Launched on September 5, 1977 from Space Launch Complex 41 at the Cape Canaveral Air Force Station, Florida, United States, Voyager 1 is now about 18 billion kilometers (5 billion miles) away from the Earth, what scientists measure as 120 astronomical units, where one AU is equal to the average distance between the Sun and the Earth.
Stone, who is with the California Institute of Technology (Pasadena), adds, "This is very exciting. We are approaching the solar system's final frontier."
He also states, "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."
Further, "A sharp increase in cosmic rays could herald Voyager 1's long-awaited breakthrough to interstellar space. More recently, however, we have seen a very rapid escalation in that part of the energy spectrum. Beginning on May 7, 2012, the cosmic ray hits have increased five percent in a week and nine percent in a month."
For more on this exciting story of humankind's first probe to leave the solar system and to venture out there into interstellar space, please read the NASA article "Voyager 1 at the Final Frontier".
The YouTube video "ScienceCasts: Voyager 1 at the Final Frontier" appears below.