Over 40 years after it left planet Earth, the Voyager 2 space probe has crossed over into interstellar space, NASA announced on Monday.
The US space agency said that the spacecraft has exited the outer boundary of the heliosphere — the bubble of solar wind that the sun creates around itself — in early November.
Voyager 2 is now some 11 billion miles (about 18 billion kilometers) from Earth and is the second human-made object to pass into the vast area of interstellar space.
NASA was able to determine Voyager 2's position based on data gathered from one of its key instruments — a Plasma Science Experiment (PLS). The instrument recorded a steep drop in the speed of solar wind particles on November 5 and hasn't recorded any solar wind flow since.
Its twin probe, Voyager 1, was the first to cross into interstellar space in 2012, although its PLS instrument stopped working decades ago.
'Unprecedented glimpse' into interstellar space
Nicola Fox, director of the Heliophysics Division at NASA Headquarters, said in a statement that the Voyager probes have a "special place" in her department.
"Our studies start at the sun and extend out to everything the solar wind touches. To have the Voyagers sending back information about the edge of the sun's influence gives us an unprecedented glimpse of truly uncharted territory," she added.
Both the Voyager 1 and Voyager 2 launched from the US in 1977 and have carried out flyby missions on Jupiter, Saturn, Uranus and Neptune — extending long past their five-year lifespans.
Mission operators are still able to communicate with Voyager 2, although it currently takes 16.5 hours for information to travel from the probe back to Earth since the data is moving at the speed of light.
"By comparison, light traveling from the Sun takes about eight minutes to reach Earth," NASA said in its statement.
Not leaving solar system soon
NASA estimates that the probes could last another five to 10 years, but the extreme cold outside the vehicles and their waning power supply means they will eventually become less useful, said Voyager project manager Suzanne Dodd.
"I think we're all happy and relieved that the Voyager probes have both operated long enough to make it past this milestone," Dodd said.
Both of the spacecraft are still technically in our solar system, as they have yet to pass beyond it's outer edge known as the Oort Cloud.
It could be another 30,000 years before they would fly beyond it and come close to other stars, NASA said.
In the meantime, the probes are still sending crucial information back to Earth about the area beyond the heliosphere — and the space between the stars.
rs/jm (AP, dpa)