Young Valley Networks on Mars: Persistent Flow of Water in Lyot Crater, an Amazonian Impact Basin Microenvironment

Introduction: While Amazonian fluvial landforms are not abundant on Mars, remote sensing data have revealed details regarding the role of ice in non-polar regions in the Amazonian. Evidence includes 1) deposits interpreted to be remnants of cold-based glaciers at low-and mid-latitudes [1-6]; 2) mantling deposits interpreted to be a desiccating layer of ground ice [7-8]; 3) laterally-expansive units of water ice in the top-meter in the mid-and high-latitudes in each hemisphere [9-10]; and 4) viscous flow features interpreted to be the product of glacial-like flow along steep val-ley/crater walls [11-12]. Under peak conditions, the surface of Mars straddles the triple point of water, which motivated us to investigate the most-likely locations/microclimates for melting of these surface/near-surface ice features [13-14]. Large-scale impact craters at low elevations and mid-latitudes provide particularly optimal conditions, with 1) relatively high surface pressure, 2) reasonable solor insolation conditions and 3) the possibility of residual thermal anomalies from the impact event itself. Lyot Crater, a ~215 km peak-ring impact basin in the northern lowlands of Mars (50°N, 30°E) was the first target of our survey as it provides an environment that meets all of these constraints. We analyzed recently obtained CTX data to document evidence of remnant glacial deposits and surface features that appear indicative of melting and drainage. Description: The floor of Lyot shows evidence for several sinuous valley networks that have been incised exclusively into an expansive stippled mantling unit that blankets the majority of the Lyot crater floor. Twenty separate networks are observed in CTX and THEMIS data, 15 of which occur in the eastern half of Lyot. The valleys range in length from short, 2 km long, isolated valleys to 50 km long networks which have widths averaging ~250 m. Valley floors are smooth at CTX resolution, in contrast to the adjacent stippled mantling unit. Profiles extracted from the Mars Orbiter Laser Altimeter (MOLA) data set show that the valleys follow the local topographic gradient downslope. Regional slopes in the down-valley direction range from 0.36° to 6.12°, but most networks trend around the median for all valleys of 1.93°. Valleys start at a wide range of elevations, from ~-2883 m to ~-5684 m (mean =-3803 m). Valley walls appear uniformly fresh and no impact craters or ejecta blankets are observed on any of the valley floors. Valleys emanate from the upslope margins of the stippled mantling unit and from the termini of lobate …