Distant probe phones home

An artist's impression of Pioneer 10 in space

By BBC News Online technology correspondent Mark Ward

After almost eight months of silence, the American space agency, Nasa, has re-established contact with the Pioneer 10 spacecraft.

Our main mission was just to go to Jupiter and we did that in the period of 21 months and here it is almost not only 21 years but 29 years later

Dr Larry Lasher

Agency scientists had feared that the 29-year-old craft had stopped working, but this weekend the Nasa said it had received a faint signal from the probe.

The faithful craft is still sending back useful data even though it is over 11 billion kilometres (seven billion miles) from Earth.

In the early days of its mission, it was the first to take close-up images of the planet Jupiter.

Distant message

On 19 August, 2000, Nasa lost contact with the Pioneer 10 space probe, leading scientists to speculate that the craft had gone silent.

But this weekend a satellite dish in Madrid received a signal from the craft. "Pioneer 10 lives on," said Pioneer project manager Larry Lasher.

Dr Lasher said his team had tried to test whether the space probe was still functioning by sending it a strong signal. Almost 22 hours later, they received a response.

"Our main mission was just to go to Jupiter and we did that in the period of 21 months and here it is almost not only 21 years but 29 years later," Dr Lasher told the BBC.

But it is likely to become increasingly difficult to contact Pioneer 10 because it only sends back data when first contacted by Nasa.

Alien life

Pioneer's official mission finished in March 1997, but Nasa regularly kept in touch with the craft because it was still working and was sending back data used to do work on chaos theory.

Pioneer 10 was launched on 2 March, 1972. It was the first spacecraft to pass through the asteroid belt and take some of the first close-up images of Jupiter.

In 1983, it became the first man-made object to leave the Solar System when it passed through Pluto's orbit. Until 17 February, 1998, it was the most remote man-made object, and was over 11 billion kilometres (seven billion miles) from Earth. On that date its distance was exceeded by Voyager One which is now 12,019,000,000 kilometres away.

The next important encounter in Pioneer's life is due in two million years when it passes one of the stars in the constellation Taurus.

The craft is carrying a plaque made of gold that shows Earth's location in the Solar System and a message of greeting for any alien life it should happen to encounter.