TEMPE, ARIZONA Hope springs eternal for life on Mars. And new research shows that it is likely that water springs up from shallow aquifers to shape gully-like features found on the red planet.
Images taken by the Mars Global Surveyor show clear evidence of gully landforms. But what caused the features has been hotly debated.
There are those who see a tie to liquid water bubbling up from subsurface. Some researchers concede that the gullies were formed by liquid water, but from dissipating snowpacks or melting ground ice. Others have speculated that erosive forces, such as wind or liquid carbon dioxide have gouged out the features.
A study team has taken a hard look at over 100 Mars Global Surveyor images containing clear evidence of gully landforms. Their conclusion: water from shallow aquifers remains the most viable theory. They presented their data here at the NASA Astrobiology Institute General Meeting 2003, hosted by Arizona State University.
Merging theory with data
Jennifer Heldmann and Michael Mellon have studied the gullies on the Mars investigation, both of the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder.
Not only were photos used in their assessment. Images were combined with laser altimeter and thermal measurements from Mars Global Surveyor.
"Were merging theory with the data," said Heldmann. "We systematically went through all the proposed models to date, to find out which one matched the observations and those that dont," she told SPACE.com .
"The bottom line is that the shallow aquifer model matches most of the predictions and observations," Heldmann said. "Liquid water is the more likely agent," she said.
Slope orientation
Heldmann said that gullies are spotted on all slope orientations in the region studied: 30 degrees to 72 degrees south. That is, the features can be observed on poleward facing slopes at the extreme high and low latitudes, and are also found on slopes facing the equator in the midrange latitude, she said.
The research team contends that carbon dioxide, melting ground ice, dry landslide, snowmelt, as well as deep aquifers are least likely candidates to form the martian gullies.
The shallow aquifer some 660 to 985 feet (200 to 300 meters) below surface remains as the most viable contender for shaping the gullies.
Recent origin
When did the gullies form?
"It could range from yesterday to 10 million years ago, which in geologic time is still very recent," Heldmann said. Furthermore, the water that flows from the aquifer could be pure not some sort of salty brine.
"We dont see salt deposits at the gully sites. But even if you add salts, then you can depress the freezing point, be in colder places, and still have liquid," Heldmann said.
The gullies are of recent origin, she added, given that they can be seen on top of sand dunes that are transient and changing. Also, most of the gully systems lack impact craters, implying they are very young.
"How young is hard to quantify," Heldmann said. Recent snapshots of the features have not yielded any conclusive data that they are active today, she noted.
Next steps
As for connecting liquid water and Mars life all the requirements are there, Heldmann said. "It could be," is as far as the space scientist would venture.
Although evidence of volcanic activity near the gullies cant be seen, there is the prospect for smaller scale geothermal heating that melts permafrost.
Even without heat, at the depth of the aquifer, temperatures and pressure match to permit liquid water to exist, the researcher said.
Heldmann said a next step would be expanding the search into Mars northern hemisphere. Thermal data supplied by the now-orbiting Mars Odyssey, as well as the Mars Reconnaissance Orbiter in 2005, will greatly add to understanding the gullies on Mars.
"When you go through all the different criteria, water is the one that stands up to all of the different tests that we put it through, based on all the data," Heldmann said. "You dont have to invoke any crazy, radical ideas. It just works out with the data," she concluded.
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