Andrew Masterson
Andrew Masterson is a former editor of Cosmos.
NASA’s Voyager 2 probe, launched just over 40 years ago, looks set to become the second human-made object ever to leave the solar system.
Voyager team members report that since August this year two devices aboard the probe – the Cosmic Ray Subsystem instrument and the Low-Energy Charged Particle instrument – have both measured a 5% increase in the amount of cosmic rays being detected.{%recommended 7580%}
While not definitive, the results strongly suggest that Voyager 2 is about to reach the limits of what cosmologists called the heliosphere – the area of local space dominated by solar material and magnetic fields.
The edge of this vast sphere is called, logically enough, the heliopause. Cosmic rays comprise high speed nuclei, mostly hydrogen, or electrons that originate from beyond the solar system. An increase in the number smashing into the probe is thus pretty good evidence that the craft is moving towards the edges of the sun’s protection.
The findings also correlate with similar results recorded by Voyager’s sister craft, Voyager 1, in May 2012 – about three months before it became the first manufactured artefact to leave the solar system.
“We’re seeing a change in the environment around Voyager 2, there’s no doubt about that,” says project scientist Ed Stone, based at Caltech in Pasadena, US.
“We’re going to learn a lot in the coming months, but we still don’t know when we’ll reach the heliopause. We’re not there yet – that’s one thing I can say with confidence.”
Voyager 2 was launched in 1977. It is currently about 17.7 billion kilometres from Earth – more than 118 times the distance between the Earth and the sun.
