Planetary science: Water on Mars revisited


There may once have been an ocean of water on the surface of Mars after all. A change in the planet’s orientation could explain some features controversially interpreted as ancient martian shorelines.
Some think that the northern plains of Mars, covering nearly one-third of the planet’s surface, may have contained an ocean in the distant past. The most provocative piece of evidence for this is a set of surface features that ring the plains for thousands of kilometres, which have been interpreted as a series of former shorelines. But these ‘shorelines’ vary in elevation by up to several kilometres, instead of all being at ‘sea level’, casting doubt on this theory.
J. Taylor Perron and colleagues now show that true polar wander — a change in the orientation of the surface of a planet with respect to its rotation pole — could explain the elevations of the proposed shorelines, reviving the hypothesis that an ancient ocean once covered a large part of the martian surface.
CONTACTJ. Taylor Perron (Harvard University, Cambridge, MA, USA)
Tel: +1 617 495 4687; E-mail: perron@eps.harvard.edu

Maria T. Zuber (Massachusetts Institute of Technology, Cambridge, MA, USA) N&V author
Tel: +1 617 253 6397; E-mail: zuber@mit.edu