Voyager 2 breaks through solar bubble to join its twin in deep space

11 Dec 2018

Artist’s concept of the Voyager spacecraft in space. Image: NASA

The Voyager 2 spacecraft has now gone where only one other spacecraft has gone before, and it happens to be its twin.

After completing what amounted to the scenic route of the planets of the solar system, NASA’s Voyager 2 spacecraft recently announced to its home planet that it has finally left the sun’s influence.

Despite being more than 40 years old and with processing power only a fraction of what exists on modern smartphones, Voyager 2 was still able to send back data showing it has exited the heliosphere, the protective bubble of particles and magnetic fields created by the sun.

Estimates put the date of 5 November as when it finally broke the historic barrier, becoming only the second spacecraft to do this. In 2012, Voyager 1 achieved the same feat, despite the fact it launched 16 days after Voyager 2 in 1977.

This was because the planned route for Voyager 2 was significantly longer, with it being set on a flyby course with many of the outer planets, revealing the first close-ups and important scientific data on planets such as Saturn, Neptune and Uranus.

The point at which Voyager 2 broke the barrier is called the heliopause, where tenuous, hot solar wind meets the cold, dense interstellar medium, putting it more than 18bn km from Earth. Despite this, NASA will still be able to communicate with the spacecraft as it continues its path into deep space, but each communication with it takes about 16.5 hours to send.

Nowhere near leaving the solar system

The most compelling evidence of Voyager 2’s exit from the heliosphere came from its onboard Plasma Science Experiment (PLS), an instrument that stopped working on Voyager 1 in 1980, long before that probe crossed the heliopause.

The PLS uses the electrical current of the plasma to detect the speed, density, temperature, pressure and flux of the solar wind. However, on 5 November, the instrument went silent, showing it had exited the bubble.

Despite it leaving the heliosphere, Voyager 2 won’t be leaving the solar system any time soon, with the outer edge being beyond the Oort Cloud, a collection of small objects still under the influence of the sun’s gravity. While its width isn’t exactly known, it is estimated to begin at about 1,000 astronomical units (AU) from the sun and to extend to about 100,000 AU.

By that estimate, it will take another 300 years for the spacecraft to reach the inner Oort Cloud, and as many as 30,000 years to fly past it.

“Voyager has a very special place for us in our heliophysics fleet,” said Nicola Fox, director of the heliophysics division at NASA. “Our studies start at the sun and extend out to everything the solar wind touches. To have the Voyagers sending back information about the edge of the sun’s influence gives us an unprecedented glimpse of truly uncharted territory.”

The journeys of both Voyager 1 and Voyager 2 were recently charted by the Irish-made, award-winning documentary The Farthest.

Colm Gorey was a senior journalist with Silicon Republic