Inside the heliosphere, the solar wind prevails, a high-energy plasma that streams from the sun's corona into space, and which is made up of stripped bits of atoms, like electrons, protons, and alpha particles.
Teams at the CSIRO's Parkes radio telescope and the Canberra Deep Space Communication Complex combined forces so NASA could collect as much information as possible from the spacecraft which, while still mostly in working order after being launched in 1977, can no longer record data. "We had left the bubble basically". Their continuing science will help shed light on how particles flowing off the sun collide with the particles on the interstellar wind beyond.
As they traveled further into space, the gap between them grew, each taking different paths on their way out to eternity.
With both Voyager 1 and Voyager 2 beyond the heliopause, scientists are eager to combine those measurements with those from spacecraft and instruments within the sun's heliosphere. Dodd said that her own goal for the mission is to coax a full 50 years of exploration out of the spacecraft since their launch in 1977. Fluctuating solar activity made the boundary oscillate, so the spacecraft ended up crossing the termination shock several times. "Our studies start at the sun and extend out to everything the solar wind touches".
Unlike Voyager 1, Voyager 2 has instruments set up that measure changes in the speed and direction of high energy plasma particles as the wind from our Sun meets the high energy particles streaming in from the rest of the galaxy.
"This is what we've all been waiting for", Suzanne Dodd, NASA's Voyager project manager, said in a statement. "That means we must be in the interstellar medium". This instrument stopped working on Voyager 1 in 1980, but it's still operating on Voyager 2.
Voyager 2 may be freshly interstellar, but it won't be anywhere near another star until 40,000 years from now.
"There is still a lot to learn about the region of interstellar space immediately beyond the heliopause", said Ed Stone in the accompanying NASA/JPL press release. It's trailing Voyager 1, which reached interstellar space in 2012.
Of course, that's a rather long time - particularly when one considers that the Voyager probes are already massive overachievers when it comes to longevity. These include the instrument's principal investigator, John Richardson, a principal research scientist in the MIT Kavli Institute for Astrophysics and Space Research, and John Belcher, the Class of 1992 Professor of Physics.
This Nasa artist's concept shows the general locations of Nasa's two Voyager spacecraft, Voyager 1 (top) has sailed beyond our solar bubble into interstellar space, the space between stars, and Voyager 2 (bottom) is still exploring the outer layer of the solar bubble.