Scientists have discovered what they believe is a lake hidden below a mile of ice at the south pole of Mars. The water was detected by radar and is situated below the southern polar ice cap of the red planet.

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The discovery was unveiled in a study conducted by the Italian Space Agency. The evidence comes from the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument (MARSIS) which is on the European Space Agency's Mars Express spacecraft.

The instrument uses pulses of radar to study the interior structure of the planet and has been orbiting Mars on the Mars Express European spacecraft since 2003.

The scientists explained that radar signals bounce back to the Mars Express in various different ways, depending on what material they have found — and according to the Italian team, the new signals picked up over Mars’ south pole could be explained only by a large underground mass of water.

“We discovered water on Mars,” said Roberto Orosei, a scientist at Italy’s National Institute for Astrophysics and the co-investigator on MARSIS, in a video about the discovery. Orosei said MARSIS “was able to detect echoes from beneath the southern polar cap of Mars that were stronger than surface echoes”.

“This condition on Earth happens only when you observe subglacial water like in Antarctica over places like Lake Vostok,” he added.

The team also suspects that while they have only found evidence for water at one location, it probably isn’t the only subglacial lake on Mars. The ‘lake’ is about 12.5 miles wide, at least 3 feet deep and is located under about a mile of ice.

Some scientists are not so certain about the discovery, however. Steve Clifford, a scientist who specializes in water on Mars at the Planetary Science Institute in Arizona, told Space.com that while the Italian team’s argument was “very persuasive” it is “not conclusive”.

Clifford said there was “always the possibility that conditions that we haven't foreseen exist at the base of the cap” that make it appear that there is water there.

The Italian scientists said that “bright subsurface reflections are evident within a well-defined, 20-kilometer-wide zone” that was surrounded by “much less reflective areas”. The bright area in question has a “high relative dielectric permittivity” which, in less scientific terms, means that it matches that of water-bearing materials.

“We interpret this feature as a stable body of liquid water on Mars,” the study said.