No abstract

The Martian North Polar Layered Deposits (NPLD) are composed of alternating water-ice and dust layers resulting from atmospheric deposition and are key to understanding Mars’ climate cycles. Carved within these deposits are spiral troughs, whose migration affects deposition signals. To understand the relationship between NPLD stratigraphy and Martian climate, we must first identify the modern-day drivers of NPLD ice migration. The prevailing theory posits migration is driven by upstream-migrating bed undulations bounded by hydraulic jumps, caused by katabatic winds flowing over trough walls with asymmetric relief in cross-section. This is supported by trough-parallel clouds, whose formation can be first order attributed to hydraulic jumps. We present an updated cloud atlas across the Martian north pole using ~13,800 Thermal Emission Imaging System images spanning ~18 earth years. We find evidence of trough-parallel clouds in ~400 images, where regions nearer to the pole have the highest cloud frequency. We also compare spiral trough geometry (i.e., trough wall slopes and relief, width, depth) to our cloud atlas. We find regions with trough-parallel clouds often correlate with metrics suggested to be associated with modern-day erosion-deposition cycles (i.e., wall relief and asymmetry), but not always, and in some regions, troughs with morphologies conducive to cloud formation have no clouds. Overall, we show trough geometry to vary greatly across the deposits, both within and between troughs, suggestive of localized differences in deposition relative to migration, varying katabatic wind intensities, or the possibility of additional mechanisms for trough initiation and migration (e.g., in-situ trough erosion).

Past environments on Mars contained abundant water, suggesting certain regions may have been conducive to life as we know it and implying the potential for microbial inhabitants. Gale and Jezero craters, home of the Perseverance and Curiosity rovers, hosted ancient lakes that experienced periods of active hydrologic cycling and prolonged drying intervals. Exploration of these basins (and future operations on Mars) will benefit from detailed characterizations of analogous environments on Earth, where life detection strategies at various spatial scales (i.e., rover to orbiter) can be tested and validated. Investigations of terrestrial analogs are critical for understanding (1) how microorganisms generate chemical biosignatures in environments characterized by multiple extreme conditions; (2) the impact of environmental conditions and mineralogy on biosignature preservation; and (3) what technologies and techniques are needed to detect biosignatures remotely or in situ. Here, we survey five terrestrial sites analogous to climate conditions proposed for Late Noachian to Early Hesperian Mars, when craters are thought to have hosted active lakes. We review the geologic setting, environmental conditions, microbial habitability, extant microbial communities, and preserved biomarkers at each analog and discuss their relevance to the search for signs of life in Martian craters with in situ and remote instrumentation. The analogs range from active to desiccated lake systems, temperate to hyper-arid climates, and have acidic to neutral-pH and hypo- to hyper-saline waters. Each analog hosts microorganisms adapted to multiple extremes (polyextremophiles), including aspects of water availability (i.e., surface waters versus shallow subsurface water versus groundwater) and physiochemistry (e.g., water activity, salinity, temperature, alkalinity, pH, and redox potential) that can form macrobiological features such as microbial mats. Comparing the expected achievable spatial resolution of several key Mars instruments to the spatial extent of macrobiological features at each analog reveals that most features are unlikely to be resolved from orbit and require rover-scale instruments for detection. We recommend that future studies at these analogs use multi-scale remote sensing surveys to determine thresholds for detecting macrobiological features and map how patterns in mineralogy or physical characteristics of environments correlate to modern-day microbial communities or preserved biomarkers. It will also be critical to determine how the characteristics of macrobiological features, such as areal extent, percent cover, thickness, pigments, etc., impact detectability thresholds. These findings can provide vital information on potential topographic or spectroscopic signatures of life, and at what scales they are detectable. This research is critical to guide sample collection locations within craters like Jezero, and for selecting landing sites for future missions in evaporative Martian basins and other rocky bodies.