Development of Chaos Terrain as Subaqueous Slide Blocks in Galilaei Crater, Mars

Chaos terrain, expressed as enigmatic blocky landscapes on Mars, has poorly understood origins. Several hypotheses have been put forward to explain chaos terrain formation, but none fully account for the morphologies observed in Galilaei crater, the focus of this study. Previously inferred to be a paleolake, Galilaei crater hosts chaos terrain composed of kilometer-scale, disorganized blocks around the southern and southeastern margin of the crater. Blocks are concentrated near the base of the crater wall, with blocks of decreasing size extending into the crater interior. The crater wall slope in regions where these chaos blocks are present is notably lower than in regions where blocks are absent. Based on the observed morphologies, we propose the chaos terrain in Galilaei crater formed by gravity-driven slope failure and down-slope transport as subaqueous landslides and mass flows, initiated at a time when the paleolake level was still high. We propose and discuss Earth analogs for the observed terrain and use mapping-constrained spatiotemporal relationships to reconstruct the sequence of landform development. Subaqueous landslides represent an uncommonly invoked mechanism to explain chaos terrain on Mars, reinforcing the idea that one mechanism cannot explain the diversity of this enigmatic terrain.

Fluvial geomorphology on Earth-like planetary surfaces: A review

Morphological evidence for ancient channelized flows (fluvial and fluvial-like landforms) exists on the surfaces of all of the inner planets and on some of the satellites of the Solar System. In some cases, the relevant fluid flows are related to a planetary evolution that involves the global cycling of a volatile component (water for Earth and Mars; methane for Saturn's moon Titan). In other cases, as on Mercury, Venus, Earth's moon, and Jupiter's moon Io, the flows were of highly fluid lava. The discovery, in 1972, of what are now known to be fluvial channels and valleys on Mars sparked a major controversy over the role of water in shaping the surface of that planet. The recognition of the fluvial character of these features has opened unresolved fundamental questions about the geological history of water on Mars, including the presence of an ancient ocean and the operation of a hydrological cycle during the earliest phases of planetary history. Other fundamental questions posed by fluvial and fluvial-like features on planetary bodies include the possible erosive action of large-scale outpourings of very fluid lavas, such as those that may have produced the remarkable canali forms on Venus; the ability of exotic fluids, such as methane, to create fluvial-like landforms, as observed on Saturn's moon, Titan; and the nature of sedimentation and erosion under different conditions of planetary surface gravity. Planetary fluvial geomorphology also illustrates fundamental epistemological and methodological issues, including the role of analogy in geomorphological/geological inquiry.

Volcano-ice interaction as a microbial habitat on Earth and Mars

Volcano-ice interaction has been a widespread geological process on Earth that continues to occur to the present day. The interaction between volcanic activity and ice can generate substantial quantities of liquid water, together with steep thermal and geochemical gradients typical of hydrothermal systems. Environments available for microbial colonization within glaciovolcanic systems are wide-ranging and include the basaltic lava edifice, subglacial caldera meltwater lakes, glacier caves, and subsurface hydrothermal systems. There is widespread evidence of putative volcano-ice interaction on Mars throughout its history and at a range of latitudes. Therefore, it is possible that life on Mars may have exploited these habitats, much in the same way as has been observed on Earth. The sedimentary and mineralogical deposits resulting from volcano-ice interaction have the potential to preserve evidence of any indigenous microbial populations. These include jökulhlaup (subglacial outflow) sedimentary deposits, hydrothermal mineral deposits, basaltic lava flows, and subglacial lacustrine deposits. Here, we briefly review the evidence for volcano-ice interactions on Mars and discuss the geomicrobiology of volcano-ice habitats on Earth. In addition, we explore the potential for the detection of these environments on Mars and any biosignatures these deposits may contain.