The spacecraft is just the second ever to venture beyond the boundary that separates us from the rest of the galaxy.
IN THE BLACKNESS of space billions of miles from home, NASA’s Voyager 2 marked a milestone of exploration, becoming just the second spacecraft ever to enter interstellar space in November 2018. Now, a day before the anniversary of that celestial exit, scientists have revealed what Voyager 2 saw as it crossed the threshold—and it’s giving humans new insight into some of the big mysteries of our solar system.
The findings, spread across five studies published today in Nature Astronomy, mark the first time that a spacecraft has directly sampled the electrically charged hazes, or plasmas, that fill both interstellar space and the solar system’s farthest outskirts. It’s another first for the spacecraft, which was launched in 1977 and performed the first—and only—flybys of the ice giant planets Uranus and Neptune.
Voyager 2’s charge into interstellar space follows that of sibling Voyager 1, which accomplished the same feat in 2012. The two spacecrafts’ data have many features in common, such as the overall density of the particles they’ve encountered in interstellar space. But intriguingly, the twin craft also saw some key differences on their way out—raising new questions about our sun’s movement through the galaxy.
“This has really been a wonderful journey,” Voyager project scientist Ed Stone, a physicist at Caltech, said in a press briefing last week.
“It’s just really exciting that humankind is interstellar,” adds physicist Jamie Rankin, a postdoctoral researcher at Princeton University who wasn’t involved with the studies. “We have been interstellar travelers since Voyager 1 crossed, but now, Voyager 2’s cross is even more exciting, because we can now compare two very different locations … in the interstellar medium.”
Inside the bubble
To make sense of Voyager 2’s latest findings, it helps to know that the sun isn’t a quietly burning ball of light. Our star is a raging nuclear furnace hurtling through the galaxy at about 450,000 miles an hour as it orbits the galactic center.
The sun is also rent through with twisted, braided magnetic fields and, as a result, its surface constantly throws off a breeze of electrically charged particles called the solar wind. This gust rushes out in all directions, carrying the sun’s magnetic field with it. Eventually, the solar wind smashes into the interstellar medium, the debris from ancient stellar explosions that lurks in the spaces between stars.
Like oil and water, the solar wind and the interstellar medium don’t perfectly mix, so the solar wind forms a bubble within the interstellar medium called the heliosphere. Based on Voyager data, this bubble extends about 11 billion miles from the sun at its leading edge, surrounding the sun, all eight planets, and much of the outer objects orbiting our star. Good thing, too: The protective heliosphere shields everything inside it, including our fragile DNA, from most of the galaxy’s highest-energy radiation. [ … ]