Recent radar observations from ESA’s Mars Express spacecraft were interpreted as evidence for melting beneath the south polar ice cap of Mars. Now, a duo of researchers from the Lunar and Planetary Laboratory at the University of Arizona argues there needs to be an underground source of heat for liquid water to exist underneath the ice cap. The scientists suggest recent magmatic activity — the formation of a magma chamber within the past few hundred thousand years — must have occurred underneath the Martian surface for there to be enough heat to produce liquid water underneath the thick ice cap. On the flip side, they argue that if there was not recent magmatic activity underneath the surface, then there is not likely liquid water underneath the ice cap.
The south pole of Mars. Image credit: NASA.
Mars has two giant ice sheets at its poles, both a couple of miles thick. On Earth, it is common for liquid water to be present underneath thick ice sheets, with the planet’s heat causing the ice to melt where it meets the crust.
In 2018, Dr. Roberto Orosei of Italy’s Istituto di Radioastronomia, Istituto Nazionale di Astrofisica and colleagues detected a similar phenomenon on Mars.
They claimed radar observations detected evidence of liquid water at the base of Mars’ south polar ice cap. However, they did not address how the liquid water could have gotten there.
Mars is much cooler than Earth so it was unclear what type of environment would be needed to melt the ice at the base of the ice cap.
“We thought there was a lot of room to figure out if [the liquid water] is real, what sort of environment would you need to melt the ice in the first place, what sort of temperatures would you need, what sort of geological process would you need? Because under normal conditions, it should be too cold,” said Dr. Michael Sori, an associate staff scientist in the University of Arizona’s Lunar and Planetary Laboratory.
Dr. Sori and his colleague, Dr. Ali Bramson, first assumed the detection of liquid water underneath the ice cap was correct and then worked to figure out what parameters were needed for the water to exist.
They performed physical modeling of Mars to understand how much heat is coming out of the interior of the planet and if there could be enough salt at the base of the ice cap to melt the ice. Salt lowers the melting point of ice significantly so it was thought that salt could have led to melting at the base of the ice cap.
The model showed salt alone would not raise the temperature high enough to melt the ice. Instead, the researchers propose there needs to be additional heat coming from Mars’ interior.
One plausible heat source would be volcanic activity in the planet’s subsurface.
The team argues that magma from the deep interior of Mars rose towards the planet’s surface about 300,000 years ago. It did not break the surface, like a volcanic eruption, but pooled in a magma chamber below the surface. As the magma chamber cooled, it released heat that melted the ice at the base of the ice sheet. The magma chamber is still providing heat to the ice sheet to generate liquid water today.
The idea of volcanic activity on Mars is not new — there is a lot of evidence of volcanism on the planet’s surface. But most of the volcanic features on Mars are from millions of years ago, leading scientists to believe volcanic activity below and above the planet’s surface stopped long ago.
Dr. Sori and Dr. Bramson, however, propose that there could have been more recent underground volcanic activity. And, if there was volcanic activity happening hundreds of thousands of years ago, there’s a possibility it could be happening today.
“This would imply that there is still active magma chamber formation going on in the interior of Mars today and it is not just a cold, sort of dead place, internally,” Dr. Bramson said.
The study was published in the journal Geophysical Research Letters.
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Michael M. Sori & Ali M. Bramson. Water on Mars, With a Grain of Salt: Local Heat Anomalies Are Required for Basal Melting of Ice at the South Pole Today. Geophysical Research Letters, published online February 12,2019; doi: 10.1029/2018GL080985
