Voyager 2 reaches interstellar space

Michele Stevens
December 13, 2018

The probe has now journeyed past the "heliopause" which marks the boundary between the solar system and interstellar space.

The plasma-measuring device that verified Voyager 2's exit on November 5 - and remains broken on Voyager 1 - will now offer unique data on the heliopause, where dwindling solar wind gives way to the interstellar medium. It takes almost 17 hours for a radio signal, traveling at the speed of light from Earth, to reach Voyager 2 - as a comparison, it takes a little more than eight minutes for light to travel from the sun to Earth. By comparison, light traveling from the Sun takes about eight minutes to reach Earth.

The first device in history that left the heliosphere, was the "Voyager-1".

The approximate positions of Voyager-1 and 2. PLS uses electrical currents of plasma emitted by the Sun to detect speed, density, temperature, pressure and flux of solar winds inside the Heliosphere.

The milestone actually took place on November 5 when Voyager crossed the outer edge of the heliosphere, the protective bubble of particles and magnetic fields created by the Sun.

"It was about a month's worth of checking to make sure the universe wasn't playing tricks on us", Mr Nagle said.

It's trailing twin Voyager 1, which reached interstellar space in 2012 and is now 13 billion miles from Earth.

So to be sure that Voyager 2 left the heliosphere, NASA leaned on data from five instruments.

"I often get asked, 'So, is this it for Voyager?".

Voyager 2 exits the heliosphere
Voyager 2 Enters Interstellar Space

"All the stars in the solar neighbourhood are in an orbit around the centre of the Milky Way, with orbital periods of 225 to 250 million years", says Voyager project scientist Ed Stone.

But what's next for the two Voyagers? Where this boundary ends, interstellar space begins.

The two plutonium-powered spacecraft, launched in 1977 to make a tour of the giant planets, are still operational and continue to explore.

"Our sun pumps out energy in all directions known as solar wind and that energy streaming out collides with all of the energy coming in", Mr Nagle explained. Sadly the spacecraft won't still be sending us data at that point. But it hasn't left the Solar System, according to the release-it has yet to enter the hypothetical Oort cloud of objects still influenced by the Sun's gravity.

The Oort Cloud starts around 150 billion kilometres from the Sun and extends out to about 30 trillion kilometres.

The spacecraft, powered by radioisotope thermoelectric generators (RTGs), are gradually losing power as their plutonium power sources decay.

Voyager 2 is now out there among the stars, and it should still work for a few more years. "This is what we've all been waiting for".

After both studying Jupiter and Saturn-with Voyager 2 taking a detour to also visit Uranus and Neptune-the two probes continued their journeys toward the edge of the solar system. An instrument called the Plasma Science Experiment (PLS), which stopped working on Voyager 1 well before leaving the heliosphere, continues to operate on Voyager 2 - making it easier for scientists to learn about the spacecraft's surroundings.

NASA's Voyager 2 is probing the space between the stars.


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