New Gully Deposit in a Crater in the Centauri Montes Region [CREDIT: NASA]
Finally! NASA released images yesterday that provide the best evidence yet that liquid water may still occasionally flow on the Martian surface. Finding evidence for water has been the driving force behind Mars exploration in the last decade because liquid water helps optimistic Earthlings maintain a slim hope for life on the red planet.
A camera on board NASA’s Mars Global Surveyor mission photographed new, light-colored deposits that did not appear in earlier photos of a gully taken in 1999. Scientists used the Mars Orbiter Camera to take multiple pictures to make sure the apparent deposit was not just a lighting trick.
The finding will likely be the crowning achievement for the mission, which was launched a decade ago. The ability to repeatedly photograph promising areas with high resolution gave researchers the chance to search for recent changes in what we had thought was a relatively inactive surface.
In the past, photographs have revealed gullies and other features that appeared to be forged by liquid flow. I was always skeptical, however, that the features could only be due to liquid water. I was not alone, and scientists have considered everything from solid flow to other liquids. NASA addresses some
of these possibilities.
Since their discovery early during the Mars Global Surveyor’s Mars Orbiter Camera investigation, as first reported in June 2000, Martian gullies have presented a puzzle for the Mars science community: what fluid was responsible for the erosion that created the channels, and where did it come from? The gullies seem to be quite young in a geologic sense (millions of years or less), yet modern and geologically-recent Mars is an extremely dry place, where water ice sublimates directly to gas when the temperature is warm enough.
Since June 2000, many hypotheses have been discussed at scientific meetings, in the scientific journals and elsewhere. The original June 2000 hypothesis held that the fluid was liquid water (either pure, salty, acidic, etc.) that came to the surface where slopes intersected conduits of groundwater. Such slopes include crater walls, valley walls, hills, massifs and crater central peaks. Later investigators explored the possibility that rather than liquid groundwater, the source was ground ice, which, under some climate conditions, melted to produce liquid runoff. Still others noted that thick mantles covered a fraction of the gully-bearing slopes, suggesting that the mantles were ancient, dust-covered snow or ice packs that might melt at the base to make liquid water runoff. Water was not the only fluid considered by various colleagues; carbon dioxide can be fluid at some pressures and temperatures. Fluid carbon dioxide was also proposed as a candidate fluidizing agent. Even dry mass movement, or land sliding, of unconsolidated granular material can exhibit some fluid-like behavior. Such mass movements were considered as an explanation for the gullies.
The evidence in this case looks much better for liquid water. The idea that it harbors microbial life, however, is much less certain. But even if Mars is dead, finding liquid water would be great, because its presence might be the deciding factor on whether NASA manages to get a manned trip off the ground (but they would also need to solve the radiation problem).
The New York Times presented more evidence for why the light deposit was caused by water.
Kenneth Edgett, another scientist with Mr. Malin’s company, said that whenever the surface of Mars was disturbed by spacecraft on the ground or by strikes from space rocks, it appeared as a dark color. The light tone of the material in the flow patterns suggests that it came from minerals or other chemicals that were in the water, he said.
“The bright features persist for several years,” Mr. Edgett said, “which means it’s not likely to be frost and is likely to be sediment from water flow.”
I would like to see NASA send a drilling probe to the sight of the gully and confirm the liquid responsible for the flow. Although, some missions drag on for years, NASA is capable of fast-tracking missions for important follow up. But I won’t be holding my breath for results from “future missions” until I hear some specifics.
“These fresh deposits suggest that at some places and times on present-day Mars, liquid water is emerging from beneath the ground and briefly flowing down the slopes. This possibility raises questions about how the water would stay melted below ground, how widespread it might be, and whether there’s a below-ground wet habitat conducive to life. Future missions may provide the answers,” said Malin.
(Full NASA Text)