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Image analysis methods are commonly employed to determine the size and shape of particles. Although commercial and noncommercial tools enable detection and measurement of grains from images, they do not provide good results in the case of images acquired during extensive in situ Martian investigations. Within the confines of the Mars Exploration Rover (MER) mission and the Mars Science Laboratory (MSL) mission thousands of images of sand grains were captured, and hitherto, they are the only source of ground-truth data on Martian sand particles. Therefore, a new approach is proposed to analyze such images. The semiautomatic algorithm allows fast detection and measurement of the size and shape of Martian grains from images obtained by the Microscopic Imager (MI) and the Mars Hand Lens Imager (MAHLI). The method was evaluated on 76 images of terrestrial and Martian deposits. The results for the terrestrial samples were compared to those from sieve analysis, as well as with ImageJ and Malvern Morphologi G3 systems. The method provides similar results to those from the other methods. It does not have any limitation on the size of grains, and permits separation of touching particles.

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Natural electromagnetic (EM) signals of extremely low frequencies (ELF, 3 Hz-3 kHz) can be used to study many of the electromagnetic processes and properties occurring in the Martian environment. Sources of these signals, related to electrical activity in the atmosphere, are very significant since they can influence radio wave propagation on the planet, the atmospheric composition, and the ionospheric structure. In addition, such EM signals can be employed in many purposes such as: surveying the subsurface of Mars or studying the impact of the space weather on the Martian ionosphere. As ELF waves propagate on very long distances, it is possible to explore properties of the entire planet using single-station recordings. In this study, we propose an experiment that allows measuring ELF signals from the Martian surface. Such measurements can be used for detection of electric discharges in the atmosphere and water reservoirs in the planetary subsurface.

<p>Granulometry, shape, and chemical composition analyses of the sediments studied by the Opportunity rover along its entire 45-km-long traverse have been used to classify sediments and provide information about their origin and depositional processes.</p><p>We have conducted granulometry and shape analyses of 179 sediment targets visible in MI images [1]. To facilitate the analyses, we have used the PADM algorithm - a semi-automatic tool for particle detection, measurement, and analysis [2]. This allowed identification of more than 70000 individual grains. For chemical composition analysis we used APXS data of 62 sediment targets [3]. The normative mineral composition was calculated from APXS according to the CIPW procedure to calculate the estimated density of the material and to classify in QAPF system.</p><p>The analyses show five deposit classes: i) dust with very fine sand enriched in sulphur, ii) fine basaltic sand, iii) coarse sand enriched in iron, found only on the plains, iv) gravel enriched in iron, also found on the plains, and iv) gravel with a typical for basalts amount of iron, found at the Endeavour crater rim. These classes occur in the following geomorphological settings: i) dust mixed with very fine sand is common on the leeward side of topographical obstacles, ii) fine sand is present in depressions, iii) coarse sand is related to coarse-grained ripples fields, iv) gravel occur as a lag deposit, especially in coarse-grained ripple troughs and at crater rims and outcrops.</p><p>The typical diameter of grains for the fine sand is 0.13 mm, and for the coarse sand - 1.20 mm. The best sorted coarse sands were found on the slopes and the crests of coarse-grained ripples. In most cases, the normative mineral composition of deposits fits in the basalt/andesite field of the QAPF classification. The coarse sand found in coarse-grained ripples was characterized by the highest content of iron and shows the most mafic composition in the QAPF diagram. This deviation from the basalt composition is related to iron-rich spherules (a frequent component of the gravel) than to a more mafic type of rock. On the other hand, the coarse sand grains found in ripple fields were characterized by lower roundness than the iron-rich spherules. Therefore, many of the transported by wind coarse sand grains had their origin in partial fragmentation of iron-rich spherules.</p><p>The work was funded by the Anthropocene Priority Research Area budget under the program "Excellence Initiative – Research University" at the Jagiellonian University.</p><p>[1] Herkenhoff, K. E. (2003) MER1 Microscopic Imager Science Calibrated Data Bundle. PDS Geosciences Node. DOI: 10.17189/1519006</p><p>[2] Kozakiewicz, J. (2018). Image Analysis Algorithm for Detection and Measurement of Martian Sand Grains. <em>Earth Science Informatics</em>, 11, 257-272. DOI: 10.1007/s12145-018-0333-y<em> </em></p><p>[3] Gellert, R. (2009). MER APXS Derived Oxide Data Bundle. PDS Geosciences (GEO) Node. DOI: 10.17189/1518973</p>