The Voyager-1 spacecraft has become the first manmade object to leave the Solar System. Scientists say the probe’s instruments indicate it has moved beyond the bubble of hot gas from our Sun and is now moving in the space between the stars.
Launched in 1977, Voyager was sent initially to study the outer planets, but then just kept on going. Today, the veteran Nasa mission is almost 19 billion km (12 billion miles) from home. This distance is so vast that it takes 17 hours now for a radio signal sent from Voyager to reach receivers here on Earth.
“This is really a key milestone that we’d been hoping we would reach when we started this project over 40 years ago – that we would get a spacecraft into interstellar space,” said Prof Ed Stone, the chief scientist on the venture. “Scientifically it’s a major milestone, but also historically – this is one of those journeys of exploration like circumnavigating the globe for the first time or having a footprint on the Moon for the first time. This is the first time we’ve begun to explore the space between the stars,” he told BBC News.
Sensors on Voyager had been indicating for some time that its local environment had changed. The data that finally convinced the mission team to call the jump to interstellar space came from the probe’s Plasma Wave Science (PWS) instrument. This can measure the density of charged particles in Voyager’s vicinity.Readings taken in April/May this year and October/November last year revealed a near-100-fold jump in the number of protons occupying every cubic metre of space. Edited from Voyager probe ‘leaves Solar System’.