'Important step in space exploration'
The Voyager-1 spacecraft has become the first man-made object to leave the solar system.
Launched in 1977, Voyager was sent initially to study the outer planets but eventually kept on its journey towards the outer limits of the solar system.
John Logsdon, professor emeritus at the Space Policy Unit at George Washington University, explained the significance of the event to Today programme's Justin Webb: "It's another step in space exploration, and potentially a very important one".
Paul Davies, Director of the Beyond Centre for Fundamental Concepts in Science at Arizona State University, explained that there are "obstacles" for humans to travel beyond the solar system: "It would certainly need some breakthrough technology."
First broadcast on the Today programme on Friday 13 September.