Liquid water has been found about a mile beneath Mars south polar ice cap. Some forms of microbial life are known to thrive in Earth's subglacial environments, but could underground pockets of salty, sediment-rich liquid water on Mars also provide a suitable habitat, either now or in the past?
Researchers have found evidence of an existing body of liquid water on Mars. InSight is also the first mission dedicated exclusively to learning more about the planet's interior in an attempt to glean clues about how rocky terrestrial planets like Earth formed during the birth of the solar system 4.5 billion years ago.
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. A subsurface radar profile is shown in the right hand panel for one of the Mars orbits.
"I really have no other explanation", said astrophysicist Roberto Orosei of Italy's National Institute of Astrophysics in Bologna and lead author of the study.
"The estimated temperature, which is to be debated to some degree, at the depth at which this water is occurring is said to be 205 K [90˚ F]", said Vlada Stamenković, a research scientist at NASA's Jet Propulsion Laboratory.
Based on that data, researchers believe Mars' southern polar ice cap features a liquid body of water hidden under ice, one likely filled with a type of brine containing things like salt and/or magnesium that enable it to remain a liquid at such cold temperatures.
"It is liquid, and it's salty, and it's in contact with rocks", according to Dr Enrico Flamini, the former chief scientist of the Italian Space Agency, who oversaw the research.
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Several researchers said it would be crucial to figure out whether this body of water is the only one, or part of an interconnecting body of underground aquifers - in part because a network increases the possibility it could have harbored life.
Stofan says finding liquid water is something scientists are extremely interested in scientifically, "because life here on Earth evolved in liquid water". Orbiters have also revealed huge glaciers residing just under the surface, potentially accessible to any future explorers or even colonists that go there in the future. Water is considered a fundamental ingredient for life.
But also, the more hard it is to, because laws of planetary protection state that we can not send any craft from Earth near a potential site of life for fear of contamination. Scientists working on NASA's Mars Reconnaissance Orbiter (MRO), which is equipped with a similar radar instrument called SHARAD, say that they simply do not get any readings for subsurface liquid in the region at all.
Mars might probably not be hospitable to life today, but when the planet was warm several millions of years ago, it might have hosted microbes - a theory scientists are struggling to confirm through various Martian missions that are now looking for evidence of past life.
The discovery is especially intriguing because underground lakes like this are also found near Earth's poles, particularly in Greenland and Antarctica.
Some experts are skeptical of the possibility since the lake is so cold and briny, and mixed with a heavy dose of dissolved Martian salts and minerals. It is about 20 km across, say the researchers in a release. The radar reflected the feature's brightness, signaling that it's water. On Earth those lakes are often connected by channels, forming branching riverlike networks of water that extend across vast spaces beneath the ice.