Does liquid water flow on Mars? NASA scientists have built a strong case that it does.
In a press briefing held today, a team of planetary scientists announced that the Mars Reconnaissance Orbiter had observed hundreds of dark, fingerlike streaks running down crater walls that seem to appear and disappear with the Martian seasons. The flows look suspiciously like they're produced by liquid water flowing downslope.
Led by Alfred McEwen (University of Arizona), a team of 10 researchers report in today's Science that MRO's High Resolution Imaging Science Experiment (HiRISE) spotted the flows in a range of temperate latitudes from 32°S to 48°S, usually equator-facing slopes that can reach summertime peaks from -10° to 80°F (-25° to +25°C). They range in size from 0.5 to 5 yards in width and can be hundreds of yards long.
"The observations are definitely intriguing in that they provide the most persuasive evidence yet of the presence of seasonally-active liquid water in the near-subsurface," says Stephen Clifford (Lunar and Planetary Institute), an expert on Martian hydrology.
NASA scientists conjecture that the flows on the crater walls, which tilt up at an angle of 35°, might stem from the periodic melting of briny water located just beneath Mars's surface. Saltwater has a lower freezing point than pure water does and thus would be able to remain liquid at frigid temperatures.
The mid-latitudes where the flows are seen represent a kind of sweet spot, planetary scientists believe. Spacecraft measurements suggest that water ice lies buried just below the surface, yet temperatures are warm enough to melt salt-infused water ice. The scientists do not yet know, though, whether the brine outflows emerge from a central briny pool or from isolated saltwater pockets hidden beneath Mars's ruddy crust.
These flows differ from the gullies found on the walls of other Martian craters. While the gullies run down the colder crater walls that face the poles, the newly found flows face the Sun.
The possible existence of liquid saltwater reservoirs encourages speculation that life on Mars might be able to eke out a meager existence. "The presence of brine might allow for the expression of an active biological process," said Lisa Pratt (Indiana University), a biogeochemist and director of one of NASA's astrobiology teams. None of the data gathered by the Mars Reconnaissance Orbiter, though, suggests the presence of life.
The HiRISE images don't prove that the flows represent leaking subterranean plumbing. In fact, a spectrometer aboard MRO has been unable to confirm that the flows contain water. Further scrutiny from martian orbit is planned, says McEwen, HiRISE's principal investigator, and tests will be carried out in labs here on Earth to try to mimic what was seen by MRO. If those simulations succeed, they'll strengthen the hypothesis that saltwater flows on Mars today.
For more information about this finding, go here.