Mars: Is volcanism still active?

Hot magma could explain the liquid water under the polar icecaps

Stratified ice at the north pole of Mars. Could there be warm magma chambers in the Martian underground? © ESA / DLR / FU Berlin, NASA MGS MOLA Science Team
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Hidden volcanic heat: If there really is liquid water under the polar ice caps of Mars, then there could also be a hot magma chamber underground. Because only with an additional heat source like this, the water could remain liquid there, as researchers have determined. According to their calculations, neither a high salt content nor the pressure of the ice alone is sufficient to explain the melted ice base.

Whether there is still liquid water on the Red Planet today, is highly controversial. Because the cold and the low gas pressure of the atmosphere let any wet immediately freeze or evaporate. However, there is evidence that liquid water could exist, at least temporarily, in craters or salty leaches in the subsurface. In the summer of 2018, radar data also caused a stir, indicating greater amounts of water under the Martian Pole ice cap.

How does the subglacial water remain liquid?

The problem only: What keeps the water liquid under the Martian ice caps, the then study did not answer. Michael Sori and Ali Bramson from the University of Arizona at Tucson now turn to this point. "We asked ourselves: what kind of environment would it take to melt the ice there and what temperatures and geological processes would be necessary?" Says Sori. "Because under normal circumstances it would be much too cold there."

For their study, the researchers created a geophysical model of Martian ice caps. They then added different salty leaches to the bottom of the ice and examined the factors and thresholds above which this leach remains above its freezing point. "Our goal is to create a heat gradient sufficient to melt the underside of the S dpol ice cap, " the researchers said.

Normal Martian conditions are not enough

The result: under today's typical conditions on Mars, the inner warmth of the planet is not even enough to melt the ice of the poles. "Even with the most favorable composition of high salinity and 20 percent dust, a heat flux of 72 watts per square meter would be needed to produce liquid water, " report Sori and Bramson. However, in the best case, the heat flux from the interior of Mars reaches a maximum of 30 watts per square meter. display

The fact that the bottom of the polar ice caps melted only by the pressure of the ice, the salt and the heat of the Mars underground, is therefore almost impossible. But what could have produced this liquid water? In search of a solution, the researchers turned to the geological process, which has already decisively influenced Mars in the past: volcanism.

Scenario for a magma chamber under the south pole of Mars as a source of heat. AGU / GRL, Sori and Bramson

Magma chamber as a heat supplier?

The fact that the red planet was once volcanically active, as evidenced by mighty mountains of fire like the Olympus Mons, but also hidden in the subsoil super volcanoes. Some of the large canyons could also have been formed by lava streams. So far, however, planetary scientists have assumed that volcanic activity on Mars has died out more than a hundred million years ago. But there are also some indications that suggest dormant but possibly even persistent volcanism.

"That could mean that there are still active magma chambers in the subsurface of Mars, and that Mars is not just cold and dead inside, " says Bramson. According to the scientists, the residual heat of these magmatic processes could explain the presence of liquid water under the polar caps of Mars.

If water, then volcanism

According to her calculations, it would have been sufficient if magma had risen up to the Martian crust about 300, 000 years ago. The warmth of this slowly slowing magma could then rise in the course of time and melt on the bottom of the ice. For the required 72 watts per square meter of heat flow, a magma chamber of five kilometers in diameter would be sufficient at a depth of around eight kilometers, according to the researchers.

But that means: If there really is liquid water under the polar ice caps of Mars, then there must also exist a heat source for it. And in the opinion of Sori and Bramson, it can only be based on volcanic heat. "If the interpretation of the radar data proves correct, then there may have been an active magmatism in these areas recently, " the researchers say. More information about this could be provided by the data from the Mars InSight probe, which is currently investigating the heat flow and subsurface of Mars. (Geophysical Research Letters, 2019; doi: 10.1029 / 2018GL080985)

Source: American Geophysical Union

- Nadja Podbregar