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According to Popular Science (This article and its images were originally posted on Popular Science October 9, 2018 at 11:33AM.)
Space is vast, but it’s not entirely empty. Take a closer look, and you’ll find that even the gulfs between stars are threaded with speeding particles, survivors of ancient, cataclysmic events that launched them across the universe at nearly the speed of light.
The Voyager 2 spacecraft, which left Earth more than 40 years ago to survey the outer planets, just detected a 5 percent uptick in these cosmic refugees, NASA announced. The new measurements bring a long-expected sign that the probe is approaching the edge of the sun’s protective influence, which for many researchers defines the line between interplanetary and interstellar space. Crossing that boundary will provide a valuable second data point in the quest to determine its shape, but precisely when the probe will leave the solar system remains unknown.
“We’re seeing a change in the environment around Voyager 2, there’s no doubt about that,” said Voyager Project Scientist Ed Stone of Caltech in a press release. “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.”
If you feel like you’ve heard this story before, it’s because you have. The craft’s speedier sibling, Voyager 1, returned data showing a similar increase of interstellar cosmic rays in May of 2012. In addition to light, the sun also spits out a plasma of charged particles in all directions. Too hot to contain, this solar wind streams outward past the planets, pushing back on of the interstellar particles and creating a bubble researchers call the heliosphere. Three months later, on August 25th, Voyager’s aging instruments detected a drop in solar particles and a further rise in interstellar particles—strong evidence that it had left the heliosphere at last.
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