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Science 2 July 2004:
Vol. 305. no. 5680, pp. 78 - 81
DOI: 10.1126/science.1097549
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Reports

Evidence for Precipitation on Mars from Dendritic Valleys in the Valles Marineris Area

Nicolas Mangold,1* Cathy Quantin,2 Véronique Ansan,1 Christophe Delacourt,2 Pascal Allemand2

Dendritic valleys on the plateau and canyons of the Valles Marineris region were identified from Thermal Emission Imaging System (THEMIS) images taken by Mars Odyssey. The geomorphic characteristics of these valleys, especially their high degree of branching, favor formation by atmospheric precipitation. The presence of inner channels and the maturity of the branched networks indicate sustained fluid flows over geologically long periods of time. These fluvial landforms occur within the Late Hesperian units (about 2.9 to 3.4 billion years old), when Mars was thought to have been cold. Our results suggest a period of warmer conditions conducive to hydrological activity.

1 Laboratoire IDES, UMR CNRS and Université Paris-Sud, Orsay Campus, 91405 Orsay, France.
2 Laboratoire des Sciences de la Terre, UMR CNRS UCB Lyon 1 and ENS Lyon, La Doua Campus, 69622 Villeurbanne, France.

* To whom correspondence should be addressed. E-mail: mangold{at}geol.u-psud.fr

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Science. ISSN 0036-8075 (print), 1095-9203 (online)