May 20, 2008 -- A closer look at the remnants of mid-latitude glaciers on Mars has revealed signs of deep, icy rivers in the recent geologic past, say researchers who have published the discovery in the May issue of the journal Geology.
Mars glaciologist James Dickson of Brown University and his colleagues followed the trail of telltale glacial remnants at the edges of Mars' northern lowlands and were surprised to find signs that a glacier once traveled in a direction now uphill, toward a canyon's edge. Unless the glacier somehow defied gravity, the only explanation is that it was once higher than the canyon.
"What we see right now is a glacier that looks like it flowed uphill," Dickson told Discovery News. "That can't happen."
To make the features conform to gravity, the researchers imagined filling a neighboring valley with ice so high that it could then flow down toward this canyon. The current uphill appearance is the result of most of the ice evaporating away, leaving debris and the surface features seen today.
"We are very confident that there was a kilometer of ice at this location," said Dickson. Nearby lowlands would also have been filled with ice, in some areas two kilometers deep, he explained. The expansive ice sheet was perhaps comparable to what covered North America during the last Ice Age.
"They are pretty much on target," said Mars researcher Jeffery Kargel of the University of Arizona of the Dickson's conclusions. What's more, he said, there's no reason to believe all the ice is gone from these glaciers.
"The morphology indicates to me that there's still a lot of ice there." Kargel told Discovery News. "These are glaciers that are alive and kicking. They're probably still very, very slowly chugging along."
The discovery of the glaciers comes as a result of more and better images of the Martian surface, along with detailed elevation data collected by the Mars Orbiter Laser Altimeter. Without the elevation data, it would be very difficult to see the strange uphill turn.
The waxing and waning of such gigantic, mid-latitude glaciers tens of millions of years ago fits with a scenario advocated by Dickson's colleague and co-author James Head, also of Brown University.
According to Head, the cause of the climate fluctuations is the very wide and gradual wobble of Mars' spin axis, which, unlike Earth's axis, is not stabilized by a large moon.
Over the ages, Mars' wobble sometimes tilts the planet's poles lower and closer to the sun. This melts the polar ice and sends the water snowing down on the cooler mid-latitudes. We just happen to be looking at Mars at a time when its spin axis is gently tilted, so it resembles Earth with ice concentrated primarily at the poles.
"There is a really wide recognition, near consensus, that Jim Head (et al.) are really on target with this idea of glaciation on Mars," said Kargel.
Further details on Mars ice will no doubt be arriving shortly. NASA's Phoenix Mars lander is zeroing in on the unexplored arctic region, where a reservoir of ice is thought to lie hidden underground. Phoenix is expected to land on Sunday.
Discovery News will be blogging live from the Phoenix flight control center at the Jet Propulsion Laboratory in Pasadena, Calif., beginning Thursday, May 22
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