Mars: new insights and unresolved questions

Mars exploration motivates the search for extraterrestrial life, the development of space technologies, and the design of human missions and habitations. Here, we seek new insights and pose unresolved questions relating to the natural history of Mars, habitability, robotic and human exploration, planetary protection, and the impacts on human society. Key observations and findings include: – high escape rates of early Mars’ atmosphere, including loss of water, impact present-day habitability; – putative fossils on Mars will likely be ambiguous biomarkers for life; – microbial contamination resulting from human habitation is unavoidable; and – based on Mars’ current planetary protection category, robotic payload(s) should characterize the local martian environment for any life-forms prior to human habitation.Some of the outstanding questions are:– which interpretation of the hemispheric dichotomy of the planet is correct; – to what degree did deep-penetrating faults transport subsurface liquids to Mars’ surface; – in what abundance are carbonates formed by atmospheric processes; – what properties of martian meteorites could be used to constrain their source locations; – the origin(s) of organic macromolecules; – was/is Mars inhabited; – how can missions designed to uncover microbial activity in the subsurface eliminate potential false positives caused by microbial contaminants from Earth; – how can we ensure that humans and microbes form a stable and benign biosphere; and – should humans relate to putative extraterrestrial life from a biocentric viewpoint (preservation of all biology), or anthropocentric viewpoint of expanding habitation of space?Studies of Mars’ evolution can shed light on the habitability of extrasolar planets. In addition, Mars exploration can drive future policy developments and confirm (or put into question) the feasibility and/or extent of human habitability of space

Geomorphic evidence of lobate deposits in gullies on Mars - global survey using HiRISE images

International audienceGullies on Mars, found between 30˚-75˚ in both the hemispheres, represent steep slope drainage systems comprising an alcove, a channel and a depositional apron [1]. Lobate deposits similar to those found in terrestrial debris-flow gullies have been observed in martian gullies, consequently researchers suggested that water-bearing debris-flows likely formed martian gullies. However, since there are only few sites on Mars where the evidence of lobate deposits is preserved, and recent observations have revealed present-day modifications in martian gullies that result in features akin to water-bearing debris-flows [2], sublimation of seasonal CO2-frost has been suggested to drive gully formation [2]. Thus, water has been suggested to never have been involved in gully formation [2], thereby raising a question whether lobate deposits are from wet (water-bearing) or dry (CO2-frost) flows. To decipher whether the CO2-frost driven mechanism has formed the entire suite of gullies, we have conducted geomorphic investigation utilizing the High Resolution Imaging Science Experiment (HiRISE) images of the craters emplaced between 30˚-75˚ in both the northern and southern hemispheres to document evidence of overlapping lobate deposits. We primarily aim to infer whether the geomorphic evidence of overlapping lobate deposits are widespread and whether their presence reflects a global climate signal. Furthermore, we aim to understand the orientation preferences and slope ranges of crater walls on which lobate deposits are found and examine whether the age of the craters containing evidence of lobate deposits influence their formation and distribution. We have found 20 new sites (on crater walls) on Mars (6 in the north and 14 in the south) in which unambiguous lobate deposits are preserved. Overlapping lobes are evident at all the sites, such as stacking of relatively small-sized individual lobes or laterally elongated lobes at the fan termini or at the fan surface. We use the most up-to-date global data on gully orientation [3] to compare the orientation of sites with gullies and those with lobate deposits. We measure the slope of surfaces dominated with overlapping lobes using digital terrain models (DTM) from Context camera (CTX) stereo images and compare them with previously reported values of slopes estimated for lobate deposits [4-5]. The crater age will be used to infer if there is a preference for a time-period during which the lobate deposits are emplaced. Together, we will use our observations to decipher the origin of lobate deposits, and examine the possible role of water to critically assess the hypothesis that present-day CO2-frost driven processes can explain the formation and evolution of entire suite of martian gullies. [1] M.C. Malin, K.S. Edgett, Science 288 (2000) 2330-2335. [2] C.M. Dundas, A.S. McEwen, S. Diniega, C.J. Hansen, S. Byrne, J.N. McElwaine, Geol. Soc. Lond. Spec. Publ. 467 (2017). [3] S.J. Conway, T.N. Harrison, R.J. Soare, A.W. Britton, L.J. Steele, Geol. Soc. Lond. Spec. Publ. 467 (2017). [4] A. Johnsson, D. Reiss, E. Hauber, H. Hiesinger, M. Zanetti, Icarus 235 (2014) 37-54. [5] T. De Haas, D. Ventra, E. Hauber, S.J. Conway, M.G. Kleinhans, Icarus 258 (2015) 92-108

Evolutionary history of western Eos Chaos of Valles Marineris, Mars: Insights from morphological characteristics

The dynamics of aqueous processes within the Eos Chasma region in the trough of Valles Marineris on Mars have been attributed to a variety of Hesperian-aged landforms. We aim to improve the understanding of the geological characteristics of the western part of the Eos Chaos by investigating the morphological, topographical, and thermo-physical characteristics of the western semi-circular segment of Valles Marineris. The western Eos Chaos is characterized by remnants of an elevated crater rim, a central peak, and a circular boundary. Based on these observations, we infer that the study area is an ancient, highly degraded impact crater. Our observations indicate that numerous geological processes, such as fluvial, tectonic, and aeolian processes, have shaped the landforms. For instance, channels on the slope of the wall with a mean v-index of 0.2 indicate a fluvial origin. The chaotic mounds within the study regions are highly degraded. However, the presence of eroded inselberg peaks above the maximum ponding level of eastern Valles Marineris (–3560 m) suggests that both aeolian and fluvial processes have played a role in the denudation of the impact crater. Furthermore, both aeolian and fluvial processes also influenced the morphological evolution of inselbergs of this impact crater of Eos Chaos. The morphological, topographic, and thermal inertia characteristics of the landforms in the Eos Chaos are similar to those found elsewhere in Valles Marineris. In this study, the impact crater of Eos Chaos is considered a sub-region of Valles Marineris, in which evidence for many past geological processes is preserved. Based on possible chronological markers, we have developed a model that explains the evolution of the Eos Chaos impact crater and its incorporation into Valles Marineris

Morphologic and morphometric differences between gullies formed in different substrates on Mars: new insights into the gully formation processes

International audienceMartian gullies are kilometer-scale, geologically young features with a source alcove, transportation channel, and depositional fan. On the walls of impact craters, these gullies typically incise into bedrock or surfaces modified by the latitude-dependent mantle (LDM; inferred as consisting of ice and admixed dust) and glaciation. To better understand the differences in the alcoves and fans of gullies formed in different substrates and infer the flow types that led to their formation, we have analyzed the morphology and morphometry of 167 gully systems in 29 craters distributed between 30 and 75°S. Specifically we measured length, width, gradient, area, relief, and relief ratio of the gully alcoves and fans; Melton ratio, relative concavity index, and perimeter; and form factor, elongation ratio, and circularity ratio of the gully alcoves. Our study reveals that gully alcoves formed in LDM/glacial deposits are more elongated than the gully alcoves formed in bedrock, and they possess a distinctive V-shaped cross section. We have found that the mean gradient of fans formed by gullies sourced in bedrock is steeper than the mean gradient of fans of gullies sourced in LDM/glacial deposits. These differences between gullies were found to be statistically significant and discriminant analysis has confirmed that alcove perimeter, alcove relief, and fan gradient are the most important variables for differentiating gullies according to their source substrates. The comparison between the Melton ratio, alcove length, and fan gradient of Martian and terrestrial gullies reveals that Martian gully systems were likely formed by terrestrial debris-flowlike processes. Present-day sublimation of CO 2 ice on Mars may have provided the adequate flow fluidization for the formation of deposits akin to terrestrial debris-flow-like deposits

Geological characterization of Chandrayaan-2 landing site in the southern high latitudes of the Moon

ISRO's lunar orbiter-lander-rover mission Chandryaan-2 is scheduled to be launched in the mid of 2019. In this contribution, we have carried out detailed geological characterization of the prime landing site (70.9°S, 22.8°E) of the Chandrayaan-2 lander – “Vikram”. The proposed landing site is located amidst the nearside lunar highlands at high southern latitudes, which is ~350 km north of South Pole Aitken (SPA) basin rim. Topography of the region is generally flat and it is largely confined by craters of varying diameter. The majority (94%) of the landing ellipse (~15 × 8 km) is within the boundary of intercrater plains with a slope <15° and yields a crater retention age of ~3.7−0.04+0.03 Ga. Craters (diameter: ~2.28 m to ~1.13 km) consistent with morphologies varying from fresh to degraded are common within the landing ellipse, though the ellipse center is devoid of craters with significant depth. Analysis of the spectral reflectance data suggests that the landing ellipse is dominantly feldspathic/highland material. The estimated average abundance of elements within the landing ellipse are Fe: 4.2 wt%, Mg: 5.4 wt%, Ca: 10 wt%, and Ti: 0.3 wt%. Results indicate that the surface composition might correspond to FAN dominated material. Based on elemental and spectral analysis results, we envisage possible mixing of highland material with ejecta from multiple craters surrounding the landing ellipse and/or SPA basin, resulting in hybridisation of highland regolith. Together, the results provide a contextual framework for in situ investigations at the proposed landing site