Ground Ice in the Martian Regolith

Ruslan O. Kuzmin

The long-term existence of extremely cold climate on Mars has led to strong global freezing through upper layers of the planet's crust that has resulted in formation of the global permafrost shell - cryolithosphere. In accordance with the modern thermal regime of the Martian surface and the reasonable values of the planet's heat flow, the thickness of the cryolithosphere may approach 1-2 km in the equatorial zone and 5-6 km in the polar regions. In the presence of such a huge scale of cryolithosphere, most of the Martian water abundance could be captured primarily within the permafrost shell in the form of ground ice and possibly salt solutions. It is not excluded that some amount of the liquid and solid phases of CO2 (plus clathrate) may also be contained in the cryolithosphere.

The long-term and high-amplitude oscillation of the planetary obliquity values have caused a periodic redistribution of the ground ice within the surface layer of the cryolithosphere due to active processes of its condensation and sublimation. At present and lower (< 25°) values of Mars obliquity the ground ice is stable in the surficial regolith layer of both hemispheres only at latitudes poleward of 45° and it is entirely unstable in the equatorial zone, where it is sublimed from the regolith down to depths of hundreds of meters. At larger obliquity values (> 30°) ice becomes stable within the surface layer of the equator down to a depth of a couple of tens of meters.

On Mars there are different types of features whose morphologic patterns (rampart craters, debris flow, lobate debris aprons, terrain softening and polygonal terrains) certainly indicate the presence of ground ice in the Martian regolith. Detailed studies of the rampart impact craters on Mars (as indicators of the ground ice excavation) have shown that the structure of the cryolithosphere as well as the relative ice content distribution within the frozen regolith are characterized by distinct latitudinal zonality and by the presence of a desiccated regolith layer within the equatorial region and at mid latitudes.

This chapter presents an overview of the main characteristics of the Martian cryolithosphere, the particularities of its structure and the potential water amount within the cryogenic shell of the planet. The ground ice stability on Mars under present and past climatic conditions as well as the observed geomorphic manifestations of the ground ice presence in the surface regolith are also the focus of the chapter. Further, the results of the studies of the polygonal terrain distribution on Mars and the correlation of the results with the global map of the highest hydrogen content within a 1-2 m thick surface regolith layer based on Mars Odyssey HEND (High Energy Neutron Detector) data have also been considered here.

R.O. Kuzmin, Ground Ice in the Martian Regolith. In: Adv. Astrobiol. Biogeophys., pp. 155-189 (2005) springerlink.com

Water on Mars and Life, Tetsuya Tokano (ed.), © Springer-Verlag Berlin Heidelberg 2005

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