Launched in 1977, Voyager 1 and Voyager 2 took different routes through the outer solar system, each touring the gas giant planets before bending toward separate spots along the heliopause, the boundary zone between the sun’s constant stream of plasma and the diffuse debris field that is the interstellar medium. Voyager 1 crossed first, becoming humankind’s first interstellar object in 2012. Now, as our Michael Greshko reports, NASA has confirmed that Voyager 2 finally punched through last year, and it is seeing some unexpected conditions out there on the solar fringes.

For me, the Voyager mission is as emotional as any Oscar-worthy drama. Both craft carry copies of the iconic Golden Record, a literal labor of love that