Voyager 1 Has Entered Interstellar Space

After 36 years, we can wave goodbye to our pal.

Voyager 1

One of the two identical Voyager probes, as photographed by NASA.NASA

36 years after launch, Voyager 1 has officially left the solar system, according to NASA officials.

We've been waiting for years for Voyager to break through the last boundary of the heliosphere, which is the region of space which particles spurted out by our sun can reach (roughly corresponding to our understanding of our own solar system). Voyager is the very first manmade object to break its way through the heliosphere, on its way out to a distant star. NASA estimates that it'll get near to its destination star in about 40,000 years. (Yeah, space is pretty big.)

The border of the heliosphere isn't visible; it's not like breaking through the tape at the end of a marathon and knowing you're finished and on the other side. NASA measures the density of plasma from the sun, with the understanding that there's higher density right at the border of the heliosphere (called the heliopause) compared to the space outside the heliosphere. Some complex work, published in the current issue of Science, indicates that this transition happened on August 25th of last year.

_Update:** So, a little more on what's happening here: the border of the "solar system" is sort of unclear. "Solar system" is commonly used to mean our immediate planetary neighbors, but scientists use the term to refer to everywhere in space at which our sun's pull is greater than that of any other star. By that definition, Voyager hasn't left the solar system; it's passed through the heliopause, but it'll take another 300 years before it reaches the Oort Cloud, the spot most scientists agree is the border between our solar system and the next. In the Oort cloud, the gravitational pull of other stars is greater than that of our own--and Voyager isn't there quite yet.

Read more about Voyager's milestone here.