Voyager 1 interstellar space

On this day in 2012, NASA’s Voyager 1 spacecraft entered interstellar space, becoming the first human-made object to slip into the gap between stars. Scientists didn’t know right away that the milestone had occurred—there are no road signs welcoming visitors to interstellar space—but gradually gathered data from the decades-old probe over the next year to make the case. The primary evidence came from a precipitous drop in the concentration of sluggish particles from the sun combined with an increase in more energetic particles, presumably ejected by other stars. Those measurements and others convinced Voyager scientists that the probe had left the solar system’s heliosphere, which is a sort of magnetic balloon inflated by charged particles from the Sun. The announcement came in September 2013. Although Voyager has entered interstellar space, it has not actually left the solar system—the Sun’s gravity still dominates, and there are plenty of comets and other Sun-orbiting objects that reside much farther away than Voyager 1’s current position. But now that Voyager has escaped the heliosphere, it can determine what the environment is like outside of our solar system’s protective bubble.Voyager 2 may join its sibling probe in interstellar space within the next couple of years.

Date in History: 25 August 2012