Auroras on Mars   
       
   May 11, 2015:  One day, when humans go to Mars, they might find that,   
   occasionally, the Red Planet has green skies.   
       
   In late Dec. 2014, NASA's MAVEN spacecraft detected evidence of widespread   
   auroras in Mars's northern hemisphere.  The "Christmas Lights," as researchers   
   called them, circled the globe and descended so close to the Martian equator   
   that, if the lights had occurred on Earth, they would have been over places   
   like Florida and Texas.   
       
   "It really is amazing," says Nick Schneider who leads MAVEN's Imaging   
   Ultraviolet Spectrograph (IUVS) instrument team at the University of   
   Colorado.  "Auroras on Mars appear to be more wide ranging than we ever   
   imagined."   
       
   http://preview.tinyurl.com/qb3do4t   
       
   A map of MAVEN's Imaging Ultraviolet Spectrograph (IUVS) auroral detections in   
   December 2014 overlaid on Mars' surface. The map shows that the aurora was   
   widespread in the northern hemisphere, not tied to any geographic location.   
   The aurora was detected in all observations during a 5-day period. Credits:   
   University of Colorado   
       
   This isn't the first time a spacecraft has detected auroras on Mars.  Ten   
   years ago, the European Space Agency's Mars Express found an ultraviolet glow   
   coming from "magnetic umbrellas" in the southern hemisphere.   
       
   Unlike Earth, Mars does not have a global magnetic field that envelops the   
   entire planet.  Instead, Mars has umbrella-shaped magnetic fields that sprout   
   out of the ground like mushrooms, here and there, but mainly in the southern   
   hemisphere.  These umbrellas are remnants of an ancient global field that   
   decayed billions of years ago.   
       
   "The canopies of the patchwork umbrellas are where we expect to find Martian   
   auroras," says Schneider. "But MAVEN is seeing them outside these umbrellas,   
   so this is something new."   
       
   Auroras occur, both on Earth and Mars, when energetic particles from space   
   rain down on the upper atmosphere.  On Earth, these particles are guided   
   toward the poles by our planet's global magnetic field.  That's why auroras   
   are seen most often around the Arctic and Antarctic. On Mars, there is no   
   organized planetary magnetic field to guide the particles north and south-so   
   they can go anywhere.   
       
   "The particles seem to precipitate into the atmosphere anywhere they want,"   
   says Schneider. "Magnetic fields in the solar wind drape across Mars, even   
   into the atmosphere, and the charged particles just follow those field lines   
   down into the atmosphere."   
       
   According to the MAVEN data, solar particles that caused the "Christmas   
   lights" penetrated deeply into the Martian atmosphere---sparking auroras less   
   than 100 km from the surface.  That's lower than auroras on Earth, which range   
   from 100 km to 500 km high.   
       
   Like Mars Express 10 years ago, MAVEN has an ultraviolet camera, so it is not   
   seeing the same thing as human eyes.  What would a human see?   
       
   Schneider isn't certain. "We're still doing the physics," he says, "but we   
   have some educated guesses."   
       
   Although the Martian atmosphere is primarily CO2, it does contain some   
   oxygen--and that is key to the color of the auroras. Excited oxygen atoms in   
   the Martian atmosphere would likely produce green light.   
       
   "A diffuse green glow seems quite possible in the Mars sky, at least when the   
   Sun is throwing off energetic particles," says Schneider.   
       
   MAVEN arrived at Mars in Sept. 2014 on a mission to investigate a planetary   
   mystery:  Billions of years ago, Mars was blanketed by layer of air massive   
   enough to warm the planet and allow liquid water to flow on its surface. Life   
   could have thrived in such an environment. Today, however, only a tiny   
   fraction of that ancient air remains, leaving Mars a desiccated wasteland.   
       
   Where did the Martian atmosphere go?  A favorite theory is solar wind   
   erosion.  Because Mars no longer has a global magnetic field to protect it,   
   solar wind might strip away material from the upper layers of the atmosphere.   
   Watching the auroras could help MAVEN mission scientists learn more about this   
   process.   
       
   "Plus," says Schneider, who is looking forward to future data, "I just love   
   auroras."   
       
   Credits:   
   Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.99   
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