A new paper published today in Geophysical Review Letters confirms that the intensities of anomalous cosmic rays and galactic cosmic rays “changed suddenly and decisively on August 25th” when the Voyager 1 was 121.7 astronomical units from the Sun. That suggests the craft has left the heliosphere and is officially outside of the Solar System.
Preliminary results were released last year, but this paper, linked to above, is a peer-reviwed confirmation of those findings. Plus, it has been released into the public domain, so you can dig in to all the nitty-gritty science you want.
Update: Not everyone agrees. The Voyager team at NASA’s Jet Propulsion Laboratory says there’s still a ways to go before the craft reaches interstellar space. There’s bound to be more healthy debate. That’s science for you.