Post by Chicago Astronomer - Astro Joe on Apr 23, 2010 1:44:53 GMT -6
Widening gullies on Mars point to liquid water
From COSMOS:
WASHINGTON, D.C.: Changes in gullies on Mars suggest that there is flowing water on the red planet, scientists said.
Martian gullies carved into hill slopes and the walls of impact craters were discovered several years ago. On Earth, gullies usually form through the action of liquid water – long thought to be absent on the Martian surface because the temperature and atmospheric pressure were believed to be too low.
But direct observation tells a different story, according to research published in Geophysical Research Letters released by the American Geophysical Union.
Melting of small amounts of ice
Using high resolution imaging to look at the planet's surface, Dennis Reiss, a geologist at Westfaelische Wilhelms University in Muenster, Germany and his team of researchers, observed that from November of 2006 to May of 2009, a two-meter-wide gully had grown in length by 50 meters in one year and by 120 meters the following year.
"There has been a long debate about what has caused them," said Harold Hiesinger, a geologist at Westfaelische Wilhelms University and a member of Reiss's team.
Though they believe that these changes are best explained by a process of erosion triggered by the melting of small amounts of ice.
Carbon dioxide common explanation
Other researchers argue that such changes could be explained by the presence of carbon dioxide.
"I agree with these authors, and others, that carbon dioxide is very unlikely to be responsible for gullies," said Michael Manga, a geologist at the University of California, Berkeley in an email, explaining that CO2 is a gas and would cause explosions:
"It wouldn't stick with the particles and allow them to keep flowing," he said.
Dry avalanches or wet landslides?
There has been debate on whether water is necessary to create such gullies and some argue that they could've been made by small, dry avalanches.
"But the gullies have levees (ridges) around them and this is characteristic of wet landslides on Earth," Manga said.
Added Taylor Perron, a geologist at Massachusetts Institute of Technology in Cambridge: "The fact that the flows are travelling over such gentle slopes - gentle enough that a flow of dry sand would stop moving due to friction - is strong evidence that they contained a fluid, possibly
water."
There is also speculation on whether the water is from melting of surface or near-surface ice or if it is from deeper aquifers.
Melting ice in mid-Spring
"The latter is hard to reconcile with gullies beginning near the top of slopes," said Manga, suggesting that melting of surface ice as temperatures increase in mid-spring is what is responsible for the lengthening of Mars' gullies.
"These authors show that it does get warm enough to melt near-surface water at the times the gullies form," said Manga.
"The idea that ice condenses during the cold season, and then melts to form gullies, seems reasonable and consistent with the observations."
www.cosmosmagazine.com/news/3410/widening-gullies-mars-point-flowing-water
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I have always advocated for liquid water on Mars, yet the old school know-it-alls were more comfortable with the Cold-Dry-Dead model of current Mars...chiding any suggestions of a wet vibrant Mars.
Funny...I don't hear much from them anymore.