NASA probe becomes second craft ever to enter interstellar space

Voyager 2 has left behind the solar winds encompassing our sun and will now give us a glimpse into "truly uncharted territory." The NASA space probe is the second human-made object in history to pass this milestone.

Over 40 years after it left planet Earth, the Voyager 2 space probe has crossed over into interstellar space, NASA announced on Monday.

The US space agency said that the spacecraft has exited the outer boundary of the heliosphere — the bubble of solar wind that the sun creates around itself — in early November.

Voyager 2 is now some 11 billion miles (about 18 billion kilometers) from Earth and is the second human-made object to pass into the vast area of interstellar space.

NASA was able to determine Voyager 2's position based on data gathered from one of its key instruments — a Plasma Science Experiment (PLS). The instrument recorded a steep drop in the speed of solar wind particles on November 5 and hasn't recorded any solar wind flow since.

Its twin probe, Voyager 1, was the first to cross into interstellar space in 2012, although its PLS instrument stopped working decades ago.

Both the Voyager 1 and Voyager 2 launched from the US in 1977

'Unprecedented glimpse' into interstellar space

Nicola Fox, director of the Heliophysics Division at NASA Headquarters, said in a statement that the Voyager probes have a "special place" in her department.

"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," she added.

Both the Voyager 1 and Voyager 2 launched from the US in 1977 and have carried out flyby missions on Jupiter, Saturn, Uranus and Neptune — extending long past their five-year lifespans.

Mission operators are still able to communicate with Voyager 2, although it currently takes 16.5 hours for information to travel from the probe back to Earth since the data is moving at the speed of light.

"By comparison, light traveling from the Sun takes about eight minutes to reach Earth," NASA said in its statement.

Voyager 1 and 2: NASA spacecraft on tour for 40 years and counting

Two sister probes

On August 20th 1977 NASA lauched Voyager 2 for a record flight that is still going. Shortly after, on September 5th, the identically built Voyager 1 followed. The initial aim of the mission was to obtain more information about Jupiter and Saturn, planets which were still largely unexplored at the time. Thanks to the long-lasting plutonium batteries, both spacecraft are still active.

Voyager 1 and 2: NASA spacecraft on tour for 40 years and counting

Staying power

Weighing 825 kg or 1,818 pounds (on Earth), the Voyager probes are among NASA's biggest success stories. Both still regularly send reliable data from space. They're moving farther and farhter away from Earth, but the radio connection is expected to work until 2030.

Voyager 1 and 2: NASA spacecraft on tour for 40 years and counting

Leaving the solar system

On August 25th 2012 Voyager 1 crossed the heliopause, one of the borders of our solar system. There, the interstellar space of our galaxy - the Milky Way - beginns. Voyager 1 is the man-made object most distant from Earth - currently at about 139 times the distance between Earth and Sun.

Voyager 1 and 2: NASA spacecraft on tour for 40 years and counting

Flight routes

The solar system has different borders: The first is the "termination shock." That's where the solar winds slow down dramatically. After the heliosphere comes the heliopause. That's the edge of the space bubble where solar flares shield us from interstellar rays. NASA measured a 40 times higher plasma density after Voyager 1 crossed the heliopause.

Voyager 1 and 2: NASA spacecraft on tour for 40 years and counting

Big planet, lots of pictures

There was a lot the spacecraft has discovered so far: Voyager 1 sent back this image of Jupiter on January 1, 1979. In all, Voyager 1 took a total of 17,477 images of the planet and four of its moons. The existence of the thin ring system surrounding Jupiter was detected for the first time through these images.

Voyager 1 and 2: NASA spacecraft on tour for 40 years and counting

Detailed photos

Voyager 1 also documented atmospheric flows on Jupiter, as seen in this picture. After the Jupiter flyby, Voyager 1 reached a speed of 16 kilometers per second.

Voyager 1 and 2: NASA spacecraft on tour for 40 years and counting

True colors

Voyager 2 sent this full-color photo of Saturn back to Earth. The probe reached the sixth planet in our solar system in 1981. In outer space terms, this photo is a real close-up: it was taken from a distance of just 21 million kilometers (about 13 million miles).

Voyager 1 and 2: NASA spacecraft on tour for 40 years and counting

Everything under control

The distant probes are monitored and controlled, as far as that's possible, by the control center of the Voyager mission at the California Institute of Technology in Pasadena, seen here in 1980. Today, the equipment is much more modern. But NASA regularly has to consult with the engineers who designed and built the Voyager spacecraft - even though they have long been in retirement.

Voyager 1 and 2: NASA spacecraft on tour for 40 years and counting

Sounds of Earth for alien ears

In the event the probes encounter life on their endless journey, they have these gold discs along for the ride. The record contains pictures and sounds of people, animals and nature on Earth. In case the aliens don't own a record player, a needle and picture instructions are provided.

Voyager 1 and 2: NASA spacecraft on tour for 40 years and counting

Space art

For decades, the Voyager missions have not only fascinated space fans - even artists have been inspired. In 1977, just before the launch, an anonymous American artist imagined the Voyager 1 Saturn flyby.

Not leaving solar system soon

NASA estimates that the probes could last another five to 10 years, but the extreme cold outside the vehicles and their waning power supply means they will eventually become less useful, said Voyager project manager Suzanne Dodd.

"I think we're all happy and relieved that the Voyager probes have both operated long enough to make it past this milestone," Dodd said.

Both of the spacecraft are still technically in our solar system, as they have yet to pass beyond it's outer edge known as the Oort Cloud.

It could be another 30,000 years before they would fly beyond it and come close to other stars, NASA said.

In the meantime, the probes are still sending crucial information back to Earth about the area beyond the heliosphere — and the space between the stars.

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