Has Voyager 1 Space Probe Left Our Solar System?

Stefan Lovgren
for National Geographic News
November 5, 2003

It's been a record-shattering ride for the Voyager 1 spacecraft since it was launched in 1977. It returned the first spacecraft photographs of Earth and moon. It visited both Jupiter and Saturn. Five years ago, it became the most distant human-made object in space.

Now, after traveling 13.5 billion kilometers (8.4 billion miles), it may have already exited the solar system altogether.

A team of scientists says that Voyager 1 last year encountered a drop in the solar wind speed, suggesting it had reached the transitional region between our solar system and interstellar space.

However, another group of scientists maintains that Voyager 1 is near the "termination shock," the boundary of our solar system where the solar winds change from supersonic to subsonic flow, but has not yet crossed into it.

Either way, Voyager 1 is charting unexplored territory.

"It's the first time a human-made object has been flirting with the boundary between our solar system and interstellar space," said Stamatios Krimigis, head of the space department at Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, who is leading the team of scientists arguing that Voyager 1 already exited our solar system. "We're getting out of the cocoon of solar influence."

The research is described in tomorrow's issue of the science journal Nature.

On the Edge

The Voyager 1 and 2 missions blasted off from Earth in 1977. Their visits to Jupiter in 1979 and Saturn in 1980 greatly expanded our knowledge of those outer planets. Voyager 2 is the only spacecraft to visit Uranus and Neptune.

Voyager 1, which is traveling at a speed of 17 kilometers per second (38,000 miles per hour) is now exactly 90 astronomical units from the sun. (One astronomical unit equals the distance between the Earth and the sun.)

That's about twice as far from the sun as Pluto, the ninth planet in the solar system. Voyager 2, which is not traveling as fast as its twin, is about 80 percent as distant as Voyager 1.

In this region, the solar-wind plasma starts to merge with the plasma of the interstellar medium beyond the solar system. This begins with a boundary—known as the termination shock—where solar wind speeds abruptly drop from supersonic to subsonic, similar to the shock that precedes a supersonic plane that causes a sonic boom.

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