Have you discovered an underground lake on Mars?

The water is abundant on the satellites of the outer solar system, but until now, it had been incredibly difficult to find large quantities on Mars.

Radar scans carried out on the red planet suggest the presence of a natural saltwater reservoir that extends for about 19 kilometers and is about a mile and a half deep from the surface at the south pole of Mars. In addition, it is likely that there is not a single underground lake.

"There are other areas with favorable conditions for the presence of water, and so it is possible that the one identified is not the only lake," says Elena Pettinelli, director of the laboratory of Physics applied to the Earth and the Planets of Roma Tre University. the authors of the study published recently in Science [un articolo firmato da Roberto Orosei, dell’Istituto Nazionale di Astrofisica (INAF); Il gruppo di ricerca ha coinvolto oltre a INAF e Roma Tre, anche l’Università di Roma “Sapienza”, l’Università “Gabriele d’Annunzio” di Pescara, e Istituti del Consiglio Nazionale delle Ricerche e Agenzia spaziale Italiana].

If its presence is confirmed, the groundwater reserve could help clarify some issues, for example, what happened to the ancient oceans present on Mars, as well as provide a resource for future human settlements. And, even more exciting for exobiologists, these conditions could be an ideal habitat for extraterrestrial life forms.

"In similar environments on Earth in Antarctica, the presence of bacteria has been detected even in the depths of the ice," says Pettinelli.

The Ancient Oceans of Mars

Billions of years ago, Mars was probably a warm planet covered with sea, just like the Earth. But today, it looks like a dry and toxic desert, and for decades scientists have been trying to understand what has happened to the oceans that once bathed the planet.

In the past, scientists found traces of water on Mars, but generally it was only temporary or almost inaccessible, or suspended in the atmosphere, or trapped in permafrost or in the polar ice caps; or he ran on the crater slopes only in a few seasons. And the amount of water found is certainly not the same as the one that once formed the ancient seas on Mars, and would not even be enough to start any agricultural activity on the planet.

"We know that once there was a lot of water on the surface of Mars, and today it is no longer present in the same amounts," says Bobby Braun from the University of Colorado at Boulder. The scientists then speculated that some of the missing water could be trapped. in underground aquifers containing large reserves of liquid.

In Search of Water

However, human beings, until the beginning of this millennium, have not been able to launch spacecraft capable of detect the presence of groundwater.

One of them, the Mars Express space spacecraft of the European Space Agency, revolves around Mars since 2003; on board there is an instrument called MARSIS, which uses radar pulses to scour the Martian subsoil. It works by sending low frequency radio waves into the planet, which enter the ground to bounce off boundaries and geological structures. By studying how these waves are reflected in the spacecraft, scientists can infer what could be found in the basement.

In 2008, the team of researchers involved in the MARSIS study was able to glimpse what could be very bright reflections near the South Pole of the planet, in an area where ice caps are piled up on each other. . On Earth, the brightest radar reflectors are brackish water ponds, and the research team has decided to take a closer look at the region.

After a few years collecting data that did not prove to be very useful, the team finally began in 2012 to gather enough observations to compose a broader and more meaningful picture of the situation. . It then took another three years and 29 space probes before the scientists had enough information for a complete treatment.

"We knew there was something out there, and we were curious, we wanted to know what was under that area," recalls Pettinelli. "And we were stubborn enough to proceed with the badysis of the data."

The organization of the MARSIS data was not easy, and over the next two years, it was not easy. Research team compiled and processed the relevant observations and worked very hard. to rule out alternative possibilities, such as the one that could involve deeper layers of frozen carbon dioxide.

Finally, comparing the reflectance models on Mars with those observed on Earth, scientists were convinced that they had discovered a subglacial lake. The researchers hypothesized that the lake contains – probably several meters deep. – various salts that help make it liquid even at extremely cold temperatures.

A lake on the red planet?

Thanks to the data collected with the Mars Express probe, the research team will be able to compare the results of the discovery with the characteristics of the lake lakes, sometimes very large, located under the Greenland ice sheets. of Antarctica, able to house life forms.

But not everyone is convinced that the water reserve is really a lake. The same research group claims that this could be an accumulation of moistened debris, more like muddy sediment than a full tank of water. To determine the exact nature of this structure, a different instrument will be needed, says Pettinelli.

"We do not have enough information to say for sure whether it's a lake or a saturated sediment like an aquifer", explains Pettinelli. "However, it would be more interesting if it was a lake".

But there is currently another radar in the orbit of Mars, which adds interesting information.

"We do not see anything that is reflective," says Bruce Campbell of the Smithsonian Institute's National Air and Space Museum in Washington, a member of the SHARAD radar team mounted at edge of NASA's Mars Reconnaissance Orbiter spacecraft.

The Mars Reconnaissance Orbiter radar, orbiting Mars since 2006, aims to observe large areas of the Red Planet's landscape, including many areas located on the South Pole's stratified deposits, and until now has nothing identified similar to a water reserve.

This is probably due to the fact that the MRO radar uses different wavelengths that are scattered due to the presence of polar ice, before it can reach the potential reservoir located deep down, says Jack Holt of the # 39; university. Arizona. But – he adds – the SHARAD radar should be able to detect anything that is reflective, such as the water of a lake.

"Salt water is probably the most powerful radar reflector in the world, in addition to metal," he says. "The presence of a lake implies a crystal clear reflection, such as that of a mirror, which is therefore more likely to be detected by SHARAD. More difficult, however, for the radar to locate saturated sediments. , characterized by a rougher surface ".

Scientists, including those who are part of the team of researchers who studied MARSIS radar data, on the Mars Express probe, can not wait to confirm the discovery. "We have a lot of convincing evidence to support the fact that it is water, and we hope that other data acquired in the future can confirm our hypothesis", continues Pettinelli.

The mystery of the oceans has disappeared

the presence of the salt water reserve could help to solve the mystery of the disappearance of the ancient oceans on Mars and provide clues to the hydrological cycle of the planet, supposed to involve underground aquifers that contribute to melting polar ice caps. Nathalie Cabrol, of the SETI Institute, explains that water flows northward from the southern uplands.

"At the North and South Pole of Mars, there could be very wet sediments or water," he says. "It is in these places that we expect that there is a water reserve".

The work of Cabrol, an exobiologist, also includes the study of environments similar to Mars, which sometimes require diving into lakes hidden between the Andean peaks. According to the researcher, the discovery is electrifying, whether it is wet sediment or a real lake.

"What is observed is the potential presence of water, a reservoir, and it is possible to produce nutrients from minerals," he says. "For this to happen, we need a source of energy, and if in the past the polar regions of the planet were home to ancient active volcanoes, that is without a doubt a perfect place to accommodate life forms ".
On the other hand, he observes, "it would be problematic to go to a similar place because it would be among the special areas covered by global protection," he explains in reference to United Nations standards to prevent interplanetary contamination of habitable environments.

This new water supply could be useful to humans who someday, perhaps, will move to Mars.

"I think it's really unlikely that the first humans on Mars will drill several miles deep," says Braun, consultant for the National Geographic television series "Mars," and former head of the company. NASA technology industry. ]
"But I also think that it is likely that if the discovered site was actually a lake, there would be other water accumulations perhaps closer to the surface", continues Braun. "Of course, when you move to a place, you plan a base camp, it is important to know if there is a large body of water a few dozen meters deep."