The Voyager 1 and 2 spacecraft are continuing to deliver incredible data decades after their primary mission of studying the giant planets ended. They are the only human-made objects to have reached interstellar space, providing humanity with observations like no other instrument.
In a new paper published in The Astronomical Journal, researchers have discovered bursts of electrons being accelerated as waves from the Sun encounter the interstellar medium. These electrons are moving at almost the speed of light and were 670 times faster than the shockwaves that created them.
It all starts with the Sun. When our star is active it can throw plasma into the Solar System in spectacular coronal mass ejections moving at hundreds (and sometimes up to thousands) of kilometers per second. These waves of plasma eventually reach interstellar space where they slam into the electrons released by other stars. These electrons are reflected back into interstellar space following magnetic lines.
"What we see here specifically is a certain mechanism whereby when the shock wave first contacts the interstellar magnetic field lines passing through the spacecraft, it reflects and accelerates some of the cosmic ray electrons," lead author Don Gurnett, a professor emeritus in physics and astronomy at Iowa University, said in a statement. "We have identified through the cosmic ray instruments these are electrons that were reflected and accelerated by interstellar shocks propagating outward from energetic solar events at the sun. That is a new mechanism."
The first proposal of this mechanism was put forward in 2014. At the time, Voyager 1 had been traveling in interstellar space for two years and Voyager 2 was still on this side of the boundary.
"The idea that shock waves accelerate particles is not new," Gurnett added. "It all has to do with how it works, the mechanism. And the fact we detected it in a new realm, the interstellar medium, which is much different than in the solar wind where similar processes have been observed. No one has seen it with an interstellar shock wave, in a whole new pristine medium."
It takes radio signals 21 hours to reach Voyager 1 and 17.5 hours to reach Voyager 2. Over the years, some of their instruments had to be switched off to keep them going and Voyager 2 had to go without contact for 8 months this year. Despite all this, they endure and continue to send back data from the depths of space.