After NASA’s Voyager 1 probe left the solar system back in 2012, its twin satellite was still trailing behind, but now the suspense is on. It seems that Voyager 2 is now also creeping up on interstellar space.
Voyager 2 is currently around about 11 billion miles from our planet—more than 118 times as far as we are from the sun. It has been floating around the fringe of the heliosphere, that enormous bubble of solar material and magnetic fields that surrounds the sun and planets. The spacecraft that refuses to give up has now journeyed to the very edge of that bubble, the heliopause, and is now on the verge of being the second human-made object to go interstellar.
NASA recently found out Voyager 2's location by monitoring data from its Cosmic Ray Subsystem instrument and its Low-Energy Charged Particle instrument. It has beamed back proof of being zapped by 5% more cosmic rays than usual, which might not sound like a huge deal, but cosmic rays are made up of high-velocity particles from beyond the solar system. Meaning, Voyager 2 is getting closer and closer to the final frontier.
Nobody knows how many cosmic rays could potentially be shooting towards the second Voyager because the heliosphere blocks some of them. What Voyager 2 mission planners do expect is that more and more cosmic rays will hit the spacecraft as it gets closer to the heliopause and ultimately flies into wild space. Three months before Voyager 1 crossed the heliopause, the increase in cosmic rays was similar to what Voyager 2 is now experiencing.
The heliopause is dynamic. During the sun’s 11-year cycle, it keeps moving inward and outward as solar flares and coronal mass ejections occur, and whether solar activity spikes or plummets determines its position. Where Voyager 2 is now could be very different from where Voyager 1 was at a comparable point in its journey back in 2012. It is already somewhere entirely different in the heliosheath, or the extreme outer region of the heliosphere, than its twin was around that time. That may or may not be an indication for NASA to expect its exit to happen later than expected.
"We're seeing a change in the environment around Voyager 2, there's no doubt about that," said Voyager Project Scientist Ed Stone. "We're going to learn a lot in the coming months, but we still don't know when we'll reach the heliopause. We're not there yet—that's one thing I can say with confidence."
Whether that generates the same memes Voyager 1 did remains to be seen.