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Voyager 1 has left the Solar System

Charles Black, Founder and CEO of Sen
12 September 2013, 23:00 UTC

Sen— The Voyager 1 space probe has become the first human made object to leave the Solar System and is now travelling through interstellar space, according to new research.

The spacecraft, one of two identical probes launched in 1977, is now 18.8 billion kilometres (11.7 billion miles or 125 AU) from our Sun. A team of scientists led by Don Gurnett and the plasma wave science team at the University of Iowa have been studying data from Voyager 1 and calculated that the probe's first encounter with interstellar space was in August 2012.

Since then the probe has been travelling through the ionised gas that exists between the stars.

"Now that we have new, key data, we believe this is mankind's historic leap into interstellar space," said Ed Stone, Voyager project scientist at the California Institute of Technology. "The Voyager team needed time to analyze those observations and make sense of them. But we can now answer the question we've all been asking -- 'Are we there yet?' Yes, we are."

A massive ejection of solar particles in March 2012 provided the evidence scientists needed. When these particles caught up with Voyager 1 thirteen months later, in April 2013, the plasma around the probe began to vibrate. The spacecraft's plasma wave instrument detected the movement. From the pitch of the oscillations scientists were able to determine the density of the plasma and found the probe was travelling through plasma more than 40 times denser than it had encountered in the outer layer of the heliosphere (the bubble of charged particles around the Sun which stretches billions of kilometres beyond the outer planets) and that such density was expected in interstellar space.

The scientists examining the data also found a slightly fainter set of oscillations in October and November 2012. Calculating the plasma densities from both April 2013 and October/November 2012, the researchers concluded that Voyager 1 first entered interstellar space on August 25, 2012.

Don Gurnett explained: "We literally jumped out of our seats when we saw these oscillations in our data -- they showed us the spacecraft was in an entirely new region, comparable to what was expected in interstellar space, and totally different than in the solar bubble. Clearly we had passed through the heliopause, which is the long-hypothesized boundary between the solar plasma and the interstellar plasma."

Voyagers 1 and 2 illustartion

Voyager 1 and 2 are shown in this illustration at the edge of the heliosphere, the bubble created by solar wind. Credit: NASA/JPL-Caltech

“Voyager has boldly gone where no probe has gone before, marking one of the most significant technological achievements in the annals of the history of science, and adding a new chapter in human scientific dreams and endeavors,” said NASA's John Grunsfeld. “Perhaps some future deep space explorers will catch up with Voyager, our first interstellar envoy, and reflect on how this intrepid spacecraft helped enable their journey.”

Voyager 1 launched on September 5, 1977 whilst its twin, Voyager 2, launched first on August 20, 1977. Click here to read Mark Thompson's feature on the Voyager mission. The spacecraft are identical in design.

Voyager 1 flew by Jupiter and Saturn on its way out of the Solar System. Meanwhile, Voyager 2 flew by Jupiter, Saturn, Uranus and Neptune and is currently 15.4 billion km from the Sun. NASA says it won't be too long before the sister craft crosses the boundary to interstellar space.

Voyager 1 took the famous 'pale blue dot' image. In February 1990, when it was 6.4 billion km away, Voyager 1 turned its cameras on the planets and snapped the 'family portrait' showing Venus, Earth, Jupiter, Saturn, Uranus and Neptune. Missing from the picture were Mercury, which was too close to the Sun to be visible, whilst Mars showed only as a thin crescent of sunlight.

The Voyager mission is managed by NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. NASA believe the spacecraft will carry on going for many more years. Suzanne Dodd, Voyager project manager at JPL, said: "We expect the fields and particles science instruments on Voyager will continue to send back data through at least 2020. We can't wait to see what the Voyager instruments show us next about deep space."

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