Salt Water May Flow on Mars   
       
   August 4, 2011: Observations from NASA's Mars Reconnaissance Orbiter have   
   revealed possible flowing water during the warmest months on Mars.   
       
   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.   
       
   "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.   
       
   Copy the link below into your browser to view a movie of 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. [movie]   
       
   http://www.nasa.gov/mission_pages/MRO/multimedia/pia14472.html   
       
   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."   
       
   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 than previously reported   
   gullies on Martian slopes. However, some of those locations display more than   
   1,000 individual flows. Also, while gullies are abundant on cold, pole-facing   
   slopes, these dark flows are on warmer, equator-facing slopes.   
       
   The images show flows lengthen and darken on rocky equator-facing slopes from   
   late spring to early fall. The seasonality, latitude distribution and   
   brightness changes suggest a volatile material is involved, but there is no   
   direct detection of one. The settings are too warm for carbon-dioxide frost   
   and, at some sites, too cold for pure water. This suggests the action of   
   brines, which have lower freezing points. Salt deposits over much of Mars   
   indicate brines were abundant in Mars' past. These recent observations suggest   
   brines still may form near the surface today in limited times and places.   
       
   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.   
   [...]   
   Blue squares on this map of Mars mark the locations of possible briny-flow   
   features. [more] "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.   
       
   These results are the closest scientists have come to finding evidence of   
   liquid water on the planet's surface today. Frozen water, however has been   
   detected near the surface in many middle to high-latitude regions.   
   Fresh-looking gullies suggest slope movements in geologically recent times,   
   perhaps aided by water. Purported droplets of brine also appeared on struts of   
   the Phoenix Mars Lander. If further study of the recurring dark flows supports   
   evidence of brines, these could be the first known Martian locations with   
   liquid water.   
       
   "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."   
       
   For more information about the Mars Reconnaissance Orbiter, visit:   
   http://www.nasa.gov/mro and http://marsprogram.jpl.nasa.gov/mro/ .   
       
       
   Production editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
       
   Credits: The Mars Reconnaissance Orbiter is managed by JPL for NASA's Science   
   Mission Directorate in Washington. The University of Arizona's Lunar and   
   Planetary Laboratory operates HiRISE. The camera was built by Ball Aerospace &   
   Technologies Corp. in Boulder, Colo. Johns Hopkins University Applied Physics   
   Laboratory in Laurel, Md., provided and operates CRISM. JPL is a division of   
   the California Institute of Technology in Pasadena.   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.64   
    * Origin: NCS BBS (1:3828/7)