July 11, 2014
Martian Dry Ice Gullies Formed By Seasonal CO2 Freezing, Not Water
Gerard LeBlond for redOrbit.com - Your Universe Online
NASA’s Mars Reconnaissance Orbiter (MRO) continually makes high-resolution observations of the surface of Mars. Recent images have revealed that the gullies on the surface are mainly formed by seasonal freezing of carbon dioxide and not liquid water. The report has been published online in the journal Icarus.In 2000, the first reports on these gullies suggested the presence of water on Mars created them by erosion, the same way gullies are formed here on Earth. Mars has water vapor as well as frozen water, but liquid water has never been confirmed. Water is essential for sustaining all forms of life.
“As recently as five years ago, I thought the gullies on Mars indicated activity of liquid water. We were able to get many more observations, and as we started to see more activity and pin down the timing of gully formation and change, we saw that the activity occurs in winter,” said lead author Colin Dundas from the US Geological Survey's Astrogeology Science Center in Flagstaff, Arizona.
Dundas, along with co-authors Serina Diniega of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, and Alfred McEwen of the University of Arizona, Tucson, used the High Resolution Imaging Science Experiment (HIRISE) camera on the MRO to examine gullies from 356 different locations on the surface of Mars beginning in 2006. Active gully formation of new channel segments and increased deposits were observed in the downhill side of some gullies at 38 sites.
Dated before-and-after images determined the seasonal carbon dioxide frost and temperatures would prevent the presence of liquid water. Frozen carbon dioxide is commonly known as dry ice. On Earth it does not naturally exist, but on Mars it is common and plentiful.
The dry ice is linked with events like carbon dioxide gas geysers and lines on the sand dunes formed by blocks of dry ice being lubricated by gas to allow the dry material to flow. Another way these gullies and lines can form is the increasing weight of the frost buildup on steep slopes allowing them to slide downward.
Previous theories on these gullies indicate that millions of years ago they were formed when the climate would allow liquid water. However, the new findings indicate current activities are forming these gullies.
“Much of the information we have about gully formation, and other active processes, comes from the longevity of MRO and other orbiters. This allows us to make repeated observation of sites to examine surface changes over time,” said Diniega.
This report indicates gullies are being formed without the presence of liquid water, but other reports within the previous year have indicated possible liquid water flows on Mars.
“I like that Mars can still surprise us. Martian gullies are fascinating features that allow us to investigate a process we just don't see on Earth,” Dundas said.