Richard B. Roberts Fellow Isamu Matsuyama and colleagues published a paper entitled "Evidence for an Ancient Martian Ocean in the Topography of Deformed Shorelines" in this week's issue of Nature. The group's observations suggest that the northern plains of Mars that cover nearly one third of the planet's surface, may once have contained an ocean. Their research suggests that changes in Mars' orientation with respect to its axis might be responsible for large variations in the topography of shoreline-like features on the planet. Though scientists have studied these features for more than 30 years, this current study presents an alternative explanation for how they formed.

According to the Carnegie Institution press release, irregularities in proposed Martian shorelines discovered by geophysicists in the past might be explained by surface deformation from "true polar wander"--a phenomenon in which Mars' spin axis and poles shifted by nearly 3,000 kilometers along the surface sometime within the past 2 or 3 billion years. Spinning planets bulge at their equator and their solid surfaces deform differently than liquid sea surfaces. The results are deformations in the topography of the shorelines as the planet's rotation axis shifted.

NASA's Mars Global Surveyor spacecraft mapped the Martian topography in the 1990s, finding that ancient shorelines--known as Deuteronilus and Arabia-- aged between 2 and 4 billion years, varying in elevation by about a half of a mile and more than a mile and a half, respectively. Changes in shoreline elevation on Earth are more slight in contrast, leading many experts to argue against their connection to past oceans on Mars.

Matsuyama--who developed models for true polar wander driven by internal and surface processes on Mars--commented, "A similar scenario to what we are proposing on Mars has been used to explain sea level variations--deformed shorelines--over geologic time scales of 1-100 million years on Earth, but the deformations along Deuteronilus and Arabia are quite dramatic, so the connection has not been an easy one to make. We believe this work significantly strengthens the case for large Martian oceans in the ancient past."