Row between scientists over position of Nasa's Voyager 1 spacecraft continues

Two members of the Voyager team believe that the space-probe is still within the influence of the Sun, in a region known as the heliosphere

This artist's rendering provided by NASA shows the Voyager spacecraft35 years after leaving Earth (AP)

Scientists have questioned the announcement by Nasa last year that the Voyager 1 spacecraft, which was launched in 1977 to study Jupiter and Saturn, has finally left the Solar System for interstellar space.

Two members of the Voyager team believe that the space-probe – the furthest man-made object from Earth – is still within the influence of the Sun, in a region known as the heliosphere, which means it has not yet left the Solar System.

George Gloeker and Len Fisk of the University of Michigan have devised a test that Voyager 1 must pass if the claim is to be recognised. They expect the space-probe will eventually pass into interstellar space, but that it has not done so yet.

“The proof is in the pudding,” said Professor Gloeker, who has been working on the Voyager mission since 1972 and has been a vocal opponent of Nasa’s claim that the spacecraft has finally entered interstellar space.

The two scientists predict that sometime in 2015 Voyager 1 will encounter a reversal in the magnetic polarity of the solar wind, and this will be picked up by its on-board instruments, proving that the spacecraft is indeed still within the heliosphere.

“If that happens, I think if anyone still believes Voyager 1 is in the interstellar medium, they will really have something to explain. It’s a signature that can’t be missed,” Professor Gloecker said.

Nasa said last year that it has been deliberately cautious about saying whether Voyager 1 has left the Solar System following a series of claims from various scientists that it has. However, the space agency was finally convinced by Voyager’s detection of interstellar plasma in April 2013.

The argument over whether Voyager 1 has left the Solar System has raged for several years and is a prime example of how difficult it is for scientists to reach honest agreements over difficult problems – in this case complicated by a distance of more than 9.5 billion miles.