Over 30 years after it was launched, NASA’s Voyager 2 space probe has reached the “edge” of the solar system.

In doing so the probe has confirmed that the heliosphere — an immense bubble-like structure surrounding the Sun and formed by the solar wind — is not a perfect sphere but is a squashed ellipsoid.

Voyager 2 crossed the “heliospheric termination shock” in August 2007 at a distance of about 12bn kilometers from the Sun. This is about twice as far from the Sun as Pluto and about 1.5bn kilometers closer to the Sun than where its partner Voyager 1 crossed this threshold in 2004. This confirms telescope-based observations of the flow of hydrogen and helium in this region made in 2005, which suggested that the heliosphere is squashed by interstellar magnetic fields.