Collision Course? A Comet Heads for Mars   
       
   March 27, 2013: Over the years, the spacefaring nations of Earth have sent   
   dozens of probes and rovers to explore Mars.  Today there are three active   
   satellites circling the red planet while two rovers, Opportunity and   
   Curiosity, wheel across the red sands below.  Mars is dry, barren, and   
   apparently lifeless.   
       
   Soon, those assets could find themselves exploring a very different kind of   
   world.   
       
   "There is a small but non-negligible chance that Comet 2013 A1 will strike   
   Mars next year in October of 2014," says Don Yeomans of NASA's Near-Earth   
   Object Program at JPL.  "Current solutions put the odds of impact at 1 in   
   2000."   
       
   http://www.youtube.com/watch?v=1T2eBSexgX4   
       
   In a new ScienceCast video, experts discuss what might happen if Comet 2013 A1   
   hits Mars. Play itThe nucleus of the comet is probably 1 to 3 km in diameter,   
   and it is coming in fast, around 56 km/s (125,000 mph). "It if does hit Mars,   
   it would deliver as much energy as 35 million megatons of TNT," estimates   
   Yeomans.   
       
   For comparison, the asteroid strike that ended the dinosaurs on Earth 65   
   million years ago was about three times as powerful, 100 million megatons.   
   Another point of comparison is the meteor that exploded over Chelyabinsk,   
   Russia, in February of 2013, damaging buildings and knocking people down. The   
   Mars comet is packing 80 million times more energy than that relatively puny   
   asteroid.   
       
   An impact wouldn't necessarily mean the end of NASA's Mars program. But it   
   would transform the program-- along with Mars itself.   
       
   "I think of it as a giant climate experiment," says Michael Meyer, lead   
   scientist for the Mars Exploration Program at NASA headquarters.  "An impact   
   would loft a lot of stuff into the Martian atmosphere--dust, sand, water and   
   other debris. The result could be a warmer, wetter Mars than we're accustomed   
   to today."   
       
   Meyer worries that solar-powered Opportunity might have a hard time surviving   
   if the atmosphere became opaque.  Nuclear-powered Curiosity, though, would   
   carry on just fine.  He also notes that Mars orbiters might have trouble   
   seeing the surface, for a while at least, until the debris begins to clear.   
       
   http://www.nasa.gov/multimedia/imagegallery/image_feature_2203.html   
       
   Opportunity might have trouble observing the aftermath of a comet impact if   
   dust in the air cuts sunlight to the rover's solar panels. MoreA direct impact   
   remains unlikely.  Paul Chodas of NASA's Near-Earth Object Program stresses   
   that a 1 in 2000 chance of impact means there's a 1999 in 2000 chance of no   
   impact.  "A near-miss is far more likely," he points out.   
       
   Even a near miss is a potentially big event.  The latest orbit solutions put   
   the comet somewhere within 300,000 km of the red planet at closest aThat means   
   Mars could find itself inside the comet's gassy, dusty atmosphere or "coma."    
   Visually, the comet would reach 0th magnitude, that is, a few times brighter   
   than a 1st magnitude star, as seen from the Red Planet.   
       
   "Cameras on ALL of NASA's spacecraft currently operating at Mars should be   
   able to take photographs of Comet 2013 A1," says Jim Bell, a planetary   
   scientist and Mars imaging specialist at Arizona State University. "The issue   
   with Mars Odyssey and the Mars Reconnaissance Orbiter will be the ability to   
   point them in the right direction; they are used to looking down, not up.   
   Mission designers will have to figure out if that is possible."   
       
   "The issue with the Opportunity and Curiosity rovers will be power for imaging   
   at night," he continues. "Opportunity is solar powered and so would need to   
   dip into reserve battery power to operate the cameras at night. Whether or not   
   we will be able to do this will depend on how much power the rover is getting   
   from dusty solar panels in the daytime. On the other hand, Curiosity is   
   nuclear powered, so it could have better odds at night-time imaging."   
       
   Researchers will be keenly interested to see how the comet's atmosphere   
   interacts with the atmosphere of Mars.  For one thing, there could be a meteor   
   shower. "Analyzing the spectrum of disintegrating meteors could tell us   
   something interesting about the chemistry of the upper atmosphere," notes   
   Meyer.   
       
   http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2013%20A1;orb=1   
       
   Click to view an interactive 3D orbit of Comet 2013 A1. Another possibility is   
   Martian auroras.  Unlike Earth, which has a global magnetic field that wraps   
   around our entire planet, Mars is only magnetized in patches. Here and there,   
   magnetic umbrellas sprout out of the ground, creating a crazy-quilt of   
   magnetic poles concentrated mainly in the southern hemisphere. Ionized gases   
   hitting the top of the Martian atmosphere could spark auroras in the canopies   
   of the magnetic umbrellas.   
       
   Even before the comet flyby was known, NASA had already decided to send a   
   spacecraft to Mars to study the dynamics of the Martian atmosphere. If the   
   probe, named MAVEN (short for "Mars Atmosphere and Volatile Evolution"), is   
   launched on time in November 2013, it would reach Mars just a few weeks before   
   the comet in 2014.   
       
   However, notes MAVEN's principal investigator Bruce Jakosky of the University   
   of Colorado, the spacecraft won't be ready to observe the comet when it   
   reaches Mars.  "It takes a while to get into our science mapping orbit, deploy   
   the booms, turn on and test the science instruments--and so on," he explains.   
   "MAVEN won't be fully operational until perhaps two weeks after the comet   
   passes.  There are some effects that I would expect to linger for a relatively   
   long period--especially if the comet hits Mars--and we will be able to observe   
   those changes."   
       
   Astronomers around the world are monitoring 2013 A1.  Every day, new data   
   arrive to refine the comet's orbit.  As the error bars shrink, Yeomans expects   
   a direct hit to be ruled out.  "The odds favor a flyby, not a collision," he   
   says.   
       
   Either way, this is going to be good. Stay tuned for updates as the comet   
   approaches.   
       
       
   Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.91   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)