Voyager 1 truly has gone where no man (or spacecraft) has gone before. Huge changes in the environment around the space probe indicate that it has gone beyond the heliosphere, our little corner of space that's dominated by the influence of the sun.
It only took 35 years for the craft to travel more than 11 billion miles from the sun and possibly exit the solar system. What scientists are seeing is a huge spike in galactic cosmic rays.
"Within just a few days, the heliospheric intensity of trapped radiation decreased, and the cosmic ray intensity went up as you would expect if it exited the heliosphere," said Bill Webber, professor emeritus of astronomy at New Mexico State University in Las Cruces.
The change in rays was observed on August 25 last year, but the findings have just been detailed in a paper for Geophysical Research Letters, a publication of the American Geophysical Union.
Though Webber said he feels pretty confident that Voyager 1 has gone off the "heliocliff," there is still some debate among scientists about what kind of zone the spacecraft has entered. "It's outside the normal heliosphere; I would say that. We're in a new region. And everything we're measuring is different and exciting," he said.
This small step for a spacecraft could have big implications for our understanding of space outside our heliosphere. In the meantime, scientists will continue to sort out whether or not Voyager 1 has reached interstellar space. The paper concludes with, "Future observations at V1 will hopefully settle many of these issues as the spacecraft proceeds further into this uncharted region."
Update, 11:20 a.m. PT: NASA says it doesn't believe Voyager 1 has quite left the solar system. In a statement, Edward Stone, Voyager project scientist based at the California Institute of Technology, Pasadena, Calif., says, "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."