August 04, 2011 PASADENA, Calif. -- Observations from NASA's Mars ReconnaissanceOrbiter have revealed possible flowing water during the warmest monthson Mars.

"NASA's Mars Exploration Program keeps bringing us closer todetermining whether the Red Planet could harbor life in some form,"NASA Administrator Charles Bolden said, "and it reaffirms Mars as animportant future destination for human exploration."

Dark, finger-like features appear and extend down some Martian slopesduring late spring through summer, fade in winter, and return duringthe next spring. Repeated observations have tracked the seasonalchanges in these recurring features on several steep slopes in themiddle latitudes of Mars' southern hemisphere.

"The best explanation for these observations so far is the flow ofbriny water," said Alfred McEwen of the University of Arizona, Tucson.McEwen is the principal investigator for the orbiter's High ResolutionImaging Science Experiment (HiRISE) and lead author of a report aboutthe recurring flows published in Thursday's edition of the journalScience.

Some aspects of the observations still puzzle researchers, butflows of liquid brine fit the features' characteristics better thanalternate hypotheses. Saltiness lowers the freezing temperature ofwater. Sites with active flows get warm enough, even in the shallowsubsurface, to sustain liquid water that is about as salty as Earth'soceans, while pure water would freeze at the observed temperatures.

"These dark lineations are different from other types of featureson Martian slopes," said Mars Reconnaissance Orbiter Project ScientistRichard Zurek of NASA's Jet Propulsion Laboratory in Pasadena, Calif."Repeated observations show they extend ever farther downhill with timeduring the warm season."

The features imaged are only about 0.5 to 5 yards or meters wide,with lengths up to hundreds of yards. The width is much narrower thanpreviously reported gullies on Martian slopes. However, some of thoselocations display more than 1,000 individual flows. Also, while gulliesare abundant on cold, pole-facing slopes, these dark flows are onwarmer, equator-facing slopes.

The images show flows lengthen and darken on rocky equator-facingslopes from late spring to early fall. The seasonality, latitudedistribution and brightness changes suggest a volatile material isinvolved, but there is no direct detection of one. The settings are toowarm for carbon-dioxide frost and, at some sites, too cold for purewater. This suggests the action of brines, which have lower freezingpoints. Salt deposits over much of Mars indicate brines were abundantin Mars' past. These recent observations suggest brines still may formnear the surface today in limited times and places.

When researchers checked flow-marked slopes with the orbiter'sCompact Reconnaissance Imaging Spectrometer for Mars (CRISM), no signof water appeared. The features may quickly dry on the surface or couldbe 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 changesurface roughness in a way that darkens the appearance. How thefeatures 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.

These results are the closest scientists have come to findingevidence of liquid water on the planet's surface today. Frozen water,however has been detected near the surface in many middle tohigh-latitude regions. Fresh-looking gullies suggest slope movements ingeologically recent times, perhaps aided by water. Purported dropletsof brine also appeared on struts of the Phoenix Mars Lander. If furtherstudy of the recurring dark flows supports evidence of brines, thesecould be the first known Martian locations with liquid water.

The Mars Reconnaissance Orbiter is managed by JPL for NASA'sScience Mission Directorate in Washington. The University of Arizona'sLunar and Planetary Laboratory operates HiRISE. The camera was built byBall Aerospace & Technologies Corp. in Boulder, Colo. Johns HopkinsUniversity Applied Physics Laboratory in Laurel, Md., provided andoperates CRISM. JPL is a division of the California Institute ofTechnology in Pasadena.

For more information about the Mars Reconnaissance Orbiter, visit: http://www.nasa.gov/mro and http://marsprogram.jpl.nasa.gov/mro/ .

Full Link and with pictures and Slideshows: http://www.jpl.nasa.gov/news/news.cfm?release=2011-242&;cid=release_2011-242&msource=11242&tr=y&auid=8766130