Ice wedge polygons observed on Mars

The planet Mars is known to have abundant water ice, but hidden just below the surface, in the planet's soil.

Since the low quality photographs from the Mariner missions in the 1960s and 1970s, Mars has had landscapes similar to those of the ice-rich permafrost regions on Earth.

However, on Mars, the nature of this ice is unknown: how deep is it ? Does it occur in successive layers ? Does it fill the porosity of the soil ? How and when did it form ?

A study, recently published in the journal Icarus by an international team including LPG researchers Susan Conway and Meven Philippe, looked at soils with polygonal patterns to answer some of these questions. In terrestrial and Martian permafrost soils, polygonal patterned soils are formed as a result of the cracking of ground ice due to temperature changes.

 

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On the left, two corners of ice on the edge of a polygon (side view, sectional view). On the right, seen from above, polygonal patterned floors on Mars (top) and Earth (bottom).
Copyright Earth images : Richard J. Soare, Geography Department, Dawson College, Montreal, Canada. Copyright Mars image (HiRISE ESP_046467_2280) : NASA/JPL/University of Arizona.

 

On Earth, this ice can melt and freeze again on an annual cycle, forming larger and larger "ice wedges" (wedge-shaped pieces of ice) in the ground. Located at the edges of the polygons, they are called "ice wedge polygons". The article published in Icarus magazine presents evidence that ice wedge polygons could also be found on Mars. For the first time, this hypothesis could be validated with a statistical approach.

This result was unexpected, given that the recent climate of the planet is thought to be hostile to thawing and the existence of liquid water.

 

> Reference : Possible ice-wedge polygonisation in Utopia Planitia, Mars and its latitudinal gradient of distribution. Soare R.J.,Conway S.J., Williams J.-P., Philippe M., Mc Keown L.E, Godin E., Hawkswell J., Icarus, in press (pre-proof https://doi.org/10.1016/j.icarus.2020.114208).