The surface of Mars

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There's a lake on Mars, it's been revealed today.

Almost 4.5 billion years ago, Mars had six and a half times as much water as it does now and a thicker atmosphere. It's similar to other ground-penetrating radars used here on Earth to explore beneath the ice sheets of Greenland and Antarctica.

The lake was found with a radar instrument called Marsis on board the European Space Agency's Mars Express orbiter which arrived at March in 2003.

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MARSIS "then measures how the radio waves propagate and reflect back to the spacecraft", said the study. And in recent years, scientists actually drilled deep beneath the Antarctic ice into one of these, the subglacial Lake Whillans, which had been cut off from the surface for millions of years. Liquid water may be largely absent on the surface, but a stunning new analysis from the European Space Agency (ESA) says there's plenty of it in a vast underground lake near the planet's south pole. The researchers doubted the signal was real, however, because it appeared in some orbital passes but not others. And while that would require "technological developments that at the moment are not available", the study's lead author, Dr Roberto Orosei of the National Institute for Astrophysics, said the researchers nonetheless have high confidence in their results.

To bypass this problem, the team commandeered a memory chip on Mars Express to store raw data during short passes over intriguing areas.

The scientists analyzed radar profiles, within a 200 km-wide area, collected between May 2012 and December 2015.

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The lake stretches about 20 kilometers across and lies beneath the South Pole. Another clue comes from the permittivity of the reflecting material: its ability to store energy in an electric field. For MARSIS to be able to detect such a patch of water, it would need to be at least several tens of centimeters thick. Such a hot spot could, in fact, be responsible for the MARSIS team's newfound lake.

"The presence of a body of liquid water beneath Mars's south polar cap has various implications, opening new possibilities for the existence of microorganisms in the Martian environment", says Sebastian Lauro, a study co-author based at Roma Tre University in Rome. "This is something that is to us the tell tale sign of the presence of water", says Prof Orosei. "A lake, not some kind of meltwater filling some space between rock and ice, as happens in certain glaciers on Earth", Prof Orosei said. Scientists in the past have discovered ice on the planet, pointing to the logical conclusion that life could, if not did, exist there. But that's not enough to overcome the extremely low pressures of the Martian atmosphere, which would cause any ice to sublimate off into vapor instead of melting. But Clifford holds out hope subsurface geothermal hotspots like those that power volcanoes and hot springs on Earth could sufficiently heat portions of the Martian underworld to allow liquid reservoirs to exist there without the need for life-sabotaging salt levels.

Since 1964, the United States has launched more than 20 robotic spacecraft to the red planet at a cost of more than $20 billion in an evolving campaign to map out the red planet's surface, determine the role of water in its history and to search for signs of past habitability and the organic building blocks of life, Harwood reported.

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