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Evidence of salty water flows on Mars have been identified by NASA’s Mars Reconnaissance Orbiter. The researchers have examined unusual streaks found on the surface of Mars that change with the seasons – called recurring slope lineae. These streaks have now been found to show evidence of hydrated salt minerals that precipitate 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 brines.
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Professor Geraint Lewis is Professor of Astrophysics & ARC Future Fellow at the Sydney Institute for Astronomy and Associate Head for Research in the School of Physics, The University of Sydney.
“Mars appears to be a cold, dry planet, but observations over the years have revealed streaks on the surface that come and go with the seasons. In this new paper, Ojha have uncovered the signature for salts in the streaks, critical evidence for the streaks having formed by flowing, or at least dribbling, water.
As salt on your frozen driveway lowers the freezing point of ice, this briney remains liquid in the harsh conditions on Mars, allowing it to flow across the surface in the chill of a mid-summer on Mars. Many question remain, including what is the source of this briney water, be it locked up ice under the surface, or rarified vapours in the atmosphere, but this new result bolsters the argument for water on the surface of our planetary companion.”
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Dr Alan Duffy is a Research Fellow at the Centre for Astrophysics & Supercomputing at Swinburne University of Technology
“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.”
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Dr Amanda Bauer is a Research Astronomer and Outreach Officer at the Australian Astronomical Observatory
I can simply say that the potential presence of liquid water on the surface of Mars is incredibly exciting because water is essential for life as we know it to exist. More work is needed to understand how exactly these seasonal salty water streams are formed on Mars, but the new evidence for water flow is certainly an exciting step forward in understanding water activity on Mars.
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Dr Eriita Jones is a postdoctoral researcher at the University of South Australia
“An observation of salty liquid water flowing across the Martian surface is extremely significant. Liquid water is not stable on the Martian surface in the present day, due to the low atmospheric pressure and cold temperatures. Water ice is the dominant phase of water observed on Mars, but even this is restricted to near polar latitudes where the surface temperatures are cold. The regolith at low latitudes is thought to be predominantly dry and inhospitable to life. Some scientists have challenged this view however, proposing that salts in the Martian soil could allow sufficient volumes of liquid water to accumulate in the shallow soil.
Salts can ‘absorb’ water vapour from the Martian atmosphere during high humidity, or can cause melting if in contact with water ice. Salts lower the freezing point of water, allowing salty water to remain a liquid at temperatures below zero.
This new evidence suggests that in fact these processes are allowing liquid water to accumulate tens of cm beneath the Martian surface, and to eventually grow to sufficient volumes that it leaks out and flows downslope. This has significant implications for the ability of the Martian regolith to support life, as liquid water is a necessary ingredient for all life on Earth. The new results may indicate that currently the low latitudes of Mars may have subsurface water environments that would be habitable to microbial life.”
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Dr Alice Gorman is a lecturer in the Department of Archaeology, specialising in space archaeology, at Flinders University
“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.”
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Dr Jonathan Clarke is President of Mars Society Australia
“This announcement is further confirmation of what has been suspected for some time, that ongoing interaction between Martian surface materials and water in the atmosphere play an important role in the surface processes of the planet.
As pointed out by the authors, seasonal release of water to form dark streaks on steep slopes, the recurring slope lineae, perhaps by salts through a process called deliquescence, or by melting of seasonal ice, provides potential habitats for microbes. This makes these areas an important target for any future mission to search for life on Mars. The confirmation of the presence of perchlorate salts suggests that deliquescence may be more likely. We already know from other missions that the perchlorates are widespread on Mars, this may mean that potential habitable micro-environments are also widespread.
Possible liquid droplets forming round salty soil particles were seen on the legs of the Phoenix spacecraft during its mission to the Martian Arctic in 2008, at the site where perchlorate salts were first deposited. As well as being a potential habitat for Martian life, such water-rich salts could, with appropriate planetary protection, also serve as a water source for human-crewed expeditions to the Martian surface.”
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*Spectral evidence for hydrated salts in recurring slope lineae on Mars, Ojha et al., Nature Geoscience, 2015, doi: 10.1038/NGEO2546