THE MARS OCEAN HYPOTHESIS: RESEARCH OBJECTIVES AND APPROACH

The objective of this work is a better understanding of the origin, timing, and ultimate fate of an Early Mars ocean. We will evaluate our updated global map of proposed paleo-shorelines, to assess their departures from horizontality, and infer what that says about the spatial accuracy of the mapping and the appropriateness of the global datasets used. To first approximation, the mapped shorelines do appear to define nearly-planar surfaces averaged globally, but the local details show scatter of tens to hundreds of meters over distances of kilometers to tens of kilometers. The long-wavelength variations could indicate important tectonic and isostatic deformations of once-horizontal surfaces. The shorter wavelength scatter could suggest a number of possible causes: 1) placement of the shoreline shapefiles needs improvement; 2) the resolution of the DEM is insufficient at large scales to provide accurate elevations for the shapefiles at these scales; and 3) there have been real, short wavelength changes to the topography that have affected the elevation of the shapefile vertices (e.g., fault scarps, wrinkle ridges). To address these factors, the evaluation of the mapped shorelines will include local assessments at large GIS map scales if the shapefile appears too generalized with respect to available high spatial resolution image and topography data.

The analysis of the global shoreline shapefiles will include these steps: 1) measure the volume contained within the surfaces defined by the proposed shorelines to provide comparisons with model estimates of Mars’ water inventory over time (i.e., did Mars accrete and outgas a sufficient volume of water, or was some of it introduced during Late Heavy Bombardment); 2) use published ages from global geologic maps of surrounding surfaces to determine approximate ages for each shoreline; 3) address whether long-wavelength departures from horizontal point to global tectonism, polar wander, or isostatic adjustments post-ocean.