The Equatorial Deposits of Mars: Barchan-Shaped Depressions and Possible Glacial Remnants

Abstract:

There are several distinct deposits near the equator of Mars, including Eumenides Dorsum, that are thought to be of low density. They have been interpreted as ignimbrite or as ice-rich material. It is argued that the equatorial deposits are aeolian or volcanic deposits such as ignimbrite in part because equatorial ice sheets (0 to 30 degrees) seem improbably to some for reasons of the current-day notions of Mars climate history and that we must seek alternatives to glacial interpretations. There is significant latitude and possibilities regarding the history of Mars climate, which might include unimagined incidents and circumstances that can explain how equatorial ice sheets may have formed.

Results from Mars Odyssey's neutron spectrometer ESA’s trace gas orbiter experiment that detects hydrogen in surface material down to one meter indicates that the region of the equator where the deposits are located has a moderate water signature. These results may be consistent with a dust and rock-laden ablation cover typical of terrestrial glaciers, though dust is likely a more important component of the surface lag of ice-rich material on Mars. There is also the possibility that deposits of ice have become intermingled with non-volatile deposits through an overlapping depositional history and by remobilization of material by wind.

Deposits of ice-rich material may erode or ablate somewhat differently than ice-poor material because water may be removed by melting or sublimation. These additional mechanisms of material removal may be reflected in the geomorphology of remnant landforms and erosional features. In fact, barchan-shaped depressions widely indent the deposits and may be a testimony to sublimation and are given special attention.

Three features of the equatorial deposits are considered extraordinary landmarks. The first is the Medusae Fossae canyon, which cuts the southern portion of the Eumenides Dorson/Medusae Fossae deposit. The second is a 100 km wide alcove-shaped feature located on the flank of a deposit. And the third is the deposit of Nicholson Crater, which may represent an ideally isolated and equatorially located ablating ice-rich deposit.