Colliding Atmospheres: Mars vs Comet Siding Spring   
       
   August 12, 2014:  On October 19, 2014, Comet Siding Spring will pass by Mars   
   only 132,000 km away--which would be like a comet passing about 1/3 of the   
   distance between Earth and the Moon.   
       
   The nucleus of the comet won't hit Mars, but there could be a different kind   
   of collision.   
       
   "We hope to witness two atmospheres colliding," explains David Brain of the   
   University of Colorado's Laboratory for Atmospheric and Space Physics (LASP).    
   "This is a once in a lifetime event!"   
       
   https://www.youtube.com/watch?v=2R4yj7DtQbM&feature=youtu.be   
       
   A new ScienceCast video examines what might happen if the atmosphere of Comet   
   Siding Spring hits the atmosphere of Mars.  Play it   
       
   Everyone knows that planets have atmospheres.  Lesser known is that comets do,   
   too.  The atmosphere of a comet, called its "coma," is made of gas and dust   
   that spew out of the sun-warmed nucleus.  The atmosphere of a typical comet is   
   wider than Jupiter.   
       
   "It is possible," says Brain, "that the atmosphere of the comet will interact   
   with the atmosphere of Mars.  This could lead to some remarkable   
   effects-including Martian auroras."   
       
   The timing could scarcely be better.  Just last year, NASA launched a   
   spacecraft named MAVEN to study the upper atmosphere of Mars, and it will be   
   arriving in Sept. 2014 barely a month before the comet.   
       
   MAVEN is on a mission to solve a longstanding mystery: What happened to the   
   atmosphere of Mars?  Billions of years ago, Mars had a substantial atmosphere   
   that blanketed the planet, keeping Mars warm and sustaining liquid water on   
   its surface. Today, only a wispy shroud of CO2 remains, and the planet below   
   is colder and dryer than any desert on Earth. Theories for this planetary   
   catastrophe center on erosion of the atmosphere by solar wind.   
       
   "The goal of the MAVEN mission is to understand how external stimuli affect   
   the atmosphere of Mars," says Bruce Jakosky of LASP, MAVEN's principal   
   investigator. "Of course, when we planned the mission, we were thinking about   
   the sun and the solar wind.  But Comet Siding Spring represents an opportunity   
   to observe a natural experiment, in which a perturbation is applied and we can   
   see the response."   
       
   http://www.nasa.gov/mission_pages/maven/main/#.U-lkt2MYmsM   
       
   Click to visit the MAVEN home pageBrain, who is a member of the MAVEN science   
   team, thinks the comet could spark Martian auroras. Unlike Earth, which has a   
   global magnetic field that shields our entire planet, Mars has a patchwork of   
   "magnetic umbrellas" that sprout out of the surface in hundreds of places all   
   around the planet.  If Martian auroras occur, they would appear in the   
   canopies of these magnetic umbrellas.   
       
   "That is one thing that we will be looking for with both MAVEN and Hubble   
   Space Telescope," says Brain.  "Any auroras we see will not only be neat, but   
   also very useful as a diagnostic tool for how the comet and the Martian   
   atmosphere have interacted."   
       
   The atmosphere of the comet includes not only streamers of gas, but also dust   
   and other debris blowing off the nucleus at 56 kilometers per second relative   
   to Mars.  At that velocity, even particles as small as half a millimeter   
   across could damage spacecraft.  NASA's fleet of Mars orbiters including   
   MAVEN, Mars Odyssey and Mars Reconnaissance Orbiter will maneuver to put the   
   body of Mars between themselves and the comet's debris during the dustiest   
   part of the encounter.   
       
   "It's not yet clear whether any significant dust or gas will hit the Mars   
   atmosphere," cautions Jakosky. "But if it does, it would have the greatest   
   effects on the upper atmosphere."   
       
   Meteoroids disintegrating would deposit heat and temporarily alter the   
   chemistry of upper air layers.  The mixing of cometary and Martian gases could   
   have further unpredictable effects. Although MAVEN, having just arrived at   
   Mars, will still be in a commissioning phase, it will use its full suite of   
   instruments to monitor the Martian atmosphere for changes.   
       
   "By observing both before and after, we hope to determine what effects the   
   comet dust and gas have on Mars, if any," says Jakosky.   
       
   Whatever happens, MAVEN will have a ringside seat.   
       
   Credits:   
   Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.99   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)