LAS CRUCES, N.M., March 20 (UPI) -- The U.S. Voyager-1 spacecraft launched in 1977 may have left the solar system, some scientists say, and if so would be the first man-made artifact to exit.
After traveling for 35 years, the space probe appears to have traveled beyond the influence of the Sun and exited the heliosphere, the region of space dominated by the Sun and its wind of energetic particles, a study to be published in the journal Geophysical Research Letters indicates.
The edge of the heliosphere is considered the boundary between our solar system and the surrounding interstellar medium of gas and dust that pervades the Milky Way galaxy.
Researchers say Voyager has been detecting a decrease in a type of cosmic rays that remain trapped in the outer heliosphere, while a different type of "galactic" cosmic rays -- radiation from outside the solar system -- have dramatically increased.
"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," astronomer Bill Webber, at New Mexico State University in Las Cruces, said, calling the transition boundary the "heliocliff."
Voyage, still traveling after its initial goal of studying the outer planets Jupiter, Saturn, Uranus and Neptune, is now more than 11 billion miles from Earth.