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Originally published in Science Express on 30 November 2005
Science 23 December 2005:
Vol. 310. no. 5756, pp. 1925 - 1928
DOI: 10.1126/science.1122165
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Research Articles
Radar Soundings of the Subsurface of Mars
Giovanni Picardi1,
Jeffrey J. Plaut2*,
Daniela Biccari1,
Ornella Bombaci3,
Diego Calabrese3,
Marco Cartacci1,
Andrea Cicchetti1,
Stephen M. Clifford4,
Peter Edenhofer5,
William M. Farrell6,
Costanzo Federico7,
Alessandro Frigeri7,
Donald A. Gurnett8,
Tor Hagfors9,
Essam Heggy4,
Alain Herique10,
Richard L. Huff8,
Anton B. Ivanov2,
William T. K. Johnson2,
Rolando L. Jordan2,
Donald L. Kirchner8,
Wlodek Kofman10,
Carlton J. Leuschen11,
Erling Nielsen9,
Roberto Orosei12,
Elena Pettinelli14,
Roger J. Phillips15,
Dirk Plettemeier16,
Ali Safaeinili2,
Roberto Seu1,
Ellen R. Stofan17,
Giuliano Vannaroni13,
Thomas R. Watters18 and
Enrico Zampolini3
1 Infocom Department, "La Sapienza" University of Rome, 00184 Rome, Italy.
2 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
3 Alcatel Alenia Space Italia, 00131 Rome, Italy.
4 Lunar and Planetary Institute, Houston, TX 77058, USA.
5 Fakultaet fuer Elektrotechnik und Informationstechnik Ruhr-Universitaet Bochum, D-44780 Bochum, Germany.
6 NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA.
7 Dipartimento di Scienze della Terra, Università degli Studi di Perugia, 06123 Perugia, Italy.
8 Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA.
9 Max Planck Institute for Solar System Research, 37191 Katlenburg-Lindau, Germany.
10 Laboratoire de Planetologie de Grenoble, 38041 Grenoble Cedex, France.
11 Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723, USA.
12 Istituto di Astrofisica Spaziale e Fisica Cosmica, 00133 Rome, Italy
13 Istituto di Fisica dello Spazio Interplanetario, Istituto Nazionale di Astrofisica, 00133 Rome, Italy.
14 Dipartimento di Fisica, University of Rome 3, 00146 Rome, Italy.
15 Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, USA.
16 Fakultaet fuer Elektrotechnik und Informationstechnik, Technische Universitaet Dresden, D-01062 Dresden, Germany.
17 Proxemy Research, Laytonsville, MD 20882, USA.
18 Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, DC 20560, USA.
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Fig. 1. (A) MARSIS data in radargram format for orbit 1855 as it crossed the margin of the NPLD. (B) Simulated MARSIS data if echoes are only from the surface (nadir and off-nadir clutter). (C) MOLA topography along the ground track (red line); elevation is relative to mean planetary radius. MARSIS data at 5 MHz show a split of the strong return into two as the ground track reaches the NPLD (higher terrain to the right). Maximum time delay to the second reflector is 21 µs, equivalent to 1.8-km depth in water ice.
[View Larger Version of this Image (83K GIF file)]
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Fig. 2. Location of the ring structure, northeast Chryse Planitia, in MOLA topographic data (positive east longitude). The inset at top left shows the location of the detailed map on a globe of Mars. Ground track positions are shown as vertical lines (1903 and 1892). Traces of ring structures that match in the two orbits are shown in red (1892) and white (1903).
[View Larger Version of this Image (92K GIF file)]
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Fig. 3. MARSIS data for orbits (A) 1892 (3-MHz band) and (B) 1903 (4-MHz band). Note the multiple arc-shaped reflectors near the center of each panel, and the planar reflector associated with the arcs in orbit 1903 (arrow). (C) Model of the nadir surface and off-nadir clutter for orbit 1903. No arc-like or planar features are predicted in the clutter model. (D) MOLA topography along the ground track of orbit 1903.
[View Larger Version of this Image (58K GIF file)]
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Fig. 4. Schematic showing the geometric relationships of a crater rim and floor in oblique view (left) and as seen in a sounder radargram (right). Note the appearance of multiple parabolic arcs and an associated planar reflector in the radargram. Compare with the radargram of orbit 1903 in Fig. 3.
[View Larger Version of this Image (25K GIF file)]
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