Earth-Like Process Found on Mars
By Larry O'Hanlon, Discovery News


Oct. 24, 2005— The first complete magnetic map of Mars is showing signs that the Red Planet once may have had plate tectonics — a very Earth-like planetary resurfacing and mountain-building process.

The presence of brittle rocky crustal plates moving atop a denser, viscous mantle has not been firmly established on any other world than Earth.

Here at home it's seen as a critical process for, among other things, keeping volcanoes at work spewing out gases that help replenish the oceans and atmosphere. Paleontologists have also credited plate tectonics with stimulating life to continually adjust to changing landscapes and climates.

The evidence of plate tectonics on Mars are zebra stripes of reversing magnetism seen in the southern hemisphere.

Those stripes suggest that the crust there was once being pulled apart and lava regularly surged up from below to form new crust and fill the gap, said Jack Connerney, co-investigator for the Mars Global Surveyor magnetic field investigation at NASA's Goddard Space Flight Center.

The same sort of thing is still going on today at the Mid-Atlantic Ridge, a tectonic boundary that splits nearly the entire Atlantic Ocean north to south.

And also similar to the Mid-Atlantic Ridge, bands of magnetized lava rocks in Mars' crust record which way the flip-flopping global magnetic field was aimed when the rocks cooled and solidified.

"The magnetism that's seen in the Martian crust has to be at least an order of magnitude greater than on Earth," said Connerney.

That makes the magnetism easier to detect and measure from 250 miles up, where the spacecraft orbits. What also makes it easier, he said, is the fact that Mars no longer has a significant magnetic field creating a lot of magnetic noise. The spacecraft detected all remnant magnetism of global fields that died out billions of years ago.

The new magnetic map of Mars made its debut in a recent issue of the Proceedings of the National Academy of Sciences.

If Connerney is correct and the magnetic bands are evidence of a once-spreading plate boundary on Mars, they may also explain other features. They could explain why the volcanoes of the Tharsis region lie in a straight line, for instance.

Lines of volcanoes are common on Earth along faults in regions where the plates are spreading apart, as well as alongside places where one crustal plate dives under another. Mount St. Helens and its siblings in the Pacific Northwest are an example of the latter sort of volcanic line.

Still, plate tectonics on Mars is not a done deal, say some other Mars researchers.

"I think it's useful," said geophysicist Norm Sleep of Stanford University, who has previously tried to fit plate tectonics to Mars' northern hemisphere with earlier, more limited magnetic maps. "I'm not convinced it indicates plate tectonics, but that's a reasonable hypothesis."

Discovery News original article