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Originally published in Science Express on 1 November 2007
Science 16 November 2007:
Vol. 318. no. 5853, pp. 1125 - 1128
DOI: 10.1126/science.1148112
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Reports

Radar Sounding of the Medusae Fossae Formation Mars: Equatorial Ice or Dry, Low-Density Deposits?

Thomas R. Watters,1* Bruce Campbell,1 Lynn Carter,1 Carl J. Leuschen,2 Jeffrey J. Plaut,3 Giovanni Picardi,4 Roberto Orosei,4 Ali Safaeinili,3 Stephen M. Clifford,5 William M. Farrell,6 Anton B. Ivanov,3 Roger J. Phillips,7 Ellen R. Stofan8

The equatorial Medusae Fossae Formation (MFF) is enigmatic and perhaps among the youngest geologic deposits on Mars. They are thought to be composed of volcanic ash, eolian sediments, or an ice-rich material analogous to polar layered deposits. The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument aboard the Mars Express Spacecraft has detected nadir echoes offset in time-delay from the surface return in orbits over MFF material. These echoes are interpreted to be from the subsurface interface between the MFF material and the underlying terrain. The delay time between the MFF surface and subsurface echoes is consistent with massive deposits emplaced on generally planar lowlands materials with a real dielectric constant of ~2.9 ± 0.4. The real dielectric constant and the estimated dielectric losses are consistent with a substantial component of water ice. However, an anomalously low-density, ice-poor material cannot be ruled out. If ice-rich, the MFF must have a higher percentage of dust and sand than polar layered deposits. The volume of water in an ice-rich MFF deposit would be comparable to that of the south polar layered deposits.

1 Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, DC 20560, USA.
2 Center for Remote Sensing of Ice Sheets, University of Kansas, Lawrence, KS 66045, USA.
3 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
4 Infocom Department, "La Sapienza" University of Rome, 00184 Rome, Italy.
5 Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, USA.
6 NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA1.
7 Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, USA.
8 Proxemy Research, Laytonsville, MD 20882, USA.

* To whom correspondence should be addressed. E-mail: watterst{at}si.edu

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