NASA’s Voyager spacecraft may be billions of miles away and over 40 years old, but they’re still making significant discoveries, as new research reveals.
A paper published today in the Astronomical Journal describes an entirely new form of electron burst, a discovery made possible by the intrepid Voyager probes. These bursts are happening in the interstellar medium, a region of space in which the density of matter is achingly thin. As the new paper points out, something funky is happening to cosmic ray electrons that are making their way through this remote area: They’re being reflected and boosted to extreme speeds by advancing shock waves produced by the Sun.
By itself, this process, in which shock waves push particles, is nothing new. What is new, however, is that these bursts of electrons are appearing far ahead of the advancing shock wave, and that it’s happening in a supposedly quiet region of space. The new paper was co-authored by astrophysicist Don Gurnett from Iowa University.
Launched in 1977, Voyager 1 and Voyager 2 have done tremendous work for king and country, and they’re still enabling meaningful scientific work after so many years. But instead of studying active volcanoes on Jupiter’s moon Io or taking glorious photos of Saturn’s rings, these probes are now studying the uncharted waters beyond the heliopause—the zone between the hot solar plasma and the cooler interstellar medium at the outer reaches of the solar system.
“This is analogous to seeing light reflected from the cloud of a far-away explosion, and then hearing the boom at a later time.”
Voyager 1 is currently 14.1 billion miles away, and Voyager 2 is 11.7 billion miles away (the probes were launched within 16 days of one another, but they were sent on different trajectories during their respective sojourns through the solar system). Voyager 1 crossed the heliopause boundary in 2012, and Voyager 2 did the same in 2018. They’re currently traveling through a region referred to as the very local interstellar medium (VLISM), according to the study. The Voyager probes are the most distant human-made objects ever.
Some may quibble about the term “interstellar medium” and claim that the Voyager probes are still technically inside the solar system, but Gurnett is adamant that the Voyager probes are indeed traveling through interstellar space, which literally means the “medium between the stars,” as he explained by phone. “We won that argument,” said Gurnett, “but of course I’m biased.” The pressure of gas at the location of the Voyager probes, he said, is equal to the pressure of gas we would expect to see in interstellar space. To him, that means the probes are inside the interstellar medium.
In 2012, Gurnett at his colleagues declared that Voyager 1 crossed into interstellar space, a claim confirmed by NASA the following year.
Years ago, before the NASA probes entered this region of space, “we thought