View of Mars as might have appeared 2 billion years ago, with a low-latitude ocean filling the basin that now occupies the north polar region. The image was generated using data from the Viking & Mars Global Surveyor spacecrafts.
Credit: Tyler Perron
PARIS: Scientists firing the latest salvo of opinions over the mystery of Mars' water, say that massive volcanism might have tipped the Red Planet sideways – helping to back the theory that a mighty ocean once washed on the surface.
The theory – derived from photos snapped by orbiters and geological and chemical data sent home by the U.S. rovers Spirit and Opportunity – is that as much as a third of Mars' surface was once covered by water.
The cornerstone of this idea is that there are remarkable "shoreline" features visible in a ring thousands of kilometres long on the planet's northern hemisphere lowlands.
But there's a big problem: these intriguing features are at widely different altitudes, with elevation varying by several thousand metres (thousands of feet) instead of all being at "sea level" as they should be.
Mass redistribution
Harvard University scientist Taylor Perron and colleagues publish an article in the U.K. journal Nature today that argues that there is a reason for this discrepancy.
They believe massive volcanic events forced a redistribution of mass at Mars' surface, causing its poles to shift and tipping the planet sideways, if not quite upside down.
One such cause of this so-called 'polar wander' is an extraordinary extinct volcano, Tharsis, which bulges like a planetary beer belly.
With a volume of some 40 million cubic kilometres, Tharsis is 10,000 times bigger than Mauna Loa, Earth's biggest volcano, which rises nearly 10 kilometres from the floor of the Pacific Ocean to form the island of Hawaii.
When Tharsis was formed around 3.8 billion years ago, its huge load would have caused the planet to tip over so that the bulge could be comfortably accommodated at the equator, like a spinning child's top. One result of this shift, though, is that the planetary topography also goes for a wild ride, as internal stress thrusts up regions of land.
Volcanically massive
Tharsis, though, predates the Martian oceans by 900 million years or more, so this would not explain the different "shoreline" elevations.
That leaves two other, more recent, big candidates for polar wander, according to simulations made by Perron's team. One is the Elysium volcanic province, which lies in the opposite hemisphere to Tharsis, and the other is a massive basin, Utopia, buried beneath the vast northern plains.
As water is one of the ingredients to make life as we know it – and is also needed to sustain it – the riddle of the wet stuff has been central to investigations about Mars.
Recent observations from the fleet of U.S. and European orbiters posted around Mars indicate that there could be plentiful water ice lying below its dust, and some liquid water may also flow to the surface from time to time.
Still to be resolved, though, is what caused Mars to lose its precious ocean... if it ever had one.
shore lines
Shore lines on earth differ by many hundreds of metres as well. After each ice age sea level drops, shoreline shelfs get deeper.