Out of this world: 35 years after mission to boldly go where no spacecraft has gone before - Voyager 1 'exits' Solar System

Probe has reached the edge of interstellar space, where no manmade object has gone before

It is the furthest man-made object in space. It has travelled more than 11 billion miles since it was launched nearly 36 years ago. And now Voyager 1 has boldly gone where no spacecraft has gone before – it has left the outer reaches of the Solar System.

It is the furthest man-made object in space. It has travelled more than 11 billion miles since it was launched nearly 36 years ago. And now Voyager 1 has boldly gone where no spacecraft has gone before – it has left the outer reaches of the Solar System.

After several years of debate over whether the Voyager 1 probe, launched in September 1977, has crossed the cosmic-equivalent of the doldrums separating the Solar System from interstellar space, scientists believe the spacecraft has finally travelled beyond the influence of the Sun.

Voyager 1, the second of a pair of twin space probes, was launched in the same year that Elvis died, Donna Summer reached number 1 with “I Feel Love” and the Sex Pistols began to shock the suburbs.

It was originally designed to explore nearby planets but after a string of important discoveries, including the observations of active volcanoes on Jupiter’s moon Io and the rings of Saturn, the Voyager 1 mission was extended. Meanwhile, Voyager 2 went on to the more distant planets of Uranus and Neptune.

Scientists believe that Voyager 1, which was launched after Voyager 2 but has now overtaken it in terms of its distance from the Earth, has left a region of space known as the heliosphere, which is dominated by the stream of energetic particles emanating from the Sun called the solar wind.

Measurements taken on 25 August last year, but published online now in the journal Geophysical Research Letters, reveal that Voyager 1 underwent dramatic changes in its exposure to radiation levels. Scientists said that their measurements changed “suddenly and decisively”.

The anomalous cosmic rays trapped in the outer heliosphere of the Solar System all but vanished – dropping to less than 1 per cent of previous amounts – while galactic cosmic rays from deep space spiked to twice the highest intensities previously seen. Bill Webber, professor of astronomy at New Mexico State University in Las Cruces, said the data suggests that Voyager 1 has entered a new region of space that no probe has visited before – a signal that it has finally left the Solar System and is about to enter interstellar space.

“Within just a few days, the heliospheric intensity of trapped radiation decreased, and the cosmic ray intensity went up as you would expect if it had exited the heliosphere,” Professor Webber said. “It’s outside the normal heliosphere. We’re in a new region. Everything we’re measuring is different and exciting,” he said.

The latest results suggest that Voyager 1 has jumped off the “heliocliff”, Professor Webber added, and entered a region where the solar wind blows no more and can no longer protect the space probe from the intense cosmic radiation of deep space.

However, Ed Stone, Voyager project scientist at Caltech in California, said that the probe is still probably within the Solar System. “It is the consensus of the Voyager science team that Voyager 1 has not yet left the Solar System or reached interstellar space…. A change in the direction of the magnetic field is the last critical indicator of reaching interstellar space and that change of direction has not yet been observed.”

Voyager 1 carries a gold-plated copper disc carrying images and sounds from Earth, including greetings in 55 languages and a humpback whale song.