Red Planet Report

[Editor’s note: From a paper by Ngai Ham Chan and three co-authors recently published in the Journal of Geophysical Research.]

New Evidence of an Ancient Martian Ocean from the Global Distribution of Valley Networks

• Surface deformation due to True Polar Wander (TPW) events in the Martian history caused sea-level markers to deviate from a present-day equipotential level.
• Previous analyses of possible ancient sea-level markers on the Martian
surface reached opposing conclusions regarding whether TPW is necessary
to explain their topography.
• We revisit this issue by analyzing the elevations of another potential sea-level marker, the fluvial valley networks; our analysis supports the TPW scenario and, by extension, the possible existence of an ancient ocean.

Whether an ancient ocean existed on Mars has long been a controversial subject. On one hand, past conditions predicted by climate simulations suggested that Mars might not have been able to sustain liquid water for long periods of time. On the other hand, there is an abundance of surface features such as shorelines, deltas, sediments, and valley networks that suggest widespread and persistent liquid water on Mars.

While the features believed to trace out ancient shorelines do not lie on the same elevation today, they could have been shifted vertically by the movement of Mars’ rotation pole (which caused a shift in the equatorial bulge) or by the formation of Tharsis ‐ a cluster of large volcanoes.

In this study, we present a new set of possible sea‐level markers: the valley networks that may have drained directly into an ancient northern ocean. We find that the elevations of these valley networks, along what would have been the shore of the northern ocean, are consistent with them being ancient sea‐level markers that had been subsequently shifted vertically by some combination of changes in Mars’ rotation pole and the growing Tharsis volcanic bulge. [More at link]