NASA's Voyager 1, launched in 1977, appears to be on the verge of becoming the first spacecraft to leave the solar system and begin a new journey in outer space, experts say.

Scientists are intrigued by the recent increase in cosmic rays hitting the spacecraft, which for decades has snapped images of the Earth and other planets in the solar system as it makes its long journey into outer space.

"The latest data from Voyager 1 indicate that we are clearly in a new region where things are changing quickly," said a statement from Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena.

"This is very exciting. We are approaching the solar system's final frontier."

These cosmic rays, which are high energy particles that are accelerated to near-light speed by distant supernovas and black holes, have been bombarding the spacecraft with greater frequency, NASA said.

The galactic cosmic rays encountered by Voyager 1 increased about 25 percent from January 2009 to January 2012.

"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," he said.

Those signals could mean that Voyager is "on the verge of a breakthrough 18 billion kilometers from Earth," NASA said.

Researchers had previously said they expected Voyager 1 would leave the solar system and enter interstellar space -- between the end of the Sun's influence and the next star system -- at some point in the next two years.

NASA has described Voyager 1 and its companion Voyager 2 -- now more than 9.1 billion miles (14.7 billion kilometers) away from the Sun -- as "the two most distant active representatives of humanity and its desire to explore."