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Fresh hints of hidden lakes put Mars in spotlight

Two years after reporting the detection of a subsurface lake of liquid water near Mars’ south pole, scientists say they’ve gathered further evidence for the existence of that lake — plus three more hidden reservoirs of what’s likely to be super-salty H2O.

Such findings raise new hopes in the search for life beyond Earth in the solar system, although the conditions that’d be required are close to the edge of plausibility.

The new findings, published this week in Nature Astronomy, take advantage of techniques that look at the smoothness as well as the brightness of radar reflections. The research team includes many of the same scientists who were behind the earlier study, including lead author Elena Pettinelli of the University of Rome.

Pettinelli and her colleagues of ground-penetrating radar readings from MARSIS, an instrument on the European Space Agency’s Mars Express orbiter.

Two years ago, the team identified a spot in Ultimi Scopuli, an area within a Martian region called Planum Australe, where the brightness of the radar echoes hinted at a reservoir of liquid water that might lie a mile beneath layers of ice and dust. But the researchers had only a limited amount of observations to go on.

Since then, they’ve added lots more data, and they also took advantage of new techniques that were field-tested to discover lakes hidden beneath the ice of East Antarctica, Greenland and the Canadian Arctic.

The new analysis confirmed readings related to the 12-mile-wide subsurface lake that was reported in 2018, and what appear to be smaller patches of water, slush or wet soil in the same area.

“These results corroborate the initial discovery … of a stable body of liquid water in Ultimi Scopuli using a different and independent technique, highlighting at the same time a more extensive, complex scenario with ubiquitous water patches surrounding the subglacial lake,” the researchers wrote.

A 55-by-75-mile-wide map of radar readings shows potential reservoirs of subsurface water as bluish patches. (Pettinelli et al. / Univ. of Rome / Nature Astronomy)

However, they say trying to explain how water could exist deep beneath the ice in Mars’ polar region is “at best, a matter of speculation at this point in time.”

They speculate that the water may be heavily laced with perchlorates or other salts that would allow it to exist in liquid form far below the normal freezing point for pure water. Previous Mars missions have turned up evidence of such salts at the surface.

Experiments on Earth have shown that perchlorate brines could remain liquid in a super-cooled state at temperatures as low as 190 degrees below zero Fahrenheit (150 Kelvin).

The researchers say subsurface temperatures at Ultimi Scopuli could come close to that level, and they propose that metastable conditions at depth “are likely to produce a remarkable effect, both in terms of the formation of brines and in terms of their longevity on Mars.”

Perchlorate-laced water is toxic to most life on Earth. In fact, perchlorate is a key ingredient of some types of rocket fuel. Nevertheless, some particularly hardy microbes are able to make a meal out of it — and that might turn out to be the case on Mars as well.

“The possibility of extended hypersaline water bodies on Mars is particularly exciting because of the potential for the existence of microbial life,” the researchers write.

For that reason, they say bodies of water in Mars’ south polar region would “represent areas of potential astrobiological interest and planetary protection concern, and future missions to Mars should target this region.”

The only probe to send data back from a spot anywhere close to Mars’ poles was Phoenix Mars Lander, which detected what may have been splashes of liquid water in 2008 at its landing site in the north polar region. Scientists have talked up ambitious plans for polar expeditions on Mars for decades, but so far there’s been little follow-through.

Should there be? Or should more attention be devoted to other potential targets in the search for life elsewhere in the solar system, ranging from Venus to Europa and Enceladus?

In light of this month’s findings about the potential for life in Venus’ clouds, planetary scientist David Grinspoon is a bit meh about Mars.

“Mars??!!” he tweeted. “Life on Mars is so 2019.”

Mars’ spotlight brightens

It’s going to be hard to miss Mars in the weeks ahead: The Red Planet is getting brighter every night as it nears the closest point to Earth in its current orbit on Oct. 6, followed by opposition on Oct. 13.

Opposition is the time when Mars lines up directly opposite from the sun, as seen from Earth. This season is considered prime time for viewing Mars, which has started outshining Jupiter in the night sky. (Only Venus shines brighter in this month’s planetary parade.)

Mars gleams as a butterscotch-colored star in eastern skies after sunset — and at opposition, it should be right above you around midnight.

Mars is in opposition every 26 months, but some close encounters are closer than others. This time around, Mars will be only 38.6 million miles from Earth. The next time Mars comes this close will be in 2035.

In addition to Pettinelli, the authors of the Nature Astronomy study, “Multiple Subglacial Water Bodies Below the South Pole of Mars Unveiled by New MARSIS Data,” include Sebastian Emanuel Lauro, Graziella Capranelli, Luca Guallini, Angelo Pio Rossi, Elisabetta Mattei, Barbara Cosciotti, Andrea Cicchetti, Francesco Soldovieri, Marco Cartacci, Federico Di Paolo, Raffaella Noschese and Roberto Orosei.

By Alan Boyle

Mastermind of Cosmic Log, contributing editor at GeekWire, author of "The Case for Pluto: How a Little Planet Made a Big Difference," president of the Council for the Advancement of Science Writing. Check out "About Alan Boyle" for more fun facts.

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