'Boldly going where no probe has gone before': Nasa confirms Voyager 1 has left the solar system

It launched in the year Elvis died, just as the personal computer was making its public debut. And tonight, after months of feverish expectation, Nasa confirmed its Voyager 1 probe had entered the deep and unknown space between the stars and exited the solar system.

The probe officially becoming the first man-made object to leave the solar system was the culmination of a 36-year dream for Nasa who said it was a scientific and historic “milestone” that would allow humans to understand what exists in interstellar space for the first time.

Voyager 1 is thought to have exited the solar system on 25 August last year. Scientists noticed the probe underwent dramatic changes in its exposure to radiation levels - thought to be caused by cosmic rays trapped in the outer helio-heliosphere.

NASA said sensors on Voyager had long been indicating that its environment had changed, and data from the probe's Plasma Wave Science instruments - which measure the density of charged particles in the vicinity - had confirmed a predicted spike in particles.

“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,” said Professor Ed Stone, the original Nasa project scientist on Voyager at the Jet Propulsion Laboratory.

Described as the “little spacecraft that could”, Voyager was originally intended for a near-earth mission to study Jupiter and Saturn. But after it completed that stage in 1989, together with the Voyager 2 probe, the pair were steered towards deep space.

Voyager 2 trails behind and may take another three years before joining its twin on the other side of the solar divide.

“Voyager has boldly gone where no probe has gone before marking one of the most significant technological achievements in the annals of the history of science,” said John Grunsfeld, Nasa's associate administrator for the Science Mission Directorate.

It will now study exotic particles and other phenomena in a never-before-explored part of the universe and radio the data back to Earth. But being almost 12billion miles from earth means radio signals take 17 hours to reach NASA receivers.

Voyager 1 carries a gold-plated disc containing multicultural greetings, songs and photos, in case it bumps into an intelligent species.

“It took us 10 seconds to realize we were in interstellar space,” said Don Gurnett, a Voyager scientist at the University of Iowa who led the latest research, published in the journal Science.

But the Harvard astrophysicist Jonathan McDowell was sceptical. “I'm actually not going to believe it for another year or two until it's been solidly outside for a while,” he said.

Eventually, the Voyagers will run out of nuclear fuel and will have to power down their instruments, perhaps by 2025.