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Year in Review: Voyager 1 reaches interstellar space

Planetary probe is first to pass beyond heliosphere

GOING THE DISTANCE  Voyager 1 is the first human-made object to break out of the heliosphere.

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When Caltech’s Ed Stone watched the launches of Voyager 1 and Voyager 2 from Cape Canaveral in 1977, he had only a glimmer of hope that either probe would survive to reach interstellar space. “The space age was only 20 years old,” says the missions’ principal investigator. “We had no idea how long spacecraft could last.”

Thirty-six years later, Stone announced that Voyager 1 had become the first human-made object to pass beyond the heliosphere, the giant invisible bubble inflated by subatomic particles from the sun, and enter the space between the stars (SN Online: 9/12/13). Based on measurements from the probe’s instruments, Voyager made its exit in August 2012.

But only in September of this year did Stone and his team, many of them original Voyager scientists, decide that they had enough evidence to confirm the crossing. The announcement carried a sense of déjà vu because multiple scientists had made the case in previous months that the milestone had been reached.

Now astronomers are digging into the probe’s latest observations, the first from a region of space teeming with speedy protons and electrons expelled in the violent explosions of distant stars. Scientists have studied plenty of these particles with space-based detectors, but never in a pristine environment largely free of radiation and magnetic interference from the sun. “We’re left with decades of interesting work ahead of us,” says Gary Zank, a space physicist at the University of Alabama in Huntsville. 

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