Nasa switches off "Voyager" instruments to save power

"If we didn't turn off an instrument on each Voyager probe now, they would probably only have a few months of power left before we would have to announce the end of the mission," explained project manager Suzanne Dodd.

The "Voyager" twins are the most distant man-made objects from Earth. The two unmanned probes were launched in 1977. They were intended to explore planets in the outer solar system, but ended up flying beyond the boundaries of the solar system. Swiss researchers are also involved in analyzing data from the probes.

Three out of ten instruments are still running

NASA also announced that an experiment on "Voyager 1", which consists of three telescopes that measure cosmic rays, was completed at the end of February. At the end of March, an instrument on "Voyager 2" that measures charged particles with low energy is to be switched off. Three of the original ten instruments will then still be running on each probe.

The twin probes use an energy system that generates electricity from the heat of radioactively decaying plutonium. According to Nasa, both lose around four watts every year. "Energy is running out," explained Dodd. Nevertheless, Nasa is trying to operate the two for as long as possible. In about a year, more instruments will probably have to be switched off. The probes could then possibly be operated until the 2030s.

Billions of kilometers away

Voyager scientist Patrick Koehn added: "The Voyager space probes have far exceeded their original mission of exploring the outer planets." Every bit of additional data is a bonus for heliophysics. The two probes have left the heliosphere of our sun - a kind of bubble in interstellar space that is largely formed by the solar wind.

The two probes are only more than 25 billion kilometers and 21 billion kilometers away from Earth respectively. Because of the distance, a radio signal takes 23 hours and 19.5 hours respectively to reach them.