NASA's Voyager probe has left the solar system simply because there was nowhere else for it to go.
BBC News reported the spacecraft, launched in 1977, is the first manmade object to leave the solar system. When it was originally launch, NASA commissioned it to explore the outer planets, but now it has shown no signs of wanting to stop.
The Voyager is approximately 12 million miles from Earth and is so far away, it takes ground control 17 hours to receive a radio signal sent from its location.
"This is really a key milestone that we'd been hoping we would reach when we started this project over 40 years ago - that we would get a spacecraft into interstellar space," chief mission scientists Ed Stone told BBC. "Scientifically it's a major milestone, but also historically - this is one of those journeys of exploration like circumnavigating the globe for the first time or having a footprint on the Moon for the first time. This is the first time we've begun to explore the space between the stars."
Voyager's sensors had been indicating previously that its surroundings had changed, but it was not until scientists collected data from the Plasma Wave Science (PWS) instrument that they confirmed the jump to interstellar space. The PWS is capable of detecting the density of charged particles in the craft's vicinity.
"Voyager-1 will be in orbit around the center of our galaxy with all its stars for billions of years," said Stone.
Based on data from earlier this year and later in 2012, the team discovered a 100-fold leap in the number of protons per cubic meter of space. Previously, the scientists had theorized such a jump would mean the Voyager would have left the sun's magnetic field.
After further analysis, NASA confirmed Voyager likely left the solar system some time around Aug. 25, 2012.
"The idea that the spacecraft would then exit the Solar System altogether was so way out, figuratively as well as literally, that we didn't even discuss it then, although I suppose we knew it would happen someday," British planetary scientist Fred Taylor said. "Forty-three years later, that day has arrived, and Voyager is still finding new frontiers."
