Observations from NASA’s Mars Reconnaissance Orbiter (MRO) have revealed possible flowing water during the warmest months on Mars.
“NASA’s Mars Exploration Program keeps bringing us closer to determining whether the Red Planet could harbor life in some form,” NASA administrator Charles Bolden said, “and it reaffirms Mars as an important future destination for human exploration.”
Dark, finger-like features appear and extend down some Martian slopes during late spring through summer, fade in winter, and return during the next spring.
Repeated observations have tracked the seasonal changes in these recurring features on several steep slopes in the middle latitudes of Mars’ southern hemisphere.[ Also Read: Can Twitter Cover Moon, Mars and Jupiter? ]
“The best explanation for these observations so far is the flow of briny water,” said Alfred McEwen of the University of Arizona, Tucson.
McEwen is the principal investigator for the orbiter’s High Resolution Imaging Science Experiment (HiRISE) and lead author of a report about the recurring flows published in Thursday’s edition of the journal Science.
Some aspects of the observations still puzzle researchers, but flows of liquid brine fit the features’ characteristics better than alternate hypotheses. Saltiness lowers the freezing temperature of water.
Sites with active flows get warm enough, even in the shallow subsurface, to sustain liquid water that is about as salty as Earth’s oceans, while pure water would freeze at the observed temperatures.
“These dark lineations are different from other types of features on Martian slopes,” said MRO project scientist Richard Zurek of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Repeated observations show they extend even farther downhill with time during the warm season.”
When researchers checked flow-marked slopes with the orbiter’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), no sign of water appeared. The features may quickly dry on the surface or could be shallow subsurface flows.
“The flows are not dark because of being wet,” McEwen said. “They are dark for some other reason.”
A flow initiated by briny water could rearrange grains or change surface roughness in a way that darkens the appearance. How the features brighten again when temperatures drop is harder to explain.
“It’s a mystery now, but I think it’s a solvable mystery with further observations and laboratory experiments,” McEwen said.
Photo courtesy: NASA