causing surrounding ionized matter to ring like a bell.
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