Two pioneering space probes are reaching the edges of the solar system 30 years after they were launched.

Voyager 2, launched in August 1977, is still sending data back to Earth from a distance of 7.8 billion miles (12.6 billion km).

Its sister ship, Voyager 1, launched in September 1977, is even farther away at 9.7 billion miles (15.6 billion km), making it the most distant man-made object in space.

In their first 12 years of flight the two spacecraft sent back close-up pictures of Jupiter, Saturn and their moons, plus the first detailed images of Uranus and Neptune. For the past 19 years they have been approaching the limits of our solar system, where the Sun’s influence ends and interstellar space begins.

In December 2004 Voyager 1 entered the part of this boundary called the heliosheath, approximately 8.7 billion miles (14 billion km) from the Sun. The solar wind slows as it crashes into the thin gas that fills the space between stars. Voyager 2 is expected to reach this boundary later this year.

Each spacecraft carries five fully functioning science instruments that study solar wind, energetic particles, magnetic fields and radio waves as they cruise through this region.

The spacecraft are too far from the Sun to use solar power. Instead, they run on less than 300 watts, enough to power a bright light bulb, which is provided by radioisotope thermoelectric generators.

Alan Stern, associate administrator for Nasa’s Science Mission Directorate, in Washington, said: “It’s a testament to Voyager’s designers, builders and operators that both spacecraft continue to deliver important findings more than 25 years after their primary mission to Jupiter and Saturn concluded.”

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