UTexas: 40-Year-Old Mystery Of Mars Northern Ice Cap Solved

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UTexas: 40-Year-Old Mystery Of Mars Northern Ice Cap Solved

Post by bystander » Wed May 26, 2010 6:44 pm

Planetary Scientists Solve 40-Year-Old Mysteries Of Mars' Northern Ice Cap
University of Texas, Austin - 26 May 2010
Scientists have reconstructed the formation of two curious features in the northern ice cap of Mars — a chasm larger than the Grand Canyon and a series of spiral troughs — solving a pair of mysteries dating back four decades while finding new evidence of climate change on Mars.

In a pair of papers to be published in the journal Nature on May 27, Jack Holt and Isaac Smith of The University of Texas at Austin's Institute for Geophysics and their colleagues describe how they used radar data collected by NASA's Mars Reconnaissance Orbiter to reveal the subsurface geology of the red planet's northern ice cap.

On Earth, large ice sheets are shaped mainly by ice flow. But on Mars, according to this latest research, other forces have shaped, and continue to shape, the polar ice caps.

The northern ice cap is a stack of ice and dust layers up to two miles (three kilometers) deep covering an area slightly larger than Texas. Analyzing radar data on a computer, scientists can peel back the layers like an onion to reveal how the ice cap evolved over time.

One of the most distinctive features of the northern ice cap is Chasma Boreale, a canyon about as long as the Grand Canyon but deeper and wider. Some scientists have suggested Chasma Boreale was created when volcanic heat melted the bottom of the ice sheet and triggered a catastrophic flood. Others have suggested strong polar winds, called katabatics, carved the canyon out of a dome of ice.

Other enigmatic features are troughs that spiral outward from the center of the ice cap like a gigantic pinwheel. Since they were discovered in 1972, scientists have proposed several hypotheses for how they formed. One suggested that as the planet spins, ice closer to the poles moves slower than ice farther from the poles, causing the semi-fluid ice to crack. Another used an elaborate mathematical model to suggest how increased solar heating in certain areas and lateral heat conduction could cause the troughs to self assemble.
View of the north polar region of Mars from orbit. The ice-rich polar cap (quasi-circular white area at center) is about 1,000 km across. It is bisected by a large canyon, Chasma Boreale, on the right side. Dark, spiral-shaped bands are troughs. Chasma Boreale is about the length of the Grand Canyon in the U.S. and up to 2-km deep. Credit: NASA/Caltech/JPL/E. DeJong/J. Craig/M. Stetson

Mars Northern Ice Cap Research Image Gallery

NASA Orbiter Penetrates Mysteries of Martian Ice Cap
NASA JPL MRO 2010-180 - 26 May 2010

Martian landmarks on the radar
Nature (27 May 2010) - Editor's Summary
The northern polar cap of Mars, containing enough water to cover the entire planet to a depth of several metres, features two major landforms that stand above all others. These are the enormous canyon, Chasma Boreale, and a series of spiral troughs. The processes leading to their formation have remained unclear. Now two papers in this issue present detailed histories of both systems. John Holt and colleagues use penetrating radar imagery from Mars Reconnaissance Orbiter's radar sounder to show that depositional processes — rather than a catastrophic event — formed the Chasma Boreale. Isaac Smith and John Holt use Mars Reconnaissance Orbiter data to rule out erosional cutting of polar ice as the cause of the central troughs, and instead conclude that they too are largely depositional, having migrated polewards and upwards in elevation in the past two million years.
The construction of Chasma Boreale on Mars Onset and migration of spiral troughs on Mars revealed by orbital radar

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Re: UTexas: 40-Year-Old Mystery Of Mars Northern Ice Cap Sol

Post by neufer » Wed May 26, 2010 7:36 pm

One would have supposed that katabatic winds coming out of the North Pole
would turn to the right from Coriolis force and thereby generate
right handed spirals rather than left handed spirals. :?:
Art Neuendorffer

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Science@NASA: Mystery of the Martian Spirals, Solved?

Post by bystander » Wed Jun 16, 2010 7:06 pm

Mystery of the Martian Spirals, Solved?
Science@NASA Headline News | 16 June 2010
Almost 40 years ago, NASA's Mariner 9 spacecraft relayed to Earth the first video images of Mars' northern polar ice cap, revealing a strange pattern of spiral swirls that has puzzled scientists ever since. Using new data from the Mars Reconnaissance Orbiter (MRO), researchers have finally uncovered the secrets of the troughs that snake through the ice cap like a spiraled maze.

Jack Holt of the University of Texas and his graduate student Isaac Smith used radar data from MRO's Shallow Subsurface Radar to crack the case. Examining the details of this new data set has laid open the ice cap's internal structure, revealing clues to the massive ice troughs' formation.

Apparently, the wind did it.

"Radar cross sections reveal layers of ice deposited throughout the ice cap's history," says Holt. "The size and shape of those layers indicate that wind has played a key role in creating and shaping the spiral troughs."

Not only does wind shape the spirals, but also it causes them to move. They rotate around the north pole, turning like a excruciatingly slow pinwheel, curiously enough, against the wind.

Smith explains the process: "Cold air from the top of the ice cap sweeps down the slope, gaining speed and picking up water vapor and ice particles along the way. As this wind blows across the trough and starts up the other slope (the cooler side, facing away from the sun), it slows and precipitates the ice it holds. All of this ice is deposited on this cool slope, building it up, so the trough actually grows and migrates, over time, against the wind."