectively to the (6)A(sub 1) goes to (4)T(sub 2)(G) and (6)A(sub 1) goes to (4)T(sub 1)(G) charge transfer transitions in minerals such as goethite, hematite, and jarosite that are products of the aqueous alteration of anhydrous silicates. A shoulder near 0.63 micrometers has also been identified in the absorption feature centered near 0.7 micrometers attributed to oxidized iron in phyllosilicates found predominantly in C- and G-class asteroids reflectance spectra. The coexistence of iron oxides with phyllosilicates in asteroids believed to have undergone aqueous alteration would be expected based upon analogy with terrestrial aqueous alteration and the observed mineralogy of carbonaceous chondrites. The number of low-albedo asteroids having only iron alteration absorption features compared to the number of low-albedo asteroids having spectral characteristics indicative of phyllosilicates is small. Either the conditions under which these asteroids formed are rare, or the iron alteration minerals could be formed in the interiors of objects where phyllosilicates dominate the surface mineralogy.
Document ID
19950043341
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Vilas, Faith (NASA Johnson Space Center Houston, TX, United States)
Jarvis, Kandy S. (Wright State Univ. Dayton, OH, United States)
Gaffey, Michael J. (Rensselaer Polytechnic Inst. Troy, NY, United States)
Date Acquired
August 16, 2013
Publication Date
June 1, 1994
Publication Information
Publication: Icarus
Volume: 109
Issue: 2
ISSN: 0019-1035
Subject Category
LUNAR AND PLANETARY EXPLORATION
Funding Number(s)
CONTRACT_GRANT: NAGW-748
CONTRACT_GRANT: NAGW-642
Distribution Limits
Public
Copyright
Other