The possibility that the Voyager-1 spacecraft may have left the Solar System is being hotly debated.
Launched in September 1977, the probe was sent initially to study the outer planets, but then just kept on going.
Researchers studying its data say the craft appears now to be in a realm of space beyond the influence of our Sun.
But the US space agency (Nasa), which manages Voyager, says that it regards the probe as still being inside the Solar System.
The mission is currently moving more than 18 billion km from Earth, or 123 times the distance between our planet and the Sun.
The latest research is published online in the journal Geophysical Research Letters (GRL).
It concerns data the spacecraft has been gathering about changes in its environment which for some time now have suggested it is about to cross over the Solar System's border - the so-called heliopause.
more @ http://www.bbc.co.uk/news/science-environment-21866532