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Talking water on Mars: Interview with Dr. Anna Losiak
Together with two colleagues, Dr. Anna Losiak, Institute of Geological Sciences, Polish Academy of Sciences, Wroclaw, published a science paper on ephemeral liquid water at the surface of the Martian North Polar Residual Cap.
The formation of large, young gypsum deposits within the Olympia Planum region, surrounding the North Polar Residual Cap (NPRC), has been an unsolved riddle since their discovery. This paper shows that gypsum might have been formed by precipitation from water formed below a thin layer of dust laying on glacial ice, heated by Sun irradiation.
OeWF: NASA has just confirmed evidence that liquid water flows on today’s Mars in a form of reccuring slope lineae (RSL). You published a scientific paper in August 2015, prior to NASA’s announcement.
Both groups started to work on this topic a few years ago; scientific research requires a lot of time. From their discovery in 2011 it was understood that the most probable explanation for the formation of RSL was, that they were created by liquid water flowing on the surface of Mars. However, despite of many attempts by many groups, no one was able to prove that this most probable explanation is actually the right one. So the publication by NASA is really cool because it shows for sure that there is liquid water on today’s Mars.
OeWF: Can I say that NASA’s confirmation is also a validation for your numerical model?
Not necessarily, no. RSLs and features that I study are located in very different regions of Mars. RSLs can be mostly found in the mid-latitudes and within Valles Marineris canyon. Our work is relevant to processes occurring on the glacial ice at the Martian Northern polar cap, and possibly also at the Southern polar caps.
Also the processes of liquid water formation in those two cases seem to be very different. We still don’t know how exactly RLS are formed but the most probable explanation right now is, that some of the salts that are present within the soil are hygroscopic, which means that they are sucking up the moisture from the air. Once they get enough water the entire surface can start flowing.
What we are proposing in our paper is that the Sun is warming up dust grains that are locally laying on the surface of glacial ice, which in turn can cause glacial ice to melt.
OeWF: Please explain us the key conditions at the surface of the Martian NPRC which are the basis for your calculations.
First of all, this process is not happening every day – for most of the time, the Martian polar cap remains deeply frozen. However, during the warmest days of the summer the solar irradiation may provide enough energy to the dust to warm it sufficiently to melt pure water–ice located below a layer of dark dust particles. Second of all, this process can happen only on the equatorial-facing slopes of the deep troughs incised within polar cap, where dusty glacial ice is exposed. And finally, dust needs to be quite dark and densely packed in order for it to heat up sufficiently. However, overall, melting occurs over a wide range of parameter values which shows that this phenomenon is relatively common (albeit localized).
Once formed by melting, liquid water may persist for an amount of time potentially sufficient to partially dissolve dust grains and form other minerals such as gypsum. A similar situation occurs in the case of Antarctic meteorites. Liquid water can be metastable at the NPRC because the pressure during the summer season is approx. 760–650 Pa which is above the triple point of water. (The triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.)
OeWF: What are the results of your model?
Our results shows that melting of water below layers of dark dust grains could provide sufficient amounts of water for the formation of evaporites. This process is similar to that observed for basaltic meteorites found on the surface of the Antarctic ice sheet. Dust grains are deposited on the surface of Martian NPRC by aeolian processes (especially during dust storms). If the deposited layer of dust is quickly covered by fresh snow, dust weathering is restricted, as is inferred from studies of dust bands in Antarctic ice. As a result dust-rich layers within the ice often form distinctive bands visible in orbital imagery. Dusty ice is exposed in equator-facing slopes of the Mars’ spiral troughs by katabatic wind erosion. On the steepest parts of the spiral troughs, a layer of dark dust-sized grains exposed at the surface is radiantly heated which melts the ice beneath, as shown by our study. Some of this water vaporizes due to low atmospheric pressure, but some of it is preserved under the layer of dust particles or ice as long as the temperature of the dust is above the melting point of water. This water reacts with the dust grain, dissolving species adhering to the grain and forming secondary minerals including evaporates like gypsum attached to the weathered dust grain.
OeWF: What do you think will be a consequence of your results and NASA’s study for the exploration of Mars?
I think that the discovery of liquid water on Mars got a lot of attention, which may encourage politicians to spend more money on planetary science. From the scientific point of view, the discovery of liquid water on Mars shows that if life ever appeared on Mars, it can still be there. Right now we know at least two good places to look for currently living Martian organisms.
If I was a Martian organism, and I could choose between those two locations, I would prefer to live on the north polar cap. The water is much less salty there and warm conditions are repeating themselves quite regularly. So probably every summer there is at least one day when there is liquid water. One day every year does not seem like much, but flowers on Earth deserts sometimes need to wait for tens or hundreds of years before they can all bloom after a very rarely occurring rain. It is possible that also on the Martian NPRC something similar is taking place.
OeWF: Would you like to fly to Mars to study the geologic realities?
Of course. That’s the aim of almost all planetary scientists! I really hope that I will not be too old before there will be a selection of astronauts for a flight to Mars.
Robotic exploration is very useful and much cheaper than human missions. However, the problem with using only robots is that we will never be sure, that organism-like features found by a rover are really life or rather an equipment error, or some unexpected abiotic reaction. So, the only way to really prove that there is life on Mars is to either bring some samples to Earth or to bring scientists and laboratories to the Red Planet. This is why we need people on Mars!
OeWF: Thank you so much for your time.
The interview was conducted by Marlen Raab, OeWF editorial team
This article is available in: German
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