MNN - Mother Nature Network

Astronomers on Wednesday said they could explain a nearly four-decade-old enigma surrounding rugged troughs and a chasm in the northern ice cap of Mars that could comfortably house the Grand Canyon.

 

The Red Planet's northern cap measures around 600 miles across, with layers of ice and dust stacked up to 2 miles deep.

 

It also has two remarkable features that have puzzled scientists ever since they were exposed in detail by U.S. probes almost 40 years ago.

 

One is the Chasma Boreale, a depression 310 miles long, up to 100 kms 60 miles wide and 1.2 miles deep.

 

Many experts have surmised that the Chasma Boreale was created by volcanic action that melted the bottom of the ice sheet, triggering a flood that gouged out this mighty gash in Mars' surface.

 

Another mystery is a spiral of troughs that radiate out through the polar cap, rather like a pinwheel.

 

Its strange symmetry caused some experts to wonder whether the troughs were formed by a centrifugal force caused by the spinning of the planet.

 

According to this theory, ice that is closest to the pole moves slower than ice that is further from the pole. As a result, the semi-fluid ice tensed and broke, twisting into spirals as it did so.

 

But papers published in the journal Nature say both hunches are wrong — and the answer to the riddle is both simple and complex at the same time.

 

A team led by geophysicists Jack Holt and Isaac Smith of the University of Texas at Austin used radar data from a latterday NASA scout, the Mars Reconnaissance Orbiter, that probed the cap's subsurface topography.

 

The picture that emerges is a lost landscape that sweeps aside the idea of the northern polar cap as neat, cake-layered geology.

 

Instead, the subsurface is riddled with many complicated features, ranging widely in thickness and orientation.

 

It points to an ancient process, over millions of years, by which the ice and dust accreted while at they same time were sculpted by a powerful, persistent force: the Martian wind.

 

"Nobody realized that there would be such complex structures in the layers," Holt said.

 

"The layers record a history of ice accumulation, erosion and wind transport. From that we can recover a history of climate that's much more detailed than anybody expected."

 

The Chasma Boreale, far from being born in a catastrophic event, occurred through an aeons-long process, the scientists believe.

 

Wind eroded a gap in a base layer of soft sand and ice, rather like a river on Earth cuts its way through a valley, relentlessly exploiting the softest rock.

 

Further deposits of ice and dust then accumulated on either side of the gap, creating the slopes of the canyon.

 

As for the spiral troughs, the distinctive swirl was created by the Coriolis force, a well-known phenomenon on Earth in which winds are deflected by the planet's spin.

 

Copyright 2010  AFP Global Edition