Investigating controls on martian alluvial fan formation

Martian alluvial fans provide compelling evidence for surficial fluvial activity that persisted into the Amazonian Period, challenging widely held paradigms of Mars’ climate history and raising the prospects for the planet’s relatively recent habitability. Alluvial fans are primarily located within large impact craters in the southern highlands (between 0° and 40° S) but are limited in their geographic distribution, with high concentrations in southwestern Tyrrhena Terra, southern Margaritifer Terra, and southwestern Terra Sabaea. Previous work has found that martian fans formed over many thousands of years from precipitation-fed runoff. However, the reasons for their limited geographic distribution and the prevailing conditions during fan formation remain poorly understood.

Our goal is to constrain the topographic and climatic conditions necessary to initiate alluvial fan formation on Mars. We will use high resolution digital elevation models to examine physiographic differences between fan-hosting and fan-absent craters. We aim to test the hypothesis that fans required high relief source watersheds (and thus relatively fresh impact craters) upon which to form. We will further test this hypothesis with the MARSSIM landform evolution numerical model, which will also allow us to assess the range of climatic conditions present during fan formation (e.g., wet enough for sediment transport but arid enough that lakes do not inundate the alluvial fans). We will additionally provide hard constraints on the total era of fan formation by using crater counts to date both fan surfaces and their enclosing crater basins and determine whether fan formation occurred concurrently across Mars. Accomplishing these tasks will provide insights into the hydrologic and climatic environment on Mars during the Late Hesperian and Early Amazonian Periods.