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Science 21 September 2007:
Vol. 317. no. 5845, pp. 1706 - 1709
DOI: 10.1126/science.1143987
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Reports

A Closer Look at Water-Related Geologic Activity on Mars

A. S. McEwen,1* C. J. Hansen,2 W. A. Delamere,3 E. M. Eliason,1 K. E. Herkenhoff,4 L. Keszthelyi,4 V. C. Gulick,5 R. L. Kirk,4 M. T. Mellon,6 J. A. Grant,7 N. Thomas,8 C. M. Weitz,9 S. W. Squyres,10 N. T. Bridges,2 S. L. Murchie,11 F. Seelos,11 K. Seelos,11 C. H. Okubo,1 M. P. Milazzo,1 L. L. Tornabene,1 W. L. Jaeger,4 S. Byrne,1 P. S. Russell,8 J. L. Griffes,7 S. Martínez-Alonso,6 A. Davatzes,5 F. C. Chuang,9 B. J. Thomson,2 K. E. Fishbaugh,12 C. M. Dundas,1 K. J. Kolb,1 M. E. Banks,1 J. J. Wray10

Water has supposedly marked the surface of Mars and produced characteristic landforms. To understand the history of water on Mars, we take a close look at key locations with the High-Resolution Imaging Science Experiment on board the Mars Reconnaissance Orbiter, reaching fine spatial scales of 25 to 32 centimeters per pixel. Boulders ranging up to ~2 meters in diameter are ubiquitous in the middle to high latitudes, which include deposits previously interpreted as finegrained ocean sediments or dusty snow. Bright gully deposits identify six locations with very recent activity, but these lie on steep (20° to 35°) slopes where dry mass wasting could occur. Thus, we cannot confirm the reality of ancient oceans or water in active gullies but do see evidence of fluvial modification of geologically recent mid-latitude gullies and equatorial impact craters.

1 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.
2 Jet Propulsion Laboratory, Pasadena, CA 91109, USA.
3 Delamere Support Systems, Boulder, CO 80304, USA.
4 U.S. Geological Survey, Flagstaff, AZ 86001, USA.
5 NASA Ames Research Center/SETI Institute, Moffett Field, CA 94035, USA.
6 University of Colorado, Boulder, CO 80309, USA.
7 Smithsonian Center for Earth and Planetary Studies, Washington, DC 20650, USA.
8 University of Bern, Bern, Switzerland.
9 Planetary Science Institute, Tucson, AZ 85719, USA.
10 Cornell University, Ithaca, NY 14853, USA.
11 Applied Physics Laboratory, Laurel, MD 20723, USA.
12 International Space Science Institute, Bern, Switzerland.

* To whom correspondence should be addressed. E-mail: mcewen{at}lpl.arizona.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Recent bright gully deposits on Mars: Wet or dry flow?.
J. D. Pelletier, K. J. Kolb, A. S. McEwen, and R. L. Kirk (2008)
Geology 36, 211-214
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