New impact craters at five sites in the martian mid-latitudes excavated material from depths of decimeters that has a brightness and color indicative of water ice. Near-infrared spectra of the largest example confirm this composition, and repeated imaging showed fading over several months, as expected for sublimating ice. Thermal models of one site show that millimeters of sublimation occurred during this fading period, indicating clean ice rather than ice in soil pores. Our derived ice-table depths are consistent with models using higher long-term average atmospheric water vapor content than present values. Craters at most of these sites may have excavated completely through this clean ice, probing the ice table to previously unsampled depths of meters and revealing substantial heterogeneity in the vertical distribution of the ice itself.
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Univ Chicago, Dept Geophys Sci, 5734 S Ellis Ave, Chicago, IL 60637 USAUniv Chicago, Dept Geophys Sci, 5734 S Ellis Ave, Chicago, IL 60637 USA
Warren, Alexandra O.
Wilson, Sharon A.
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Smithsonian Inst, Ctr Earth & Planetary Studies, Natl Air & Space Museum, 6th Independence SW, Washington, DC 20560 USAUniv Chicago, Dept Geophys Sci, 5734 S Ellis Ave, Chicago, IL 60637 USA
Wilson, Sharon A.
Howard, Alan
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Planetary Sci Inst, 1700 East Ft Lowell, Tucson, AZ 85719 USAUniv Chicago, Dept Geophys Sci, 5734 S Ellis Ave, Chicago, IL 60637 USA
Howard, Alan
Noblet, Axel
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Univ Western Ontario, Dept Earth Sci, 1151 Richmond St N, London, ON N6A 5B7, CanadaUniv Chicago, Dept Geophys Sci, 5734 S Ellis Ave, Chicago, IL 60637 USA
Noblet, Axel
Kite, Edwin S.
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Univ Chicago, Dept Geophys Sci, 5734 S Ellis Ave, Chicago, IL 60637 USAUniv Chicago, Dept Geophys Sci, 5734 S Ellis Ave, Chicago, IL 60637 USA