The Voyager 2 spacecraft has joined its twin, Voyager 1, in interstellar space, NASA announced on Monday. The two probes, launched in 1977, have travelled farther from Earth than any human-made objects in history.
Voyager scientists pinpointed November 5 as the day that the spacecraft crossed the heliopause, the boundary to interstellar space. On that day, the probe’s Plasma Science Experiment (PLS) instrument noted a sudden drop in the Sun’s plasma particles, coupled with an uptick in cosmic rays originating outside the solar system.
This does not mean that the Voyager probes have left the solar system—it could take 30,000 years for them to clear that border. But it does mean they are out of the heliosphere, which is a bubble-like expanse created by the Sun’s forces, especially the solar wind. The heliopause is the border between the heliosphere and interstellar space, where cosmic rays become more influential than the solar wind. Voyager 1 crossed it in 2012, and both probes are now over 11 billion miles from Earth.
“We're all happy and relieved that the Voyager probes have both operated long enough to make it past this milestone," Suzanne Dodd, Voyager project manager at NASA's Jet Propulsion Laboratory (JPL) said in a statement. "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."
NASA scientists are particularly excited to continue receiving plasma readings. Voyager 1’s PLS instrument broke down in 1980, making Voyager 2 the first probe to send back plasma data from the heliopause, and beyond. These observations are useful for understanding the interactions between the interstellar medium and the outer reaches of the heliosphere, a region that has only been directly explored by the Voyager probes.
The journey continues.
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