Chasms on Mars
Large sheets of ice and snow form on the poles of both Earth and Mars. On Earth their formation is shaped by ice and water flows. On Mars there is an oddness of spiraling troughs and a giant canyon. What in the climate of Mars does this? Data from NASA's Mars Reconnaissance Orbiter have helped scientists solve a pair of mysteries dating back four decades and provided new information about climate change on the Red Planet.
The Shallow Radar, or SHARAD, instrument aboard the Mars Reconnaissance Orbiter revealed subsurface geology allowing scientists to reconstruct the formation of a large chasm and a series of spiral troughs on the northern ice cap of Mars. The findings appear in two papers in the May 27 issue of the journal Nature.
Decades ago scientists had speculated that the Martian poles were covered by frozen carbon dioxide. It was not until 2003 that scientists decided that the poles were frozen water with a seasonal layer of frozen carbon dioxide.
Reporting in the February 14, 2003 issue of the journal Science, Caltech planetary science professor Andy Ingersoll presented evidence that the decades old model of the polar caps being made of dry ice was in error.
On Earth, large ice sheets, once they are formed, are shaped mainly by ice and water flow. According to this latest research, other forces have shaped, and continue to shape, polar ice caps on far dryer Mars.
The northern ice cap is a stack of ice and dust layers up to two miles 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 Earth's Grand Canyon but deeper and wider. Some scientists believed the 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 carved the canyon out of a dome of ice.
Other enigmatic features of the ice cap are troughs that spiral outward from the center like a gigantic pinwheel. Since the troughs were discovered in 1972, scientists have proposed several hypotheses about how they formed. Perhaps as Mars spins, ice closer to the poles moves slower than ice farther away, causing the semi-fluid ice to crack. Perhaps, as one mathematical model suggests, increased solar heating in certain areas and heat conduction could cause the troughs to be formed.
Data from Mars now points to both the canyon and spiral troughs as being created and shaped primarily by the wind. Rather than being cut into existing ice very recently, the features formed over millions of years as the ice sheets grew. The shape of the underlying terrain then shaped the troughs and the chasms.
"These anomalous features have gone unexplained for 40 years because we have not been able to see what lies beneath the surface," said Roberto Seu, Shallow Radar team leader at the University of Rome.
Effectively the Martian polar caps are giant sculpted ice/snow dunes. On Earth in the desert such dunes are transitory because they are not cemented/frozen together. On Mars, the ice caps are slower to change but the power of the wind is strong and relentless.
For further information: http://www.jpl.nasa.gov/news/news.cfm?release=2010-180&rn=news.xml&rst=2615