Official: Voyager 2 is now an interstellar spacecraft

The veteran probe that keeps going has now gone where only Voyager 1 has gone before

Voyager probe illustration

NASA’s Voyager 2 probe has followed its sibling, Voyager 1, into interstellar space, according to the team managing the veteran spacecraft.

Voyager 1 exited the heliosphere – the bubble of particles and magnetic fields created by the Sun that surrounds the solar system – back in 2012, although it took the best part of a year for boffins to actually confirm the findings.

For Voyager 2 things are a bit more straightforward, not least because Earthbound boffins now know what to look for. Voyager 2 also has the benefit of a functioning Plasma Science Experiment (PLS) instrument. The one on Voyager 1 stopped working back in 1980.

The PLS uses the electrical current of the plasma flowing out from the Sun to detect the solar wind. Back on 5 November, Voyagers 2's PLS observed a sudden, dramatic decline in the speed of solar wind particles. Since that date, the instrument has detected no solar wind flow around the aging probe, making scientists confident that Voyager 2 had indeed left the heliosphere and entered interstellar space.

The team also used data from three other instruments still running on board the probe – the cosmic ray subsystem, the low energy charged particle instrument and the magnetometer – to confirm that Voyager 2 has, in a very real sense, left the building.

Voyager 2 is currently just over 18 billion kilometres from Earth, with information taking about 16.5 hours to reach the spacecraft.

As for actually leaving the solar system itself, well – probably best not to hold your breath. Depending on your definition, the outer edge of the solar system is considered to be the Oort Cloud, a collection of objects still under the influence of the Sun's gravity. The Voyagers should get there in about another 300 years and boffins reckon it could take as long as 30,000 years to actually fly through it.

The Reg chats with Voyager Imaging Team member Dr Garry E Hunt

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Of course, the Voyagers will be long dead by then. The power output of the onboard Radioisotope Thermal Generators (RTG) used to keep the spacecraft ticking over declines by around about four watts per year. This means that, over 40 years after launch, scientists are shutting down instruments in order to eke the power out for as long as possible.

The spacecraft were originally specified to last five years, but canny design choices by talented engineers, as well a brilliant ground team, have kept the Voyagers running long after the warranty has expired. Voyager 2 could keep transmitting data until 2025 – nearly 50 years after launch – before there won’t be enough power left to run any instruments.

Member of the original Voyager imaging team, Dr. Garry Hunt, told The Register that he was "stunned" that nearly 50 years since work began on the project, the probes were still running and doing useful science. "Discoveries," Hunt told us, "are still being made from data sent back by the probes", which is, of course, publicly available.

"It is a joy that they persevere as messengers," said Hunt, before paying tribute to engineers that "made it happen, and happen, and still happen" after all these years. ®

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