http://blog.chron.com/sciguy/2012/10/more-evidence-that-voyager-has-exited-the-solar-system/
"To cross this boundary scientists say they would need to observe three things: 1. An increase in high-energy cosmic rays originating from outside our solar system 2. A drop in charged particles emanating from the sun. 3. A change in the direction of the magnetic field."
