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Active Surface Processes On Mars: A Laboratory, Field And Remote Sensing Study

Periodic Reporting for period 1 - ACTIVE_MARS (Active Surface Processes On Mars: A Laboratory, Field And Remote Sensing Study)

Reporting period: 2016-03-01 to 2018-02-28

The goal of this project was to analyze ongoing geological activity across the whole of Mars. The project was firstly focused on in situ measurements of terrestrial dust devils (small whirlwinds entrained with dust and sand) and their implications to Mars (Figs. 1, 2). On Mars, dust devils are the most widespread annual activity. They erode and transport dust and sand and it is thought that they contribute up to 50% of the material of the global dust content in the atmosphere. During this project we got new insights into the internal structure of dust devils. Furthermore, we measured directly pressure drops triggered by dust devils, as well as their vertical and horizontal wind speeds. These results can be directly compared to meteorological datasets acquired from landers on Mars to estimate the dimensions, strengths, and the general appearance of dust devils. This will be important for future Mars missions because dust devils could be harmless and even helpful (cleaning of landers by blowing away deposited dust on solar panels), but also harmful because they can transport particles into the smallest gaps of instruments on Mars and they have also an influence on the local climate and weather. Up to date knowledge about terrestrial and martian dust devils is limited, but as seen above, it is worth knowing more them.
The second focus of the proposal was to analyze current mass wasting features on the surface of Mars. The widely accepted knowledge is that water is a very unlikely medium to transport large volumes of sediment because of the limited amount of liquid water available on the martian surface. But with our unique experiments performed in the Mars Environment Chamber (Figs. 3, 4), we have found evidence against this paradigm because we have observed a new transport mechanism triggered by liquid water under low pressure which is not possible on Earth. Liquid water transportation of sediment down a slope on Mars could be possible, even with low amounts of water because water will boil at very low surface temperatures (slightly above zero). That means that less water is needed to transport material on Mars. Our findings are important for the discovery of triggering mechanisms for currently-observed martian mass wasting features, as well as to identify possible liquid water reservoirs and their volume estimations on Mars. For future (manned) missions to Mars it is vital to know where we can find water at the near surface and how much of it is available. Our results are one step further for the understanding of the complex behavior of liquids on this planet.
Part I was about in-situ vertical grain size distributions of two dust devils sampled during a field campaign in the northern part of Morocco in 2012. The samples were analyzed in 2013 and 2014. During the project, the publication was written and submitted.
Main results are:
- The majority of all lifted particles were only lifted within the first meter. Nearly all sand grains occurred in the first meter which is the first directly measured evidence of the occurrence of the “sand skirt” of dust devils.
- Between ~60% to ~70% of all lifted particles were small enough to go into and stay in suspension, so these data will have an influence on studies of climate, weather, biogeochemistry, and (on Earth) human health.
- We get better information of the internal structure of dust devils and our sampled dust devils show comparable internal particle load structures despite the fact that they have different dimensions and intensities.

These results were presented in a peer-reviewed publication in the journal “Astrobiology” (J. Raack et al. (2017) Astrobiology 17) and at several scientific conferences.

Part II included two different field campaigns. The first field campaign was in 2016 to the desert in the northeast of Morocco. In-situ samples of six different dust devils were taken (Figs. 1, 2) and numerous dust devils were investigated with different meteorological instruments such as atmospheric pressure, vertical and horizontal wind speed, temperature, etc. During the second field campaign, in 2017 to a desert in Nevada, we made the same measurements of dust devils to compare these with measurements from Morocco.
Main (preliminary) results are:
- We measured in-situ pressure drop magnitudes and vertical wind speeds of dust devils in Morocco and Nevada. Plotting peak pressure drop magnitudes (P) versus peak vertical wind speeds shows that the vertical wind speed is about 0.06×ΔP. With this it could be possible to calculate wind speeds of dust devils only with the knowledge of the pressure drop (which is often the only measurement on Mars).
- Furthermore, we plotted the vertical winds speed versus the tangential wind speeds which shows that the vertical wind speed is about half the tangential wind speed. This is in good agreement with other studies.

To date, preliminary results were presented at international scientific conferences.

Part III consisted of laboratory experiments with the Mars Environmental Chamber (Figs. 3, 4). We investigated the behavior of liquid water flows over sandy surfaces at low pressures (~7-9 mbar, comparable to pressures on Mars) with different sediment and water temperatures (Fig. 6), as well as different slope angles and flow rates (unpublished). To date, two peer-reviewed publications (one in the high profile journal Nature Communications) were published.
Main results of the first laboratory campaign are:
- When the surface temperature is high enough (in this case ~15° C) “levitation” of saturated sediment pellets took place. The pellets levitate on a cushion of vapor released by boiling, comparable to the Leidenfrost effect (e.g. water drops “dancing” around on hot cooking plates). This was the first time that these observations were made.
- The effect of levitation with subsequent other transport mechanisms caused a higher transport capacity of the flow. This means that nine times more sediment was transported when the surface temperature was slightly higher (Figs. 7, 8).
- The experiments show that the amount of needed water to move comparable sediment amounts was an order of magnitude lower for warmer surfaces. This means that less water is used on Mars to transport material.
- Numerical scaling to the martian gravity imply that levitation could persist up to ~48 times longer on Mars, which will lead to an enhanced transport capacity.

To date, results were published in two peer-reviewed publications (J. Raack et al. (2017) Nature Communications 8, 1151 and C. Herny et al. (2018) GSL, Special Publications 467) and at scientific conferences.
Results of the laboratory experiments had and still have a huge because if some specific parameters occur, liquid transportation of sediment on Mars could be “easier” than previously thought. It is widely accepted that liquid water could not be the triggering mechanism for observed recent and present-day mass wasting features on Mars, because too much water has to be used, which is normally not available. With our experiments, we have shown that this could be wrong. It means that in the low pressure environment of Mars less water is needed to transport material downslope. The laboratory experiments will not resolve the still unknown mechanisms for the formation and modification of recent and present-day active mass wasting features, but it gives hints and new ideas how to solve this problem in the future.