Here’s an animated gif showing the features of interest.
This series of images shows warm-season features that might be evidence of salty liquid water active on Mars today. Evidence for that possible interpretation is presented in a report by McEwen et al. in the Aug. 5, 2011, edition of Science.
These images come from observations of Newton crater, at 41.6 degrees south latitude, 202.3 degrees east longitude, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter. In time, the series spans from early spring of one Mars year to mid-summer of the following year. The images have been adjusted to correct those taken from oblique angles to show how the scene would look from directly overhead.
The features that extend down the slope during warm seasons are called recurring slope lineae. They are narrow (one-half to five yards or meters wide), relatively dark markings on steep (25 to 40 degree) slopes at several southern hemisphere locations. Repeat imaging by HiRISE shows the features appear and incrementally grow during warm seasons and fade in cold seasons. They extend downslope from bedrock outcrops, often associated with small channels, and hundreds of them form in rare locations. They appear and lengthen in the southern spring and summer from 48 degrees to 32 degrees south latitudes favoring equator-facing slopes. These times and places have peak surface temperatures from about 10 degrees below zero Fahrenheit to 80 degree above zero Fahrenheit (about 250 to 300 Kelvin). Liquid brines near the surface might explain this activity, but the exact mechanism and source of the water are not understood.
“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 Mars Reconnaissance Orbiter Project Scientist Richard Zurek of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Repeated observations show they extend ever farther downhill with time during the warm season.”
And where there’s water, carbon and energy…
As the BBC report adds
“This could be the first flowing water,” said Professor McEwen. This has profound implications in the search for extraterrestrial life.
“Liquid water is absolutely essential for life, and we’ve found life on Earth in pretty much every moist niche,” said Dr Lewis Dartnell, astrobiologist at University College London, who was not involved in the study.
“So perhaps there could be hardy microbes surviving in these short periods of summer meltwater on the desert surface of Mars.”
For geologist Joe Levy of Portland State University, a specialist in Antarctic desert ecosystems, who did not contribute to this work, they represent “a truly tantalising astrobiological target”.
These small and mysterious tendrils could then be the best place to look for Martian life. Professor McEwen says that “for present-day life, these are the most accessible sites”.