Lifting of Tribocharged Grains by Martian Winds

It is a long-standing open question whether electrification of wind-blown sand due to tribocharging—the generation of electric charges on the surface of sand grains by particle–particle collisions—could affect rates of sand transport occurrence on Mars substantially. While previous wind tunnel experiments and numerical simulations addressed how particle trajectories may be affected by external electric fields, the effect of sand electrification remains uncertain. Here we show, by means of wind tunnel simulations under air pressure of 20 mbar, that the presence of electric charges on the particle surface can reduce the minimal threshold wind shear velocity for the initiation of sand transport, u *ft, significantly. In our experiments, we considered different samples, a model system of glass beads as well as a Martian soil analog, and different scenarios of triboelectrification. Furthermore, we present a model to explain the values of u *ft obtained in the wind tunnel that is based on inhomogeneously distributed surface charges. Our results imply that particle transport that subsides, once the wind shear velocity has fallen below the threshold for sustained transport, can more easily be restarted on Mars than previously thought.

Soil fertility interactions with Sinorhizobium-legume symbiosis in a simulated Martian regolith; effects on nitrogen content and plant health

Due to increasing population growth and declining arable land on Earth, astroagriculture will be vital to terraform Martian regolith for settlement. Nodulating plants and their N-fixing symbionts may play a role in increasing Martian soil fertility. On Earth, clover (Melilotus officinalis) forms a symbiotic relationship with the N-fixing bacteria Sinorhizobium meliloti; clover has been previously grown in simulated regolith yet without bacterial inoculation. In this study, we inoculated clover with S. meliloti grown in potting soil and regolith to test the hypothesis that plants grown in regolith can form the same symbiotic associations as in soils and to determine if greater plant biomass occurs in the presence of S. meliloti regardless of growth media. We also examined soil NH4 concentrations to evaluate soil augmentation properties of nodulating plants and symbionts. Greater biomass occurred in inoculated compared to uninoculated groups; the inoculated average biomass in potting mix and regolith (2.23 and 0.29 g, respectively) was greater than the uninoculated group (0.11 and 0.01 g, respectively). However, no significant differences existed in NH4 composition between potting mix and regolith simulant. Linear regression analysis results showed that: i) symbiotic plant-bacteria relationships differed between regolith and potting mix, with plant biomass positively correlated to regolith-bacteria interactions; and, ii) NH4 production was limited to plant uptake yet the relationships in regolith and potting mix were similar. It is promising that plant-legume symbiosis is a possibility for Martian soil colonization.

Analysis of microbial lipids deposited on Mars Global Simulant (MGS-1) by geomatrix-assisted laser desorption/ionization-mass spectrometry

Lipids are among the organic substances that can work as biosignatures, indicating life in an environment. We present an experimental investigation concerning analysis of lipids from a microbial source deposited on the Mars Global Simulant (MGS-1) regolith by geomatrix-assisted laser desorption/ionization-mass spectrometry (GALDI-MS). Our results indicate that lipids from intact microbial cells of a black yeast strain can be detected in these mimetic samples of Martian soil. These lipid molecules are predominantly associated with the occurrence of adducts in the GALDI-MS spectra. The results can be helpful in the planning of future planetary missions.

Estimation of Water Content in Vera Rubin Ridge and Glen Torridon areas Based on Measurements of the MSL/DAN Instrument in Gale crater

<p>This work presents the latest results on the estimations of Water Equivalent Hydrogen (WEH) gathered in martian areas Vera Rubin ridge (VRR) and Glen Torridon (GT) by the Dynamic Albedo of Neutron (DAN) instrument installed onboard NASA’s Curiosity rover. The main science objective of DAN is to study bound water content in shallow layer of martian subsurface down to 0.6 m [1].</p><p>Extensive scientific campaign on Vera Rubin ridge was started in the middle of 2017 and lasted until the beginning of 2019 when the rover reached another region – Glen Torridon. VRR is mostly related to hematite minerals that might be formed in the presence of liquid water. On the other hand, GT region is thought to be associated with clay minerals, according to CRISM observations [2].</p><p>We will present the latest results on DAN passive observations in these Mars areas. Data are referred to the period of more than 3 years of observations or MSL traverse segment from 17 km to 23 km. The main result is the notable increase of WEH in GT in comparison with VRR, as well as in comparison with the whole Curiosity traverse. Possibly, the increase may indicate on the qualitative difference in neutron-absorption elements that are forming the soil of the GT region.</p><p>References:</p><p>[1] <em>Mitrofanov, I. G., et al., (2014). Water and chlorine content in the Martian soil along the first 1900 m of the Curiosity rover traverse as estimated by the DAN instrument. J. Geophys. Res., 119(7), 1579–1596. doi:10.1002/2013JE004553.</em></p><p>[2] <em>Murchie, S. L., et al. (2009), Compact Reconnaissance Imaging Spectrometer for Mars investigation and data set from the Mars Reconnaissance Orbiter's primary science phase, J. Geophys. Res., 114, E00D07, doi:10.1029/2009JE003344.</em></p>

Phosphorus interactions with Martian soil simulants

<p>Phosphorus (P) is an essential nutrient for plant growth. According to the vision of circular bioeconomy, the management of nutrient-rich wastewaters should include both treatment and utilization goals (Battista & Bolzonella, 2019). Consequently, the application of in-situ resources utilization (ISRU), using typical Martian soil (e.g., Yen et al., 2005), is vital for the sustainability of future long-term settlements on Mars.</p><p>Martian soil simulants, provided by The CLASS Exolith Lab from the University of Central Florida, were tested for their phosphorus sorption capacity. Sorption of phosphate anions (PO<sub>4</sub>-P) from aqueous solutions (AS) of KH<sub>2</sub>PO<sub>4</sub> and sodium bicarbonate, as well as from hydrolyzed human urine (HU) was examined at a preliminary stage, using three Martian soil simulants (MGS-1; Rocknest soil, MGS-1S; M-WIP Reference Case B and MGS-1C; M-WIP Reference Case C; Cannon et al. 2019). In particular, isothermal, kinetic, pH, temperature, initial sorbent concentration (5 g soil simulant/L AS or HU, 10 g/L and 15 g/L) and desorption experiments were carried out, the duration of which ranged from five days to three weeks.</p><p>The percentage of phosphorus removal was up to 60 % for the aqueous solutions and 24 % for the hydrolyzed human waste. The sulfate-rich simulant (MGS-1S) exhibited the best results. The major phases of MGS-1S are: gypsum, plagioclase, basaltic glass, pyroxene, and olivine. Temperature and the initial pH seem to be the dominant factors affecting P sorption. Equilibrium between sorbent and AS was achieved between five and seven days, as indicated by kinetic experiments. Isothermal experiments at 25 ⁰C with AS of different P concentrations displayed a linear correlation between adsorption capacity (q) and P-concentration (r<sup>2</sup>=0.98). Maximum q was observed at 8.5 and 27 mg/g for AS and HU experiments respectively, when 5 g/L of initial sorbent concentration was used. X-ray diffraction (XRD) of the sorbents treated with AS showed the presence of the newly formed phases berlinite and brushite. Perhaps due to hydrolysis of the pre-existing illite, aluminum bound with the solution’s phosphates, forming berlinite and buffering AS’s pH to lower values. Formation of brushite is possibly indicative of gypsum (predominant phase in the raw material) dissolution subsequently releasing sulfate anions. In a similar approach, XRD evaluation of the sorbents treated with HU revealed the newly formed phases calcite and hannayite. Phosphate and ammonia ions were likely to bind to the sample and were precipitated within newly formed calcium-bearing phases.</p><p>These experiments form a preliminary study of Martian soil simulants, and initial results indicate a possible use of Martian soils as waste recipients or as fertilizers in future missions.</p><p><strong>References</strong></p><p>Battista, F., & Bolzonella, D. (2019). Waste and Biomass Valorization, 10(12), 3701-3709.<br>Cannon, K. M., Britt, D. T., Smith, T. M., Fritsche, R. F., & Batcheldor, D. (2019). Icarus, 317, 470-478.<br>Yen, A. S., Gellert, R., Schröder, C., Morris, R. V., Bell, J. F., Knudson, A. T., ... & Blaney, D. (2005). Nature, 436(7047), 49-54.</p>

Semi-automated Image Segmenting Software for Martian Soil Granulometry

<p>Photoanalytical segmentation of individual soil grains and granulometry in high-resolution surface images are key in understanding sedimentation processes of planetary bodies before samples return to Earth. Here we present a Mathematica-based semi-automated image segmenting software tool that allows fast segmentation and granulometry analysis of Martian (soil) images based on the algorithm of Karunatillake et al. (2013, 2014), with a graphical user interface (GUI) to increase the software accessibility.</p><p>Our software has been adapted to Martian in-situ observation images including the Mars Hand Lens Imager (MAHLI) and Microscopic Imager (MI), providing segmenting and granulometry measurement through steps below: (1) Image imported: all common raster images are supported, as well as the IMG formatted MAHLI and MI images. While the MI image possesses a constant pixel size of 31 μm/pixel, for MAHLI images with various focal lengths, a focus motor count is required to calculate pixel size. The imported images are processed with gamma correction, contrast adjustment, background sharpen, and are visually decided whether there is a distinct foreground before going to the second step: (2) Image segmented: two independent modules are designed for segmenting the foreground and background with separate parameters, the coarser-grained foreground was masked before the finer-grained background is segmented. The GUI allows dynamic visualization of how the segmenting result changes with each parameter, facilitating the setting of parameters. (3) Granulometry: the grain size is calculated from the focal length and Wentworth classification of detected grains is established, highlighting the dominant class of grain size. The probability density and cumulative distribution of grain size can also be plotted. The granulometry results and parameters used are supported to export.</p><p>To check the performance of our software, we qualitatively tested our software with 57 MAHLI and MI images with or without foreground, with comparison to region based segmentation method such as BASEGRAIN, edge detection based method such as ENVI Classification tools and Feature Extraction tools, and supervised segmentation methods such as ENVI supervised classification tools and ImageJ Trainable Weka Segmentation tool. Our software shows better results in generating grains with closed boundaries and distinguishing adjacent grains with similar colors, with the fastest speed and less workload. Factors that may influence the accuracy of segmenting include image resolution, camera angle, inter-grain brightness/color contrast and shadow coverage.</p><p>In future work, a particle morphometry measuring function will be added so that statistics of grain roundness, sphericity, and angularity could be obtained. High-resolution images from the Moon and the asteroids will also be used in software testing to expand the range of its applicability to other planetary bodies. We will also consider its application on terrestrial cases, such as images of terrestrial sediments or petrological thin sections, which will need further improvement of the software concerning the increased compositional and optical complexity of terrestrial grains.</p><p> </p><p> </p>

Exploiting a perchlorate-tolerant desert cyanobacterium to support bacterial growth for in situ resource utilization on Mars

The presence of perchlorate in the Martian soil may limit in-situ resource utilization (ISRU) technologies to support human outposts. In order to exploit the desiccation, radiation-tolerant cyanobacterium Chroococcidopsis in Biological Life Support Systems based on ISRU, we investigated the perchlorate tolerance of Chroococcidopsis sp. CCMEE 029 and its derivative CCMEE 029 P-MRS. This strain was obtained from dried cells mixed with Martian regolith simulant and exposed to Mars-like conditions during the BIOMEX space experiment. After a 55-day exposure of up to 200 mM perchlorate ions, a tolerance threshold value of 100 mM perchlorate ions was identified for both Chroococcidopsis strains. After 40-day incubation, a Mars-relevant perchlorate concentration of 2.4 mM perchlorate ions, provided as a 60 and 40% mixture of Mg- and Ca-perchlorate, had no negative effect on the growth rate of the two strains. A proof-of-concept experiment was conducted using Chroococcidopsis lysate in ISRU technologies to feed a heterotrophic bacterium, i.e. an Escherichia coli strain capable of metabolizing sucrose. The sucrose content was fivefold increased in Chroococcidopsis cells through air-drying and the yielded lysate successfully supported the bacterial growth. This suggested that Chroococcidopsis is a suitable candidate for ISRU technologies to support heterotrophic BLSS components in a Mars-relevant perchlorate environment that would prove challenging to many other cyanobacteria, allowing a ‘live off the land’ approach on Mars.