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Mars Express
The European Space Agency’s Mars Express orbiter, shown in this artist’s conception, has been circling Mars since 2003. (Spacecraft image credit: ESA / ATG Medialab; Mars: ESA / DLR / FU Berlin, CC BY-SA 3.0 IGO)

Radar readings from the European Space Agency’s Mars Express orbiter point to the location of what appears to be a 12-mile-wide lake of liquid water, buried under about a mile of ice and dust in the Red Planet’s south polar region.

The find is consistent with what scientists have been saying for years about the prospects for subsurface water on Mars, and is likely to give a boost to the search for Red Planet life.

“There are all the ingredients for thinking that life can be there,” Enrico Flamini, project manager for the MARSIS radar instrument on Mars Express, said today during a Rome news conference to discuss the results. “However, MARSIS cannot say anything more.”

The analysis of the MARSIS readings were published today by the journal Science.

Over the past couple of decades, robotic missions have found ample evidence that liquid water existed on Mars billions of years ago. Much of that water was lost as Mars’ protective atmosphere was stripped away, and tons of it are locked up in ice deposits.

Mars radar readings
Mars Express’ MARSIS radar instrument made 29 dedicated observations in a 200-kilometer-square area near Mars’ south pole between 2012 and 2015, indicated on the map at left. The readings turned up a bright radar reflection indicative of liquid water, shown as blue on the map at right. (Context map: NASA / Viking; THEMIS background: NASA / JPL-Caltech / ASU; MARSIS data: ESA / NASA / JPL / ASI / Univ. Rome; R. Orosei et al 2018)

Today, Mars is too cold and dry, and the carbon dioxide atmosphere is too thin, to allow for liquid water at the surface. Deep beneath the surface, however, the weight of overlying soil and glaciers — as well as the potential presence of dissolved salts — could allow water to stay liquid even at what would otherwise be below-freezing temperatures.

Those are the conditions that scientists think exist in the area that they identified.

Between 2012 and 2015, MARSIS’ ground-penetrating radar conducted a survey of a 120-mile-wide (200-kilometer-wide) zone in the Planum Australe region, just beyond Mars’ permanent south polar ice cap.

The readings turned up evidence of a particularly bright radar reflection in a 12-mile-wide (20-kilometer-wide) area. MARSIS’ team interpret that feature as an interface between the overlying ice and a stable body of liquid water that would have to be at least 3 feet (1 meter) thick.

“This subsurface anomaly on Mars has radar properties matching water, or water-rich sediments,” lead study author Roberto Orosei, a principal investigator for the MARSIS experiment, said in an ESA news release. ““This is just one small study area; it is an exciting prospect to think there could be more of these underground pockets of water elsewhere, yet to be discovered.”

MARSIS operations manager Andrea Cicchetti said hints of subsurface anomalies had been detected before, but past attempts to confirm the results were foiled because the radar sampling rates were too low.

Radar readings
Readings from ground-penetrating radar suggest the presence of liquid water about 1.5 kilometers (1 mile) beneath the Martian surface. (ESA / NASA / JPL / ASI / Univ. Rome; R. Orosei et al 2018)

“We had to come up with a new operating mode to bypass some onboard processing and trigger a higher sampling rate and thus improve the resolution of the footprint of our dataset: Now we see things that simply were not possible before,” Cicchetti said.

The subsurface lake could be similar to Antarctica’s Lake Vostok, or to the subsurface seas thought to exist on the Jovian moon Europa or the Saturnian moon Enceladus.

In Lake Vostok’s case, the frigid water serves as a refuge for species that probably got their start millions of years ago. Similarly, if the Martian lake holds life forms, they’re likely to be holdovers from an ancient time when Mars was more habitable.

Future studies will have to confirm the interpretation of the readings, however. A member of the MARSIS team who is not an author of the study, Jeffrey Plaut of NASA’s Jet Propulsion Laboratory, told Science that “the interpretation is plausible, but it’s not quite a slam dunk yet.”

ESA’s ExoMars rover, due for launch in 2020, will be equipped with a drill that can go 6 feet (2 meters) beneath the Red Planet’s surface. But it’d require a far more involved drilling operation to reach the feature identified in the radar readings.

Authors of the Science paper, “Radar Evidence of Subglacial Liquid Water on Mars,” include Orosei, Flamini and Cicchetti, plus S.E. Lauro, E. Pettinelli, M. Coradini, B. Cosciotti, F. Di Paolo, E. Mattei, M. Pajola, F. Soldovieri, M. Cartacci, F. Cassenti, A. Frigeri, S. Giuppi, R. Martufi, A. Masdea, G. Mitri, C. Nenna, R. Noschese, M. Restano and R. Seu.

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