After a journey of 11 billion miles, the Voyager 1 spacecraft could be forgiven for asking the question: “Are we there yet?” Unfortunately for the probe, the answer is no. Launched in the summer of 1977, the spacecraft Voyager 1 and Voyager 2 have been travelling in space for more than 35 years. They hold the record for being the man-made objects that have travelled the furthest.
The primary mission was supposed to last just five years but it is a project that just keeps giving. Even now, data coming back from Voyager 1 is redefining our thoughts on what makes up the edge of the solar system. (Although Voyager 2 was launched first, it has been overtaken by its sister craft and is currently in a semi-dormant state.)
As Voyager 1 heads for outer space, part of the challenge is how to define what the “edge” of the solar system is (its limit is usually agreed to be where the sun’s influence ends). At a distance of 11 billion miles, Voyager 1 now feels the effect of the sun mainly through its magnetic field and the solar wind – a stream of energetic particles flowing through space that originated from the sun’s surface. These particles form a sort of envelope around the solar system, known as the “heliosphere”. In August 2012, Voyager entered a region where these solar winds increased in speed and where high-energy particles from outside the solar system are also entering the heliosphere via interstellar magnetic fields.
Edward Stone, the current Voyager project scientist, says: “Voyager 1 still is inside the sun’s environment. We can now taste what it is like on the outside, because the particles are zipping in and out on this magnetic highway.” Models had not predicted this intense magnetic region. Stone adds: “The new region isn’t what we expected but we’ve come to expect the unexpected from Voyager.” That sentiment seems to sum up the mission to date.