Nasa’s Voyager 2 has become the second human-made object to fly away from the sun into the space between the stars.
Voyager 2 last month exited “this bubble that the sun creates around itself”, Nasa mission scientist Ed Stone said.
The spacecraft is beyond the outer boundary of the heliosphere, 11 billion miles from Earth.
It is trailing twin Voyager 1, which reached interstellar space in 2012 and is 13 billion miles from Earth. Interstellar space is the vast emptiness between star systems.
Even though they are out of the sun’s bubble, the Voyagers are still technically in our solar system, Nasa said.
Scientists maintain the solar system stretches to the outer edge of the so-called Oort Cloud. It will take about 30,000 years for the spacecraft to get that far.
Scientists know that Voyager 2 has left the sun’s influence because of four different instruments measuring solar particles and different types of rays.
They showed a dramatic change on November 5, indicating the spacecraft was between the stars.
One of the instruments measures solar plasma and this is the first time Nasa has seen a drop in that key instrument. The same instrument was not working on Voyager 1.
The twin Voyagers launched from Cape Canaveral, Florida, in 1977, and zipped by Jupiter, Saturn, Uranus and Neptune.
Voyager 2 has already logged more than 18.5 billion miles on its interstellar trip going 34,191mph.
“Both spacecrafts are very healthy if you consider them senior citizens,” Voyager project manager Suzanne Dodd said.
She said the probes should last at least five, maybe 10 more years, but the cold — the temperature outside the vehicles is about minus 45C — and waning power supply will eventually end their usefulness.
They will keep travelling and in 40,000 years or so they will get close to the next stars, or the stars, which are moving faster, will get close to them, Mr Stone said.