Most recently, a rapid drop in lower-energy particles (originating from the sun) coincided with a noticeable increase in high-energy particles (originating from interstellar space) leading many to speculate that Voyager 1 had officially left the solar system's heliopause. However, NASA scientists aren't yet ready to call Voyager 1 an "interstellar mission."
"If we were judging by the charged particle data alone, I would have thought we were outside the heliosphere," said Stamatios Krimigis, principal investigator of the low-energy charged particle instrument, based at the Johns Hopkins Applied Physics Laboratory, Laurel, Md. "But we need to look at what all the instruments are telling us and only time will tell whether our interpretations about this frontier are correct."
"We are in a magnetic region unlike any we've been in before - about 10 times more intense than before the termination shock - but the magnetic field data show no indication we're in interstellar space," said Leonard Burlaga, a scientist on the Voyager magnetometer team at NASA's Goddard Space Flight Center in Greenbelt, Md. "The magnetic field data turned out to be the key to pinpointing when we crossed the termination shock. And we expect these data will tell us when we first reach interstellar space."