Voyager 1, sent out into the great unknown some 35 years ago, has been on the verge of leaving the solar system for a few years. Now the indicators are finally beginning to mark the probe's location as beyond the influence of the sun.
It was 35 years ago that NASA sent Voyager 1 on its way, with the mission of becoming the first man-made craft to leave to solar system and enter interstellar space; to travel to the farthest reaches of the galaxy, never to return again. Along with equipment to measure the surroundings of the probe is a golden disc, etched with images of humans and a visual depiction of the solar system, as well as instructions for how to access the sounds, music and greetings from earth recorded upon it; an outstretched hand to any other beings out there who may one day find it. Now, the first step on Voyager's journey is just about completed: It's about to leave the Solar System.
This is something which has been close to happening for years, but has been very difficult to precisely determine. We don't know particularly much about the border between our solar system and interstellar space, and the line between the two is rather fuzzy. Still, two indicators which NASA has been considering as signs for crossing the border were just detected by Voyager; the signs being related to the movement of charged particles around the probe. Somewhat prematurely, the American Geophysical Union released a statement this morning saying that the probe had indeed left the solar system, but this isn't quite true yet – it's only very close.
The final indicator of interstellar space is a change in magnetic field lines (arrows in the image). Image credit: NASA/JPL-Caltech
Apart from the two discovered indicators mentioned above, NASA and JPL are waiting for one more indicator; a change in the direction of magnetic field lines, before it officially announces the probe as outside the Sol system. The Voyager team issued this statement:
"It is the consensus of the Voyager science team that Voyager 1 has not yet left the solar system or reached interstellar space. In December 2012, the Voyager science team reported that Voyager 1 is within a new region called 'the magnetic highway' where energetic particles changed dramatically. A change in the direction of the magnetic field is the last critical indicator of reaching interstellar space and that change of direction has not yet been observed."
That being said, the probe is now outside the region effected by the sun's heliosphere; as the AGU report states: “It appears that Voyager 1 has exited the main solar modulation region, revealing Hydrogen and Helium spectra characteristic of those to be expected in the local interstellar medium.” So whether or not we've officially left the solar system, we're definitely someplace new, and different… and the final crossing will likely happen soon.