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Morphological and geographical evidence for the origin of Phobos’ grooves from HRSC Mars Express images

By
John B. Murray
John B. Murray
1
Department of Earth & Environmental Sciences, The Open University, Milton Keynes MK7 6AA, UK
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Jonathan C. Iliffe
Jonathan C. Iliffe
2
Department of Civil, Environmental and Geomatic Engineering, University College London, Gower Street, London WC1E 6BT, UK
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Published:
January 01, 2011

Abstract

The surface of Phobos, the 27×22×18 km inner moon of Mars, is dominated by several families of parallel grooves. At least seven different groups of hypotheses have been advanced to explain their origin, but studies have always been limited by the fact that, until recently, much of Phobos was imaged at a resolution too low to show grooves. Now, however, the High Resolution Stereo Camera (HRSC) on board the European Mars Express mission has made 134 imaging fly-bys past Phobos. The pictures of the previously poorly imaged regions and much of the rest of the satellite have been returned with resolutions down to a few metres, facilitating the construction of a more complete map of the grooves. Each of the seven hypotheses was tested against the new data on groove morphology, positions and orientations, and it was found that six of the previous hypotheses could be discarded. The only hypothesis to pass all tests was that they are chains of secondary impact craters from primary impacts on Mars. An implication of these results is that previous estimates of an unusually thick Phobos regolith of 100–200 m depth are no longer necessary, and our conclusions place no constraints on the interior of Phobos, so recent evidence that Phobos is a ‘rubble pile’ is consistent with our work. The preferred hypothesis also sheds light on the origin of crater chains on Eros, and on impact processes in the early stages of crater excavation.

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Contents

Geological Society, London, Special Publications

Martian Geomorphology

M. R. Balme
M. R. Balme
Open University, UK
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A. S. Bargery
A. S. Bargery
Lancaster University, UK
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C. J. Gallagher
C. J. Gallagher
University College Dublin, Ireland
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S. Gupta
S. Gupta
Imperial College London, UK
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Geological Society of London
Volume
356
ISBN electronic:
9781862396043
Publication date:
January 01, 2011

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