Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.c12c..07m&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #C12C-07
Physics
1863 Snow And Ice (1827), 6225 Mars
Scientific paper
Until recently, indications of the presence of ice in the near surface of Mars, outside the polar caps, has depended upon the interpretation of morphology from imaging data. Early work in this area was based primarily on Viking orbiter images where several large landforms (100s to 1000s of meters in scale) were interpreted to be related to the presence of ice in the regolith or upper crust. These include lineated valley fill, concentric crater fill, softened terrain, and polygons, and are typically found between the latitudes of 30° -60° N and S. Without direct measurements of the presence of water, the interpretations rely on analogies with Earth's periglacial and glacial morphologies as well as geophysical modeling of ice-rich soils and crustal material. New spacecraft data from the Mars Global Surveyor and Mars Odyssey missions have significantly added to the family of morphologies with ground-ice affinities. From the high spatial resolution images acquired by Mars Orbiter Camera (MOC) a new array of polygons have been detected which range in size from 25-200 m and show strong latitudinal gradients above 50° . A possibly related morphology exhibiting a regularly spaced surface texture resembling the texture of a basketball is also found in these high latitudes. A number of morphologies indicating viscous flow on steep slopes are found in the mid-latitudes and are consistent with an ice-rich soils deforming under martian surface conditions. A continuous deposit, meters-thick and interpreted to be ice rich is observed at latitudes above 60° , but that is in a degraded condition at lower latitudes (formerly ice-rich) and absent in the equatorial regions (within 30° ). The neutron spectrometer on the Odyssey spacecraft made direct measurements of hydrogen which shows clearly the presence of high water-ice abundance (>70% by volume) in the surface soils in the northern and southern latitudes above 60° . This critical observation ties in well with theoretical modeling of ice stability under current martian surface conditions. The array of morphologies interpreted to be ice-rich are thus strongly supported by direct measurements of water ice for those observed at latitudes >60° and for those at lower latitudes for conditions in the past when ice was stable to lower latitudes. This array of landforms provides an excellent research environment to investigate periglacial features formed in a very cold environment with long term climate change.
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