<p><strong>Introduction:</strong> This abstract deals with analysing the interaction between the ExoMars lander and the surface deformation at the touchdown in the Oxia Planum region of Mars. The analysis of ExoMars landing has been conducted by IRSPS under Thales Alenia Space Italia and ESA by means of computer simulations and physical test with a lander mock-up. The mission involves landing via retro-rockets to slow down the lander before impact. Despite the deceleration, the impact will transfer significant energies to the ground, exceeding those experienced in past missions.</p> <p><strong>Landing dynamics: </strong>Several variables of the descent phase influence the impact dynamics, such as the linear and the rotational terminal speeds, the inclination along the three axes, and the mass. We employed multi-body physics simulations to translate these input parameters into touchdown dynamics and ground stresses. The parameters and topographic data have been used in Unity and MATLAB environments to simulate the impacts. According to the Engineering Constraint of the mission [1], the topography has been modelled with slope values up to 20&#176;.</p> <p><strong>Geotechnical parameters:</strong>&#160; Estimating the geotechnical characteristics of Martian soil remains a rather complex challenge. After detailed mapping of the landing ellipse and a careful identification of the surface lithologies, we simulated different lithotypes: &#8220;Regolith&#8221; (poorly-sorted sand to cobble, loose, non-lithified material), &#8220;Mudstone&#8221; (silty marl and lithified clays with low calcite content), &#8220;Sandstone&#8221; (sandstones from deltaic and fluvial environments), &#8220;Halite&#8221; (evaporites from lacustrine/flood plain and deltaic interchannels), &#8220;Tuff&#8221; (pyroclastic material) and &#8220;Basalt&#8221; (lava flows). The geotechnical parameters have been extracted from terrestrial analogues and simulants and summarised in Table 1.</p> <p><img src="" alt="" width="1062" height="577" /></p> <p><strong>Geomechanical simulations:</strong> The numerical modelling of the stressed terrain has been performed with the Itasca FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) software. One hundred and eighteen different simulations have been performed, tuning the landing variables concerning the impact dynamics, the geotechnical parameters, and the topography. The input conditions of the individual tests were composed through the programming languages FLAC3D-embedded FISH and Python. Apart from &#8220;Regolith cases&#8221;, the simulations resulted in minimal and negligible displacement (below 1 mm), although it does not exclude minimal surface fracturing of the rock. The results indicate that in none of the cases did the pressures reach the bearing capacity of the lithotypes, remaining in the domain of elastic deformations. In &#8220;Regolith&#8221; cases, due to the lower capacity, the excavation of the pads reached a range of values up to 10 cm with low terrain slopes (Fig.1) and up to 20-25 cm at higher inclinations. The cases where the first impact occurs on a single pad showed the highest displacement rates, especially when the Landing Platform is inclined perpendicularly to the ground. Subsequent contacts with other pads resulted in lower displacements due to energy dissipation and impact geometry.</p> <p><img src="" alt="" width="1063" height="746" /></p> <p><strong>Field test campaign:</strong>&#160; To validate the adopted methodology and get more details about the impact dynamics, a field tests campaign has been performed with a full-size mock-up of the Landing Platform. The mock-up structure replicates the same shape and physical dimensions of the real L.P. but with a mass scaled from the original to compensate for the difference in gravity (Fig.2). It is equipped with an onboard triaxial IMU, capable of recording system speed and attitude during impact. The launching system, designed to reach desired velocities and address the touchdown conditions, consists of an inclined rail of steel girders and a quick release system. As an analogue of the regolith terrain material, we used the argillitic sub-unit of the &#8220;Argille Varicolori&#8221; formation, outcropping in southern Abruzzo and Molise regions in Italy. Geotechnical laboratory tests on terrain samples confirmed that the material is a good compromise between regolith and the clay-bearing lithology observed in the landing area. The material used has been prepared and left to dry in a quarry specialised in handling such material. Surface deformation has been measured with sub-centimetric accuracy through laser scanner point clouds realised before and after the tests (Fig.3). Eight different field test scenarios have been performed and subsequently replicated in FLAC3D for comparison. The test configurations were chosen to be representative of the variability of previous geotechnical simulations. The comparison, summarised in Table 2, displays a mean percentage difference of -0.8% (standard deviation of 8.5%), reaching a maximum of -15%. Deformation rates are also compliant with the ranges observed on Mars simulations, up to 10 cm in flat terrain conditions and up to 17 cm at 20&#176; of the slope.</p> <p><img src="" alt="" width="1061" height="601" /></p> <p><img src="" alt="" width="1081" height="1013" /></p> <p><img src="" alt="" width="1076" height="439" /></p> <p><strong>Conclusions:</strong> Surface deformation characterization studies have required the application of several simulations due to the wide variability of the physical, geological, and topographical factors involved. The field test campaign validated the methodology&#8217;s reliability and confirmed the expected deformation rates. The test results show that with significant thicknesses of regolith, the impact can lead to soil deformation rates ranging from five to more than twenty centimetres. Analyses of other lithotypes indicate more favourable results with negligible deformations due to not reaching the load bearing capacity. In both cases, the displacements should not reach values that compromise the onboard instrumentation, supporting landing safety in different surface conditions with a slope up to 20&#176;.</p> <p><strong>References:</strong> [1] ESA (2013). ExoMars 2018 LSS UM Ref: EXM-SCI-LSS-ESA/IKI-003, Issue: 1.0, 17 Dec. 2013</p> <p>&#160;</p>
<p><strong>Introduction</strong></p> <p>Studying planetary field analog environments is a key point in order to define the physical and chemical parameters that favor life on Earth and other planets. Terrestrial hydrothermal springs have long been considered among the most significant planetary analogs searching for traces of life on Mars [1].</p> <p>Hyperspectral data have been recognised to be more suitable for the detailed mapping and identification of rocks and minerals identification of land surface, especially for minerals [2].</p> <p>Notwithstanding the technological advances, hyperspectral satellites are still poorly represented in spaceborne missions for Earth Exploration compared to multispectral ones. In this context, the Italian Space Agency (ASI) EO mission named PRISMA (PRecursore IperSpettrale della Missione Applicativa, [3]) offers a great opportunity to improve the knowledge about the scientific applications of spaceborne hyperspectral data.</p> <p>PRISMA, launched in March 2019, includes a panchromatic and a hyperspectral camera with 239 spectral bands. Specifically, the PRISMA satellite comprises a high-spectral resolution Visible Near InfraRed (VNIR) and Short-Wave InfraRed (SWIR) imaging spectrometer, ranging 400-2500 nm, with 30 m ground sampling distance (GSD) and 5 m GSD for the panchromatic camera [4].</p> <p>Our analysis with PRISMA images was mainly performed on an arid environment in a remote region of NE Ethiopia (Dallol; Long: 40.299351, Lat: 14.244367), representing an exceptional Mars analog due to diffuse hydrothermal alteration and the sulfate deposits evocative of past hydrothermal activity on Mars. This work aimed to obtain an identification map of minerals and their relative abundance using hyperspectral imaging to understand the potential of PRISMA as analog probe of Mars orbital instruments to detect and study possible analogs on Earth.</p> <p><strong>Study Area</strong></p> <p>Dallol is situated in the Danakil Depression, which is part of the East African Rift System. Principal geothermal features of the central crater area of Dallol are salt pillars, circular manifestations and acidic ponds. The northern and southern part is dominated by a salt dome structure and Salt pinnacles in the SW salt canyon area. The Black Mountain and the super-saline Black Lagoon, just south-southwest of Dallol, is an area of salt extrusions, geothermal manifestations and brine upflows.</p> <p>One advantage of this area is that the nebulosity is generally low, in fact the image selected during the dry season has a cloud coverage percentage of less than 1%. A salt suite was deposited and re-worked by hydrothermalism in the selected site. The characteristic minerals of the area are: carbonate, halite, carnallite and bischofite, anhydrite, gypsum, native sulfur of hydrothermal origin [5; 6].</p> <p>Flooding episodes from the Lake Assale to the north due to intense winds acting over the flat topography of the depression. The PRISMA SWIR Land/Water band combinations on the image selected, helped us to choose the region of interest around the Dallol area.</p> <p><strong>Operational Hyperspectral Processing</strong></p> <p>PRISMA images have three different levels of processing. Level 2C and 2D geolocated and atmospherically corrected images were used in this work and dated 21 August 2021. it is worth noticing that the images acquired on Dallol prior to the image selected for analysis had several preprocessing problems, particularly for stripe removal.</p> <p>The operational hyperspectral processing is composed of three main processing steps: (1) dimensionality reduction; (2) endmember identification and (3) mineral map distribution and abundance estimation.</p> <p>An unexpected result was obtained by applying an additional atmospheric correction, the Internal Average Relative Reflectance with Dark Subtraction, on the L2C image already corrected during the principal component analysis (PCA). The corrected atmospheric PCA allows better highlighting of geomorphological features.</p> <p>As for step (1), since hyperspectral images are composed of hundreds of extremely correlated bands, it is possible, and indeed beneficial, to reduce the effective dimension of the input data by removing bad bands.</p> <p>Step (2) was performed using the THOR Hyperspectral Material Identification (in ENVI 5.6) to identify unknown spectral signatures by comparing them with spectral libraries. This tool considers background statistics and image endmembers and can therefore provide accurate responses and spectra plots for rare or sub-pixel targets.</p> <p>Finally, the Spectral Angle Mapper (SAM) and the Linear Spectral Unmixing (LSU) tools were adopted for step (3). SAM determines the spectral similarity between two spectra by calculating the angle between the spectra and treating them as vectors in a space with dimensionality equal to the number of bands. LSU is a standard technique for spectral mixture analysis that infers a set of endmembers and fractions of these, called abundances. The mineral distribution and the abundance maps are shown respectively in Fig.1 and Fig.2.</p> <p><img src="" alt="" /></p> <p><strong>Conclusion</strong></p> <p>Six minerals have been recognised with the SAM classification from ENVI spectral library, in excellent agreement with the previous studies: carnallite, jarosite, kainite, polyhalite, gypsum and nontronite. The results confirm the mineralogical variability typical of the Dallol; in Fig.2, high mineral abundance values are shown in blue. The error calculated with the RMS is very low over the entire area of interest, except for the central zone where there are sulphur pools and therefore the presence of water does not favour this type of analysis.&#160;</p> <p>To better constrain the mineralogical mapping, future work will be conducted by a field exploration campaign to collect spectral signatures to be added to the ENVI library used, which so far could not be organised due to the ongoing civil war in Dankalia.</p> <p>To sum up, the study of terrestrial analogs can provide insights into the probable presence and nature of spring deposits on Mars, as well as help develop methods for classifying them from remote sensing data. PRISMA represents a valuable satellite for distinguishing not only the geometric characteristics of observed objects, but also the chemical-physical composition of the surface of the Earth.</p> <p><strong>References:</strong> [1] Walter, M.R. and Des Marais, D.J., 1993. Icarus 101:129&#8211;143 [2] Chang, C.I., 2007. John Wiley & Sons. 10.1002/0470124628 [3] Candela, L., et al. 2016. IEEE international geoscience and remote sensing symposium (IGARSS), 253-256. 10.1109/IGARSS.2016.7729057 [4] Loizzo, R., et al. 2019. IEEE (IGARSS), 4503-4506. 10.1109/IGARSS.2019.8899272 [5] Cavalazzi, B., et al. 2019. Astrobiology, 19(4), 553-578. 10.1089/AST.2018.1926 [6] L&#243;pez-Garc&#237;a, J.M., et al. 2020. Frontiers in Earth Science, 7, 351. 10.3389/FEART.2019.00351</p>
<p><strong>Introduction</strong></p> <p>The nature of the stress regime of the martian lithosphere that was active in the Late Noachian-Early Hesperian is a topic of ongoing debate [1]. The duality between the northern lowlands and southern highlands is thought to be a major relic of the early tectonic regime of Mars, however their exact origins and geological history is not fully constrained. Arabia Terra is a region that spans 4850 km across and is located in the transitional zone between the lowlands and highlands. It is known for widespread deposition of layered deposits [2, 3] within craters which are associated with past water activity [4]. Danielson is a 60 km diameter, 2 km deep, crater located in western Arabia Terra and centered at 8&#176;N, 353&#176;E (Figure 1A). The crater is dominated by the presence of a massive layered deposit which exhibits intense faulting and several large folds (e.g. Figure 1B, 1C, 1D).</p> <p>Danielson is unique to other craters in the region due to its quadrangular shape (Figure 1A and 1B). This shape cannot be easily explained by an impact event. Due to faulting that offsets the layered deposits and the crater rim, and high dips and folds, the crater likely has undergone extensive deformation. Since the deposition of these deposits is considered to have taken place in the Early Hesperian [5], we propose that the quadrangle shape of the crater rim, combined with post-depositional deformational structures, reflects the waning tectonic regimes during the Noachian-Middle Hesperian transition which was possibly a vestige of pseudo plate tectonics that never fully formed. The faulting and folding process may reflect the new successive tectonic regime that post-dates the closure of a pseudo plate tectonic era.</p> <p><strong>Methodology</strong></p> <p>An HRSC composite DEM [6] forms the base dataset of our study. We utilized three HiRISE DEMs and one HiRISE image for detailed measurements. 52 layer attitude measurements were obtained using Orion software and evaluated statistically based on strike and dip frequency (Figure 1D). Faults were identified by the lateral offset of layers and linear features. Folds were identified by interpreting large scale structures within layer sequences based on dip directions and 3D scenes.</p> <p><strong>Results</strong></p> <p>High layer dips, folds, and widespread faulting were identified and measured within Danielson. Two sets of dips, 4.5&#176; and 19.2&#176;, are present with a maximum dip of 44&#176; (Figure 1D). At least 12 folds were identified, each collinear and alternating from syncline to anticline (e.g. Figure 1E). All folds plunge to the southwest. Fold limbs are approximately 200 m long and contain on average 20 layers. Axial traces have a preferred northeast-southwest orientation. Over a hundred faults have been identified, many propagating through fold hinges (e.g. Figure 1E). Faults have two preferred orientations, northeast-southwest and northwest-southeast. Faults generally offset layering several meters, with some reaching 400 m.</p> <p>Danielson has a quadrangle shaped crater rim which does not conform to a circle or an oval (Figure 1B). Several regional faults pass through the crater and cross-cut the crater rim. The quadrangle shape and the fault/fold trend are not coaxial, suggesting a rotation in the tectonic stress regime between the two events.</p> <p><strong>Discussion</strong></p> <p>Dips are often above the angle of repose for material with a grain size that could be deposited by air or fluid-expulsion (34&#176;). Although there are many factors that contribute to the angle of repose (e.g., grain shape and moisture) [7], we interpret high dips as non syndepositional (i.e. not draping) and representative of a unique post-depositional history. Furthermore, the presence of tight folding in combination with widespread faulting demonstrates a period of intense deformation which possibly indicates regional extension and compression. Subsidence may have had a role in the observed deposit deformation because complex craters have a period of collapse and even uplift after impact, however the timescale of collapse is thought to be shorter in comparison with the accumulation rate of sediments [8].</p> <p>The quadrangle shape of the crater can be produced by the interaction of the impact stress and the stress regime of the lithosphere present at the time of impact (Middle-Late Noachian; 4.1-3.8 Gya) [9]. In this case it would be expected that the regional stress is characterized by northeast-southwest maximum horizontal extension and northwest-southeast maximum horizontal compression as explained by the contrast of the crater rim slightly changing from round to straight, normal to the extension direction (Figure 1B).<br /><br />This is further contested by the identification of faults and folds of the younger Early Hesperian aged (3.8 Gya) deposits within the crater that have preferred orientations north-northeast and south-southwest. It is likely that these structures are related to the tectonic regime which was present after the ending of the horizontal movement which produced the quadrangular shape of the crater. This change in the tectonic evolution of the region may well reflect the change from a type of plate tectonics regime to the present static stress.</p> <p>The stress regime revealed by the asymmetry of the crater can be a reflection of the last global tectonic (i.e. pseudo plate tectonics) framework which at the time of impact was ending. At the time of impact there was likely still a residual stress regime due to the horizontal movement at the boundary of the lowlands and highlands.</p> <p><img src="" alt="" width="1059" height="1145" /></p> <p>Figure 1.</p> <p><strong>References</strong><br /><br />[1] Hauber E. et al. (2010) Earth and Planet. Sci. Letters, 294(3-4), 393-410. [2] Schmidt G. et al. (2021) JGR: Planets, 126(11). [3] Annex A. M. and Lewis K. W. (2020) JGR: Planets, 125(6). [4]&#160; Andrews&#8208;Hanna J. C., et al. (2010) JGR: Planets, 115(E6). [5] Carr M. H. and Head J. W. (2010) Earth and Planet. Sci. Letters, 294(3-4), 185-20. [6] Heather D. et al. (2013a) Eu. Planet. Sci. Conf., 8. [7] Al-Hashemi and Al-Amoudi (2018) Powder&#160; Tech., 330, 397&#8211;417. [8] Melosh, H. J. and Ivanov, B. A. (1999) Annual Rev. of Earth and Planet. Sci., 27(1), 385&#8211;415. [9] Tanaka K et al. (2014) U.S. Geological Survey Scientific Investigations Map 3292.</p>
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