Forty-one years after it launched into space, NASA’s Voyager 2 spacecraft has crossed the outer edge of the heliosphere. Called the heliopause, this boundary is where the tenuous, hot solar wind meets the cold, dense interstellar medium. Voyager 2’s twin probe, Voyager 1, crossed this boundary in 2012, but Voyager 2 carries a working instrument that will provide first-of-its-kind observations of the nature of this gateway into interstellar space. This...
