Geoscientist Online 27 June 2007
Emily Baldwin sails the vanished ocean of Mars
Despite the overwhelming chemical and geological evidence for water on the surface of Mars, the spatial extent and the temporal persistence of the surface water during the planet’s early years remains unclear. The major point of scepticism lies in the observation that if the oceans were contained within the shorelines visible today, the sea level couldn’t have been – well – level. Indeed, the peaks and troughs along the proposed shorelines - Deuteronilus and Arabia - have topographic differences of up to 3km. In contrast, ancient shorelines on the Earth remain relatively flat, which provides some of the cynicism directed at the advocates of the Martian shoreline theory.
In the 14 June 2007 issue of Nature, however, a team of Canadian and American researchers led by Dr Taylor Perron uncover new evidence that the observed features on the Martian surface really are shorelines of massive oceans that covered as much as one-third of the planet. The team present a quantitative analysis that explains the topography by a shift in the planet’s spin axis occurring within the last 2 to 3 billion years.
Any major shift in planetary mass, whether it is on the surface or in the planet’s interior, could cause a shift of the rotation axis because a spinning body is most stable with its mass farthest from its spin axis. Perron et al. postulate that a flood of water may have filled the Arabia Ocean, perhaps to a depth of up to 700 metres. The resultant mass at the pole might have been enough to shift the pole further south by 50 degrees (approximately 3000 km). Once the water disappeared, the pole could have wandered back, and subsequently shifted again in the deluge that created the Deuteronilus shoreline. Spinning planets bulge at the equator and solid surfaces deform differently to liquid sea surfaces. As a result, the surface topography of the shorelines would have deformed as the planet’s rotation axis shifted.
What may have happened to this huge volume of water since remains an open question. Perron speculates that the oceans may have gradually converted into water vapour, moved to higher elevations and flowed beneath the surface, where they are awaiting discovery. Despite the huge advances made possible by the heroic efforts of the Mars Exploration Rovers and various orbiters, understanding Mar’s watery past is still far from complete.
Article reference
Perron et al. Evidence for an ancient martian ocean in the topography of deformed sediments. Nature 447, 14 June 2007.