90 percent water ice at the Mars South Pole

Radar measurements for the first time reveal a more precise quantity and composition of the polar cap

The map shows the thickness of the deposits at the Marssüdpol. © MARSIS / ESA
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The ice at the south pole of Mars contains so much water that it could cover the entire planet in liquid form with an eleven-meter-thick layer. This is the result of a radar measurement of the ESA probe Mars Express now published in Science. In more than 300 individual sections and up to a depth of 3.7 kilometers, the probe shined through the polar ice cap.

The layered ice sheets at the poles of Mars form a bright white cap of a mixture of carbon dioxide and water ice mixed with dust layers. The size of the water ice in this cap has now been demonstrated for the first time by new measurements of the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument on board the Mars probe Mars Express.

90 percent water ice

The results provide valuable clues to the conditions that prevailed in the past on the Red Planet and also to the question of whether there was ever enough liquid water to make life possible. "MARSIS not only gives us the first insights into the underground of Mars in these depths, the details we recognize are also absolutely amazing, " explains Giovanni Picardi from the University of Rome, head of research for radar measurement.

The echo radar received from the stony ground under the layered ice sheet indicates that at least 90 percent of the ice there is frozen water. "The stratified deposits at the south pole of Mars cover an area almost as big as Europe, " said Jeffrey Plaut of the Jet Propulsion Laboratory, one of the researchers involved in the mission. "The amount of water it contained was already appreciated, but never with the reliability it has now achieved thanks to radar measurements.

Crust more firmly than on earth

One region of the ice cap even amazed the researchers: the strong reflections resembled those normally caused by a thin layer of liquid water. But the conditions at the South Pole are so cold that the existence of meltwater here is extremely unlikely. display

The radar measurements also revealed for the first time exactly the shape of the soil surface under the ice. "We did not know exactly where the base of the deposits was, " says Plaut. "Now we can see that the crust was not pushed down by the weight of the ice, as it would be on Earth. Crust and upper mantle are stronger on Mars than on Earth, probably because the inside of the planet is much colder. "

(European Space Agency, 16.03.2007 - NPO)