LPI Scientist Part of Team Reporting Evidence of a Massive Ice Deposit
November 29, 2007
Planetary scientists, utilizing a sophisticated ground-penetrating radar onboard the European Space Agency’s Mars Express orbiting spacecraft, have identified what they believe is a massive deposit of water ice, mixed with dust or volcanic ash, near the martian equator. Their results were published in the November 16 issue of the journal Science.
Dr. Stephen Clifford of the Lunar and Planetary Institute (LPI) in Houston, Texas, one of the coauthors of the study, described the results as “Exciting, providing further evidence that a vast amount of water as ice, and possibly even groundwater, may be stored beneath the martian surface.”
The findings are based on analysis of data obtained from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). This instrument, which has been in operation since June 2005, utilizes low-frequency radar to investigate the nature of the martian subsurface to depths of up to several miles. The radar pulses emitted by MARSIS are sensitive to the differences in electromagnetic properties that characterize various geologic materials, ice, and especially liquid water.
When a radar pulse encounters the boundary between different materials, part of the signal is reflected back to the spacecraft and part continues to propagate deeper into the subsurface, with the strength of the reflection proportional to the difference in electromagnetic properties. The time that elapses between the transmission of a pulse and the reception of a reflected signal provides a measure of how far below the surface the reflection occurred.
Using this technique, MARSIS scientists investigated a mysterious and extensive equatorial deposit on Mars known as the Medusae Fossae Formation (MFF), finding it to be as much as two miles deep in some areas. Previous investigators have suggested a variety of possible origins for this material, ranging from a massive and geologically recent volcanic ash deposit to a relic polar ice cap from a time, several billion years ago, when the rotational axis of the planet may have been significantly different from that of today.
Based on a comparison of the strength of the echoes received from the top and bottom of this deposit, Clifford and his colleagues concluded that its composition was most consistent with a mixture of large amount of water ice with a small embedded component of dust or volcanic ash — although they could not dismiss the possibility of a very low-density material.
Regardless of which interpretation is chosen, the MFF deposits appear to have characteristics that are unique from other martian deposits.
Mars Express is a Mars exploration mission of the European Space Agency (ESA). The Mars Express mission is dedicated to the orbital study of the atmosphere, surface, and subsurface environments of Mars.
To read the full article:
 Radar Sounding of the Medusae Fossae Formation Mars: Equatorial Ice or Dry, Low-Density Deposits? Thomas R. Watters, Bruce Campbell, Lynn Carter, Carl J. Leuschen, Jeffrey J. Plaut, Giovanni Picardi, Roberto Orosei, Ali Safaeinili, Stephen M. Clifford, William M. Farrell, Anton B. Ivanov, Roger J. Phillips, and Ellen R. Stofan, Science, 318, 1125–1128. Published online 31 October 2007 [DOI: 10.1126/science.1148112].
Last updated January 29, 2008