A space probe launched 35 years ago has become the first man-made object to leave the solar system, scientists said yesterday.

Voyager 1 is on a lonely journey away from the sun and its planets, but still communicating with Earth.

According to a report, the probe has travelled beyond the heliosphere, the region of space dominated by the sun.

At a distance of more than 17 billion kilometres from the sun, it was said to have left the solar system and entered a twilight zone on the frontier of interstellar space.

But American space agency Nasa has disputed the claim and called it premature. It denies that the probe is now outside the solar system.

A paper for the journal Geophysical Research Letters points to evidence in the form of a dramatic change in the radiation surrounding the craft.

‘Anomalous’ cosmic rays trapped in the outer heliosphere have all but vanished, dropping to less than one per cent of their previous level. At the same time, the intensity of galactic cosmic rays originating from outside the solar system appears to have doubled.

Lead author US astronomer Bill Webber, from New Mexico State University in Las Cruces, said: “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 exited the heliosphere.

“It’s outside the normal heliosphere, I would say that. We’re in a new region. And everything we’re measuring is different and exciting.”

Voyager 1 and sister probe Voyager 2 were launched in 1977 to explore the outer planets.

Both are now on an extended trip to the stars. Each craft carries a gold-plated audiovisual disc for the benefit of any intelligent aliens that might pick them up.

The discs carry photos of the Earth and its life forms, a range of scientific information, spoken greetings, earthly sounds such as a baby crying, and music including works by Mozart and gospel blues singer Blind Willie Johnson. In 15 years’ time, Voyager 1’s plutonium power source will run out, cutting off all communication as the probe coasts on through the vast emptiness of space.

Edward Stone, Voyager project scientist at the California Institute of Technology in Pasadena, said: “The Voyager team is aware of reports today that Nasa’s Voyager 1 has left 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.”