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Title:
The origin of lunar crater rays
Authors:
Hawke, B. Ray; Blewett, D. T.; Lucey, P. G.; Smith, G. A.; Bell, J. F.; Campbell, B. A.; Robinson, M. S.
Affiliation:
AA(Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii, 1680 East-West Road, Honolulu, HI 96822, USA; ), AB(NovaSol, 1100 Alakea Street, 23rd Floor, Honolulu, HI 96813, USA), AC(Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii, 1680 East-West Road, Honolulu, HI 96822, USA), AD(Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii, 1680 East-West Road, Honolulu, HI 96822, USA), AE(Department of Astronomy, Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853, USA), AF(Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, DC 20560, USA), AG(Center for Planetary Sciences, Northwestern University, 1847 Sheridan Road, Evanston, IL 60208, USA)
Publication:
Icarus, Volume 170, Issue 1, p. 1-16. (Icarus Homepage)
Publication Date:
07/2004
Origin:
ELSEVIER
Keywords:
surface, Impact processes, Cratering, Spectroscopy, Radar
DOI:
10.1016/j.icarus.2004.02.013
Bibliographic Code:
2004Icar..170....1H

Abstract

Lunar rays are filamentous, high-albedo deposits occurring radial or subradial to impact craters. The nature and origin of lunar rays have long been the subjects of major controversies. We have determined the origin of selected lunar ray segments utilizing Earth-based spectral and radar data as well as FeO, TiO2, and optical maturity maps produced from Clementine UVVIS images. These include rays associated with Tycho, Olbers A, Lichtenberg, and the Messier crater complex. It was found that lunar rays are bright because of compositional contrast with the surrounding terrain, the presence of immature material, or some combination of the two. Mature ``compositional'' rays such as those exhibited by Lichtenberg crater, are due entirely to the contrast in albedo between ray material containing highlands-rich primary ejecta and the adjacent dark mare surfaces. ``Immaturity'' rays are bright due to the presence of fresh, high-albedo material. This fresh debris was produced by one or more of the following: (1) the emplacement of immature primary ejecta, (2) the deposition of immature local material from secondary craters, (3) the action of debris surges downrange of secondary clusters, and (4) the presence of immature interior walls of secondary impact craters. Both composition and state-of-maturity play a role in producing a third (``combination'') class of lunar rays. The working distinction between the Eratosthenian and Copernican Systems is that Copernican craters still have visible rays whereas Eratosthenian-aged craters do not. Compositional rays can persist far longer than 1.1 Ga, the currently accepted age of the Copernican-Eratosthenian boundary. Hence, the mere presence of rays is not a reliable indication of crater age. The optical maturity parameter should be used to define the Copernican-Eratosthenian boundary. The time required for an immature surface to reach the optical maturity index saturation point could be defined as the Copernican Period.
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