"Slam Dunk" Sign of Ancient Water on Mars   
       
   Dec 8, 2011:  NASA's Mars rover Opportunity has found bright veins of a   
   mineral, apparently gypsum, deposited by water near the rim of Endeavour   
   Crater. The discovery was presented yesterday at the American Geophysical   
   Union's conference in San Francisco.   
       
   "This tells a slam-dunk story that water flowed through underground fractures   
   in the rock," said Steve Squyres of Cornell University, Ithaca, N.Y.,   
   principal investigator for Opportunity. "This stuff is a fairly pure chemical   
   deposit that formed in place right where we see it.1 It's the kind of thing   
   that makes geologists jump out of their chairs."   
       
   http://www.nasa.gov/mission_pages/mer/multimedia/pia15033.html   
       
   This color view of a mineral vein called "Homestake" comes from Opportunity's   
   panoramic camera. Opportunity examined it in November 2011 and found it to be   
   rich in calcium and sulfur, possibly the calcium-sulfate mineral gypsum.   
   [larger image]   
       
   The vein examined most closely by Opportunity is about the width of a human   
   thumb (1 to 2 centimeters) and 40 to 50 centimeters long. Observations by the   
   rover reveal this vein and others like it within an apron surrounding the rim   
   of Endeavour Crater. Nothing like it was seen in the 33 kilometers of   
   crater-pocked plains that Opportunity explored for 90 months before it reached   
   Endeavour, nor in the higher ground of the crater's rim.2   
       
   Last month, researchers used the Microscopic Imager and Alpha Particle X-ray   
   Spectrometer on the rover's arm and multiple filters of the Panoramic Camera   
   on the rover's mast to examine the vein, which is informally named   
   "Homestake."  The spectrometer identified plentiful calcium and sulfur, in a   
   ratio pointing to relatively pure calcium sulfate.   
       
   Calcium sulfate can exist in many forms  varying by how much water is bound   
   into the minerals' crystalline structure. The multi-filter data from the   
   camera suggest gypsum, a hydrated calcium sulfate. On Earth, gypsum is used   
   for making drywall and plaster of Paris.   
       
   Observations from orbit had detected gypsum on Mars previously. A dune field   
   of windblown gypsum on far northern Mars resembles the glistening gypsum dunes   
   in White Sands National Monument in New Mexico. The origin of that windblown   
   gypsum is, however, uncertain.   
       
   "It is a mystery where gypsum sand on northern Mars comes from," said   
   Opportunity science-team member Benton Clark of the Space Science Institute in   
   Boulder, Colo. "At Homestake, however, we see the mineral right where it   
   formed. It will be important to see if there are deposits like this in other   
   areas of Mars."   
       
   http://www.nasa.gov/mission_pages/mer/multimedia/pia15035.html   
       
   A microscopic image of the "Homestake" mineral vein. [larger image] The   
   Homestake deposit, whether gypsum or another form of calcium sulfate, likely   
   formed from water dissolving calcium out of volcanic rocks. The calcium   
   combined with sulfur that was either leached from the rocks or introduced as   
   volcanic gas, and it was deposited as calcium sulfate into an underground   
   fracture that later became exposed at the surface.   
       
   The discovery of gypsum fits the emerging picture of an ancient wet   
   environment.  Throughout Opportunity's long traverse across Mars' Meridiani   
   plain, the rover has driven over bedrock composed of magnesium, iron and   
   calcium sulfate minerals that also indicate the presence of water billions of   
   years ago. The highly concentrated calcium sulfate at Homestake could have   
   been produced in conditions more neutral than the harshly acidic conditions   
   indicated by the other sulfate deposits observed by Opportunity.   
       
   "It could have formed in a different type of water environment, one more   
   hospitable for a larger variety of living organisms," Clark said.   
       
   Opportunity has been exploring Mars for nearly 8 years, far exceeding than the   
   rover's original 3-month mission, which began in 2004.  Gypsum veins are just   
   the latest example of an important discovery about wet environments on ancient   
   Mars that may have been favorable for supporting microbial life. Opportunity's   
   equally productive twin, Spirit,  stopped communicating in 2010. Opportunity   
   continues exploring, currently heading to a sun-facing slope on the northern   
   end of the Endeavour rim fragment called "Cape York" to keep its solar panels   
   at a favorable angle during the mission's fifth Martian winter.   
       
   For more information about the rovers, including NASA's newest rover Curiosity   
   now en route to Mars, visit http://www.nasa.gov/rovers and http:   
   /marsrovers.jpl.nasa.gov .   
       
   Production Editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   NASA Mars Rover Finds Mineral Vein Deposited by Water --more images and   
   inforation related to this story   
       
   Mars Exploration Rovers -- home page   
       
   Footnotes:   
       
   (1) The fact that the gypsum is found where right it formed is significant.   
   "That can't be said for other gypsum seen on Mars or for other water-related   
   minerals Opportunity has found," notes Squyres. Other deposits of gypsum on   
   Mars, for instance, are windblown dune formations where the mineral might have   
   traveled far from its point of origin.   
       
   (2) Homestake and similar-looking veins appear in a zone where the   
   sulfate-rich sedimentary bedrock of the plains meets older, volcanic bedrock   
   exposed at the rim of Endeavour. That location may offer a clue about their   
   origin. "We want to understand why these veins are in the apron but not out on   
   the plains," said the mission's deputy principal investigator, Ray Arvidson,   
   of Washington University in St. Louis. "The answer may be that rising   
   groundwater coming from the ancient crust moved through material adjacent to   
   Cape York and deposited gypsum, because this material would be relatively   
   insoluble compared with either magnesium or iron sulfates."   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.64   
    * Origin: NCS BBS (1:3828/7)