The Voyager-1 probe has left the Solar System, according to some scientists. If confirmed, it would be the first man-made object to do so. Launched in September 1977, the probe was sent initially to study the outer planets, but then just kept on going.
Researchers who have studied its data indicate it has now entered a realm of space beyond the influence of our Sun. But the US space agency (Nasa) says there is still some doubt about this.
Voyager is currently moving more than 18 billion km from Earth, or 123 times the distance between our planet and the Sun. The claim is made in a soon-to-be published paper in the journal Geophysical Research Letters.
The spacecraft has been monitoring changes in its environment for some time that have suggested it is about to cross the Solar System's border - the so-called heliopause.
It has been detecting a rise in the number of high-energy particles, or cosmic rays, coming towards it from interstellar space, while at the same time recording a decline in the intensity of energetic particles coming from behind, from our Sun.