Voyager Buffeted by Interstellar 'Tsunami Waves'   
       
   Dec. 16, 2014:  Since 2012, NASA's Voyager 1 spacecraft has experienced three   
   'tsunami waves' in interstellar space.  The most recent, which reached the   
   spacecraft earlier this year, is still propagating outward according to new   
   data. It is the longest-lasting shock wave that researchers have seen in   
   interstellar space.   
       
   "Most people would have thought the interstellar medium would have been smooth   
   and quiet. But these shock waves seem to be more common than we thought," said   
   Don Gurnett, professor of physics at the University of Iowa in Iowa City.   
   Gurnett presented the new data Monday, Dec. 15 at the American Geophysical   
   Union meeting in San Francisco.   
       
   https://www.youtube.com/watch?v=_u-RZTwpECg#t=41   
       
   The Voyager 1 spacecraft has experienced three "tsunami waves" in interstellar   
   space. Listen to how these waves cause surrounding ionized matter to ring like   
   a bell.   
       
   A "tsunami wave" occurs when the sun emits a coronal mass ejection, throwing   
   out a magnetic cloud of plasma from its surface. This generates a wave of   
   pressure. When the wave runs into the interstellar plasma -- the charged   
   particles found in the space between the stars -- a shock wave results that   
   perturbs the plasma.   
       
   "The tsunami causes the ionized gas that is out there to resonate -- "sing" or   
   vibrate like a bell," said Ed Stone, project scientist for the Voyager mission   
   based at California Institute of Technology in Pasadena.   
       
   This is the third shock wave that Voyager 1 has experienced. The first event   
   was in October to November of 2012, and the second wave in April to May of   
   2013 revealed an even higher plasma density. Voyager 1 detected the most   
   recent event in February, and it is still going on as of November data. The   
   spacecraft has moved outward 250 million miles (400 million kilometers) during   
   the third event.   
       
   "This remarkable event raises questions that will stimulate new studies of the   
   nature of shocks in the interstellar medium," said Leonard Burlaga,   
   astrophysicist emeritus at NASA Goddard Spaceflight Center in Greenbelt,   
   Maryland, who analyzed the magnetic field data that were key to these results.   
       
   It is unclear to researchers what the unusual longevity of this particular   
   wave may mean. They are also uncertain as to how fast the wave is moving or   
   how broad a region it covers.   
       
   The second tsunami wave helped researchers determine in 2013 that Voyager 1   
   had left the heliosphere, the bubble created by the solar wind encompassing   
   the sun and the planets in our solar system. Denser plasma "rings" at a higher   
   frequency, and the medium that Voyager flew through, was 40 times denser than   
   what had been previously measured. This was key to the conclusion that Voyager   
   had entered a frontier where no spacecraft had gone before: interstellar space.   
       
   "The density of the plasma is higher the farther Voyager goes," Stone said.   
   "Is that because the interstellar medium is denser as Voyager moves away from   
   the heliosphere, or is it from the shock wave itself? We don't know yet."   
       
   Gurnett, principal investigator of the plasma wave instrument on Voyager,   
   expects that such shock waves propagate far out into space, perhaps even to   
   twice the distance between the sun and where the spacecraft is right now.   
       
   Voyager 1 and its twin, Voyager 2, were launched 16 days apart in 1977. Both   
   spacecraft flew by Jupiter and Saturn. Voyager 2 also flew by Uranus and   
   Neptune. Voyager 2, launched before Voyager 1, is the longest continuously   
   operated spacecraft and is expected to enter interstellar space in a few years.   
       
   Credits and more information:   
   Production editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   JPL, a division of Caltech, built the twin Voyager spacecraft and operates   
   them for the Heliophysics Division within NASA's Science Mission Directorate   
   in Washington.   
       
   For more information on the Voyager mission, visit http://voyager.jpl.nasa.gov   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.99   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)