spacetoday.net: New evidence for past Martian ocean

Posted: Sun, Jun 17, 2007, 10:20 AM ET (1420 GMT)
Mars ocean elevation model (UC Berkeley)

A broad flat plain in the northern regions of Mars likely was once home to an ocean of liquid water, scientists reported this week. The basin had long been thought to have been the seabed for an ocean, but observations of the basin's edges revealed a "shoreline" that changed in elevation, which would not be the case if the basin had been filled with water. In a paper published in the latest issue of Nature, however, scientists said the undulating shoreline can be explained by taking into account the shifts in the planet's rotational axis over the last several billion years. Those shifts deform the planet's crust, creating the changes in shoreline elevation seen today. The polar shifts could have been created by thermal convection within the planet or even the creation and disappearance of the oceans themselves.