Liquid water on Mars – Expert reaction

Salty streaks identified by an orbiting spacecraft could be the first solid evidence of liquid water – a key ingredient for life as we know it – on the Red Planet.

Evidence of salty water flows on Mars have been identified by NASA’s Mars Reconnaissance Orbiter. The findings were published this morning in the journal Nature Geoscience.

Streaks on the surface on the planet have now been found to show evidence of hydrated salt minerals that come from water, while the surrounding area does not. The findings strongly suggest a link between the transient streaks on Martian slopes and the flow of liquid briny water.

Further press material is available on and on the NASA website.

The Science Media Centre collected the following expert commentary.

Prof Kathleen Campbell, Head of Discipline, Earth Sciences, School of Environment, University of Auckland, comments:

“While the presence of liquid water on Mars was predicted given the river gravels, carved canyons and ice found previously, it is by no means an easy feat to confirm in the present day, particularly from orbit where images are available at a higher resolution than compositional (spectral) data. Nor would liquid water be expected to hang around at the surface given the Red Planet’s cold temperatures, thin atmosphere and low atmospheric pressure.

“Using new methods, today’s results verify that particular locations and conditions – salty brines which seasonally wax and wane along gullied slopes – harbour water in liquid form, at least ephemerally.

“Because water is essential to life as we know it, the finding is important for extra-terrestrial habitability studies.

“The results compare favourably with Earth-analogue extreme environments of the ultra-dry Atacama Desert in Chile, where microbes living in salt crystals can survive on tiny amounts of water absorbed directly from the atmosphere.”

Prof Steve Pointing, Director, Institute for Applied Ecology New Zealand, AUT University, comments:

“This is the first proof that moving ‘liquids’ on Mars’ surface are made of water, albeit extremely salty brines.  These are likely to be ten times more salty than sea water here on Earth and so a human would actually receive burns from contact with these brines.

“However, extremely salty lakes that occur in many desert environments from California to Tibet do support simple microbial life that can tolerate this high salt content – and so this new study suggests this may be the sort of extant life we could expect on Mars.  These microbes often colour the water vivid pink due to a pigment they contain called bacteriorhodopsin, and I think that many scientists may now start considering this as a potential ‘biosignature’ molecule for life on Mars.

“The discovery of moving water on Mars would really add momentum to the search for life.  When water moves there is the opportunity for weathering of minerals and creation of nutrients to sustain life.  Any Martian life would also be able to use flowing brines to disperse and colonise new areas of Mars surface.

“There is however still a major problem that still faces any potential life in these brines and that is the inescapable radiation on Mars surface. Mars has high levels of ionising radiation because it only has a very thin atmosphere, unlike Earth’s thick atmosphere that shelters us and allows life to thrive.

“The only real option on Mars is for life to colonise beneath rock surfaces in what is known as the ‘microbial cabana’ strategy that was first proposed by myself and American colleagues to explain how microbes could colonise Mars.  Microbes can only do this in weathered rock, and flowing brines would certainly be a good weathering agent, so even if we do not discover little pink microbes in the brine itself, it adds to the possibility of finding other photosynthetic green microbes that form the microbial cabana in Mars-like environments on Earth such as the Dry Valleys of Antarctica.”

Dr Duncan Steel, New Zealand-based Space Scientist at NASA-Ames Research Center, Professor of Astrobiology at the University of Buckingham and Astronomer at Armagh Observatory, comments:

“Was the presence of liquid water expected? Yes!  In fact we’ve known for some time that liquid water exists on Mars. The major thing that has come about in the past two to three years is the recognition that there is a huge amount of ‘salts’ (in particular perchlorates) in the Martian soil/surface layers, and the fact that these dissolve in water and drop its freezing point significantly is a new recognition from the past  – several years. The present paper builds on this by explaining – to some extent – the ‘rivulets’ or lineae seen on Mars, mostly at the foot of cliffs. These have been a puzzle, because we had not expected so much liquid water as is evidenced by these active stream outlets.

“A proposed NASA mission in which I am involved, Icebreaker Life, for launch in 2020 would do just what its title says: break through the top layer of ice/permafrost, and see what is below.

“What do the current findings mean for our understanding of the potential for life on Mars? Liquid water is the sine qua non of life on Earth, and so we look for it elsewhere (on Mars; under the ice of Europa; erupting on Enceladus). Also, the perchlorates are strong oxidising agents, and so count against life, as such.

“There is much we must yet understand. There is certainly life in very salty environments on Earth, and studying extremophiles is a big thing. Indeed New Zealand has various extreme environments of great interest in this regard, for example hot sulphur springs.”

Further commentary from the Australian SMC:

Dr Alice Gorman, Lecturer in the Department of Archaeology, specialising in space archaeology, Flinders University, comments:

“People have pondered for a long time about our ethical obligations if life was found on Mars, and indeed the necessity of avoiding contamination from Earth is written into the Outer Space Treaty.  The discovery of these salty, seasonal flows on a planet we thought of as nearly dead dramatically increases the chances that it might support life. But to get close enough to the flows to sample them, we also risk introducing terrestrial micro-organisms. We know bacteria from Earth have made it into orbit on spacecraft. This discovery means that future Martian surface missions are going to have to adhere to an even higher standard than is already the case.”

Dr Alan Duffy, Research Fellow at the Centre for Astrophysics & Supercomputing, Swinburne University of Technology, comments:

“Off all the worlds we’ve explored, water flows only on the surface of one – ours. Which is why the discovery that water is now likely to be regularly flowing across Mars is so stunning.

“Dark streaks in the Martian soil appear to contain hydrated (ie water bearing) salts as seen by NASA’s satellite, the Mars Reconnaissance Orbiter. These strongly suggest that these seasonal features are linked to salt water after all.

“NASA is guided in its science by ‘following the water’ as where there’s liquid water there’s life. The brine on Mars might not directly support life but it suggests that the arid world isn’t as dry as once thought.

“We can’t tell if there’s life there yet but these dark streaks can tell us where to search in future.”