By Leonard David

Senior space writer

updated 7:58 p.m. ET Nov. 13, 2006

Thanks to a flotilla of Mars orbiters, there’s been a steady flow of information streaming in from that puzzling world. Scientists are piecing together a far more coherent view of “real time” versus “geological time” in dealing with the whole of Mars today.

One of the more perplexing finds on Mars are features that look like the product of groundwater seeping to the surface. These gullies could be formed by flowing water — perhaps fed by a groundwater supply. Deposits of soil and rocks transported by these flows have been found, too.

More importantly, gully features appear to be young. So young, in fact, they might be forming today. Clearly, gullies may well be areas of astrobiologial interest — a niche for life that could be present and accounted for on Mars.

It was back in June 2000 when Mars gullies became big news — new landforms that had never been seen before, as revealed in images taken from the Mars Global Surveyor. Spacecraft have now been sending back views of the planet and its ever-changing face over the course of the past five Martian years.

Mars gullies remain controversial as to how they are created. But now gully-watching scientists are nearing a watershed moment in unraveling the story behind the formations.

Mars, by gully
Gullies are high on a “change detection” target list for NASA’s newly positioned Mars Reconnaissance Orbiter, or MRO. Onboard that Mars-circling craft is the ultra-powerful High Resolution Imaging Science Experiment camera, known as HiRISE.

“HiRISE can do an excellent job of change detection due to the high resolution” and other attributes of the imaging system, said Alfred McEwen, director of the Planetary Image Research Lab at the University of Arizona in Tucson. He is MRO’s HiRISE principal investigator.

“We are planning a major effort for change detection over many terrains on Mars,” McEwen told Space.com, such as polar layered deposits, dunes and gullies.

MRO’s point-and-shoot skills also enable reimaging of terrains at the exact same season of different Martian years to match illumination angles.

“Viewing angles will differ, but we plan to acquire stereo images and produce digital elevation models of any site that shows evidence for change ... so we can correct for any viewing effects and make precise measurements of changes,” McEwen noted.

“We will of course see changes in color and albedo [variations in the amount of sunlight reflected by the Martian surface], but interpretation of such surficial changes can be controversial,” McEwen said. “So our hope is to detect and measure actual changes in the topography.” 

Therefore, MRO can constrain the current rates of change of features, McEwen added, like the age of younger features such as gullies — even if the spacecraft and Mars investigators don’t actually spot new gully erosion.

Research focus
The true nature of the Mars gullies remains a work in progress, said Linda Martel, a geologist and an educational outreach staffer at the Hawaii Institute of Geophysics and Planetology at the University of Hawaii.

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“Most researchers are still favoring two models of formation for gullies on Martian slopes — erosion caused by groundwater discharge or by the melting of near-surface ice or snow,” Martel advised.

Mapping the locations and orientations of gullies continues, with Mars scientists looking at temperature and pressure conditions in the subsurface that allow liquid water to exist where gully recesses are found. Also, they are evaluating atmospheric conditions and exposure of the surface to Martian sunshine.

“They are coming up with very convincing reasons why either model makes sense,” Martel said. “But when researchers say that gullies are recent they aren’t talking about today, right now.”

For one, Martel said, it’s impossible to carve the larger gullies — the ones that are about 4 miles (7 kilometers) long — by flowing pure water across the surface under today’s temperature and pressure conditions on Mars. An ongoing research focus, she said, is appreciating what the gullies say about changes in the stability of water or changes in atmospheric pressure, temperature, humidity or exposure to sunshine on Mars.

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