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We conducted comparative morphological analysis of gullies within two high-latitude Martian craters (Domoni and Maricourt) in the northern hemisphere of Mars with (1) the debris-flow gully systems in the Ladakh Himalaya and (2) Istok Crater in the southern mid-latitudes of Mars where water-bearing debris-flow deposits have been previously reported. Our findings suggest that the debris-flow landforms preserved on gully and alluvial fans in the Ladakh Himalaya are potential analogues for the deposits preserved over the equator-facing slopes of Domoni and Maricourt Craters. Further, we found that the morphological attributes of channels and deposits (including overlapping terminal lobes, levées, tongue-shaped/lobate deposits and broad/small depositional deposits) within both the study craters and Istok Crater are similar. As a result, the studied craters emerge as additional sites in which possible evidence of water-bearing debris-flows are preserved on Mars. By comparison to our Earth analogue, we further propose that episodic melting of snow accumulated within the sheltered alcoves is the most likely source of water for the formation of such gullies. Taken together, our findings suggest that debris-flow may not be a rare process in gully formation on Mars and evidence may be preserved in other unexplored areas.

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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.