The Voyager 2 spacecraft was launched 41 years ago, and is now 11 billion miles from Earth. While that itself is amazing, it is even more staggering that the spacecraft is still sending back data, decades after the communication system was expected to fail. Voyager 2 measures cosmic rays. A recent increase in the number of cosmic rays detected indicate that the spacecraft is reaching the edge of the heliosphere, the limit of our sun's solar wind.
It’s believed that the heliosphere blocks a lot of these rays from reaching our solar system, but as you travel closer to the edge and the barrier starts to thin out, more cosmic rays become detectable. Voyager 2’s increased measurements suggest that it’s inching closer to the heliopause, and could soon enter the interstellar medium.
And if we’re going off of history, the craft could be crossing the threshold any day now. In 2012, Voyager 1 experienced a similar spike in cosmic rays about three months before it passed through the heliopause, becoming the first craft to invade interstellar space.
The exact location of Voyager 2 is a guess based on the data it sends. Read more about the milestone at Discover magazine. -via reddit
You can keep up with the status of both Voyager 1 and Voyager 2 at NASA.
(Image credit: NASA/JPL-Caltech)