NASA launched the Voyager 1 probe back in 1977 and sent it on its journey through our solar system to study planets as it passed on its way outside of our solar system. Back in December of 2011 NASA mentioned that Voyager 1 was entering into a new region of space, the stagnation region, which is sort of like a bubble around our solar system. This region is one of the last indicators that the probe is still within our solar system.
Voyager 1 may soon become the first manmade object to leave the solar system, and the probe could leave our solar system much sooner than previously thought. Voyager 1 and Voyager 2 are currently still in what's known as the Heliosheath where the sun's solar wind is slowed by the pressure of interstellar gas. Both of the probes are still transmitting the data about the location through the Deep Space Network. The fact that a pair probes constructed in the 70s are still functional is impressive.
The scientists are watching three data sets to determine when the probe leaves our solar system. One of those data sets is the amount of galactic cosmic rays Voyager is encountering. The second data set is the intensity of energetic particles created inside the heliosphere. Scientists say that when the intensity subsides significantly, they will know Voyager has left our solar system. While Voyager is still within our solar system's heliosphere, magnetic field lines are running east to west and scientists believe when the probe passes into interstellar space, magnetic field lines are expected to be in a more north-south direction.
“From January 2009 to January 2012, there had been a gradual increase of about 25 percent in the amount of galactic cosmic rays Voyager was encountering,” said Mr. Stone. “More recently, we have seen very rapid escalation in that part of the energy spectrum. Beginning on May 7, the cosmic ray hits have increased five percent in a week and nine percent in a month.”