Voyager 2′s Journey Beyond The Solar System Reveals New Cosmic Secrets

The Voyager 2 spacecraft spent more than four decades surfing the solar wind away from the sun and out into the galaxy. Then, in less than a day, the probe burst from our sun’s protective bubble out into an interstellar sea of alien particles.
The exact shape of that bubble—which repels about 70 percent of harmful cosmic radiation—and how the inside mixes (or doesn’t mix) with the outside, are questions that have troubled researchers for decades. They’ve caught indirect glimpses of this edge of our cosmic backyard with radio waves and other observations, but their first direct contact with the mysterious boundary came when Voyager 1 sailed through it in 2012. Now Voyager 2, which joined its predecessor on the outside, last November, has provided a second taste, in a second location. After a year of analysis, researchers have published a series of papers in the journal Science detailing Voyager 2’s direct measurements of the solar bubble that surrounds us—concrete knowledge of a physical structure that was purely theoretical while the mission was being planned.
“We didn’t know 50 years ago whether there’d even been a boundary there,” says Donald Gurnett, a professor emeritus at the University of Ohio and principal investigator of the Voyager plasma wave instruments.
While the primary Voyager missions were all about planetary exploration, the extended missions focused on the solar system as a whole. In addition to lighting up the sky, the sun also blasts out a solar wind of charged particles in all directions at around a million miles an hour. Although we tend to think of “outer space” as empty, this wind actually fills the solar system with thin plasma (a kind of hot, energized gas) that gets thinner as the wind blows further from the sun. “It’s like spraying perfume into a room,” Gurnett says.
Eventually the solar plasma gets so thin—around one electron per Rubik’s Cube of space—that it can’t push away the stuff of interstellar space any longer. There’s plasma out there too, and it’s about 20 times thicker outside than it is inside the range of the sun’s influence—a zone known as the heliosphere. This sharp change from thin plasma to thick plasma was one indication that the crafts had entered interstellar space. “What we are measuring is our backyard,” says Merav Opher, a plasma physicist at Boston University who was not directly involved with the Voyager teams. “We’ve never been outside of our home in the galaxy.”
But now that the Voyagers are getting out into the local neighborhood (other defunct spacecraft are too, but they aren’t still taking data), researchers are comparing measurements from their respective locations and piecing together anything they can about the heliosphere’s overall shape and behavior. Voyager 1, for instance, managed to indirectly catch some whiffs of interstellar plasma while still in the heliosphere—indicating that the sun erects a drafty barrier around the solar system. “It’s almost like somebody opened a window and we got some interstellar material ahead of the boundary
During last year’s departure, however, Voyager 2 didn’t feel any such interstellar gusts. It also experienced solar breezes all the way up to the edge—a zone where Voyager 1 had reported doldrums.

By – Abhishek Singh
Content - https://www.popsci.com/story/space/voyager-2-enters-interstellar-space/