Reassessing the Ancient Martian Ocean Hypothesis Using the Global Distribution of Valley Networks

Topography has been central to investigations of a possible ancient Martian ocean. Some studies have used topography to suggest that sea level markers are consistent with a present-day equipotential (for example, using deltaic deposits: Achille & Hynek, Nature Geosci., 2010), whereas others have found that large-scale deformations must have occurred if sea level markers fell on an equipotential in the past (for example, using mapped shorelines: Perron et al., Nature, 2007). We revisit this issue by examining another possible equipotential marker, the fluvial valley networks observed on the Martian surface. The locations and elevations of valley termination points, especially near the dichotomy boundary, shed additional light on whether the existence and extent of an ancient Martian is consistent with present-day topography.