Mars with ice cap

Mars has a significant amount of water locked up in ice. © ESA

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Liquid water found beneath the surface of Mars

Deep beneath the frozen ice cap at Mars's southern pole, scientists have discovered a lake of liquid water, raising the prospect that there are more subterranean lakes to be found below the surface. 

For the first time, scientists have been able to confirm that liquid water exists on Mars. Water is known to survive as ice on the red planet's surface and small amounts of water vapour have previously been detected, but the thin atmosphere prevents liquid water from forming on the surface.

But now researchers have found a lake of liquid water 1.5 kilometres below the ice of Mars's southern ice cap.

Tipped offs by blips

This latest study, published in Science, uses data collected by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS), a piece of equipment on the European Space Agency's Mars Express orbiter. Launched in 2003, MARSIS has been beaming down radio waves onto Mars, then recording their reflections from the surface.

It has been able to not only map the exterior of the planet, but also peer under the top layers of rock. After a few years the team based at the Italian National Institute for Astrophysics in Bologna noticed small, bright echoes being reflected back from under the planet's southern ice cap. 

Unsure what this might be, the researchers spent further years watching for these blips as the spacecraft passed over the south pole. Eventually, all the evidence suggested that this was not just underlying rock or subsurface ice, but was in fact a subglacial lake of liquid water.

ice cap on Mars

The southern pole of Mars is covered in thick glaciers. © NASA/JPL/Malin Space Science Systems 


Elena Pettinelli, MARSIS co-investigator, says 'These results indicate that we are probably in the presence of a subglacial lake similar to the lakes present beneath the Antarctic ice. Alternatively it could be a deep aquifer in which the liquid water fills the pores and fractures of the rock.'

The researchers can tell that the potential body of water is roughly 20 kilometres across, but are unable to say just how deep it might be. They know it must be at least a metre deep, otherwise the radar used to detect it would have simply passed straight through.

'We are not currently able to accurately estimate where the bottom of the lake or the base of the aquifer is located, but we can certainly say that it is at least a few meters in the order,' says Pettinelli.

A stable environment

This is not the first time that liquid water on Mars has been hinted at.

Previous images from orbiting satellites and samples taken by rovers have shown what appear to be ravines cutting through the surface. But is it thought that these may have been created by intermittent meltwater from the glaciers.

The most significant revelation in this latest discovery is the permanence of the lake.

For life to exist and then to survive, it needs a stable environment, unlikely to be provided by the seasonal flow of water on the planet's surface. So the presence of a larger and persistent body of water could change this.

This study could not determine whether there is (or has been) life living in this lake. What it does uncover is a useful starting point for any further missions.

Mars express spacecraft

Mars Express has been orbiting the red planet since 2003. © ESA


Could anything be living in the lake?

The conditions in the lake are expected to be extreme. To stay liquid beneath more than a kilometre of ice, it is likely that the water is hypersaline (very salty). Usually this would make it difficult for life to exist - but it's not beyond the realms of possibility.

Researchers looking at how life survives in extreme environments on Earth, such as the frozen poles, could help us understand how life might survive on Mars.

Dr Anne Jungblut, Researcher on Botanical Diversity, says, 'The study of the environments in the Antarctic and Arctic - which is what we do at the Museum - helps us to evaluate how life can survive under permanently low and freezing temperatures, with a lack of nutrients and in osmotic salt stress conditions, and provides insights to better understand the limits of life and habitability.'

In Antarctica, researchers have found subglacial lakes trapped beneath up to 800 metres of ice, isolated from the surface for tens of millions of years. Even there, the water is teeming with bacteria and archaea.

Dr David Williams, a Researcher of Diatoms at the Museum, says 'Yes, technically tiny life forms such as diatoms and cyanobacteria could survive in these environments. But that is not the question we should be asking.

'A more interesting question is whether we would know what we're looking at, even if we did find something in the lake. Would we even be able to identify it as life, if it originated on Mars itself?' 

Discover more about the search for life on Mars