NASA’s Voyager 2 spacecraft has entered interstellar space, the second man-made object to do so. 18 billion km from Earth, it left the safety of the heliosphere – a bubble of particles and magnetic fields created by the Sun – on 5 November 2018, it was announced today.
According to Voyager 2’s plasma instruments, there was a sharp decline in the speed of the solar wind on 5 November 2018, indicating the probe had crossed the heliopause – the boundary between the Solar System and interstellar space.
Voyager 1 crossed this boundary in 2012, heading out of the Solar System after completing its flybys of Jupiter and Saturn.
However, Voyager 2 took the scenic route, swinging by Uranus and Neptune before heading out, and has taken 6 years catching up.
Researchers are particularly enthused about the milestone as Voyager 2 still has a working Plasma Science Experiment instrument (PLS) – Voyager 1’s stopped working in 1980, long before it crossed into interstellar space.
While in the solar bubble, the PLS measured the solar wind’s speed, density and temperature. It will now do the same for the interstellar wind.
“Working on Voyager makes me feel like an explorer, because everything we’re seeing is new,” says John Richardson, PLS’s principal investigator, from MIT.
“Even though Voyager 1 crossed the heliopause in 2012, it did so at a different place and a different time, and without the PLS data. So we’re still seeing things that no one has seen before.”
NASA launched the Voyager missions 41 years ago in 1977.
They pair were originally intended to only visit Jupiter and Saturn, but the mission was such a success it was expanded to the outer Solar System and beyond.
Time is now running short as the probes’ power supplies runs down, though the team hopes to celebrate the mission’s 50th anniversary.
In the meantime, Voyager’s operators are strategically turning off systems to keep the spacecraft running and sending back data from a region no man-made object has been before.
“I think we’re all happy and relieved that the Voyager probes have both operated long enough to make it past this milestone,” said Suzanne Dodd, Voyager project manager at NASA’s Jet Propulsion Laboratory.
“This is what we’ve all been waiting for.
Now we’re looking forward to what we’ll be able to learn from having both probes outside the heliopause.”