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Slope streaks signs of more water on Mars

Published: 11 September 2017

A step closer to answering the question about the presence of liquid water – and perhaps life – on current Mars has been taken. An article published in Scientific Reports written by the Atmospheric Science Group at Luleå University of Technology, points to the possibility that slope streaks, one of Mars’ characteristic features, are formed by transient liquid water.

– If there is a greater water activity on Mars that we thought before, the chances of finding life in some form in the subsurface are more likely, says Anshuman Bhardwaj, Associate Senior Lecturer of Atmospheric Science and first author of the article in Scientific Reports, an open access Nature magazine journal.

Slope streaks are found on the Martian surface. They are formed at low latitudes on terrains with low thermal inertia and high albedo and are covered by a relative abundant amount of fine dust. Until now, the most accepted explanation of the formation of the slope streaks resort to different kind of dry processes, for example dust avalanches, quakes or impact blasts.

As proposed by earlier research (read more here) there are perchlorates, a highly hygroscopic kind of chlorine salts, in the Martian regolith. As such, they have the ability to absorb water vapor from the atmosphere through a process known as deliquescence and form very concentrated solutions or brines at specific temperatures and relative humidity. This deliquescence process was found in one defined area, the Gale Crater, and it indicates that there is an exchange between soil and atmosphere and that the conditions in the Gale Crater are compatible with the formation of brines.

The deliquescence process is behind the design of the instrument HABIT that Luleå University of Technology is developing and that will be part of the ESA’s ExoMars 2020 mission.

– Theoretically it is possible that deliquescence can happen on Mars in other places than the Gale crater. We now try to establish that water activity is not a local phenomenon but found on a global level and that deliquescence is the root cause of slope streaks, says Anshuman Bhardwaj.

Water creating streak slopes

By analyzing images from two instruments, the Context Camera and the High-Resolution Imaging Science Experiment onboard NASA’s Mars Reconnaissance Orbiter, the researchers have been able to map the global distribution of slope streaks. With additional data on Mars’ geophysics and geochemistry they found a clear correlation between slope streaks and presence of chlorine salts, regolith hydration levels and atmospheric water content in the overlying boundary layer. So, where there are slope streaks, deliquescence can occur and brines can be formed due to the presence of favorable temperature and relative humidity conditions. Consequently brines can propagate through dust and create slope streaks.

 – Dust and gravity also play roles here. Dust is porous with high capillarity so the water can propagate through it. And the Martian gravity is weak, making the water run more easily, Anshuman Bhardwaj explains.

Great impact on future research

The new findings can have great impact on future exploration of Mars.

– If we establish that there is water all over the equatorial and sub equatorial areas of Mars, it will affect planetary protection policies.  Most likely harder requirements will be applied for the instruments landing there because of the risk of biological contamination. At the same time; if we assume that liquid water is required for any form of life on Mars, these regions are likely to host it and are therefore of astrobiological importance, says Anshuman Bhardwaj. 


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