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© NASAThe Voyager 1 spacecraft.
The Voyager 1 spacecraft moves through uncharted territory, literally, on a daily basis, moving through space and sending back collected data to researchers on Earth. But a recently discovered anomaly has been discovered at the edge of the Solar System. Could it pose a problem with Voyager 1's mission?

Voyager 1, the spacecraft launched 33 years ago to observe the largest planets circling the sun, is set to pass out of the Solar System within the next few years. It has entered what scientists refer to as the heliosphere, which is the outer border of the sun's charged particle influence. Data streaming back from both Voyager 1 and Voyager 2 revealed that the border with interstellar space, however, isn't a smooth "transition zone" as was theorized. Instead, the border appears to be made up of "magnetic bubbles." Given the effects of magnetism on electromagnetic working systems, could the newly discovered "bubbles" pose a risk to Voyager 1's interstellar mission? Fortunately for Voyager 1 and her trailing sister craft, Voyager 2, the answer is "no."

Caltech professor Edward C. Stone, Voyager project scientist and former director of the Jet Propulsion Laboratory, offered reassurance in an interview in early June. "The spacecraft are unaware of all this," he said. "From a spacecraft point of view, this is a better vacuum than anything here on Earth in a laboratory. Only our sensitive instruments will tell us when the direction and the speed of the wind has changed, and when the direction of magnetic field and its strength have changed."

Most of the evidence for the existence of the "bubbles" comes from readings from an energetic particle-sensing instrument aboard the Voyager spacecraft. Using collected data, researchers were able to construct models of the outer limits of the Sun's magnetic field. The magnetic bubbles are believed to be 100 million miles wide (the distance between the Earth and the Sun) and sausage-shaped.

"The sun's magnetic field extends all the way to the edge of the solar system," explained astronomer Merav Opher of Boston University, who contributed, with Maryland University's Jim Drake on the published findings of the Voyager data in Astrophysical Journal. "Because the sun spins, its magnetic field becomes twisted and wrinkled, a bit like a ballerina's skirt. Far, far away from the sun, where the Voyagers are, the folds of the skirt bunch up."

But the bunching-up effect remains far too weak to effect the workings of the Voyager spacecraft, allowing the interstellar-bound craft to continue on its way virtually without interference.

Voyager 1 crossed the "termination shock" area of the heliosphere and entered the heliosheath in December 2004. Researchers believe that it is now in a "transition zone" of indeterminate size. Data collected from the two Voyager craft and the Cassini spacecraft indicate that charged solar particles in Voyager 1's region have reached a velocity of zero. Allowing for a particular quiet solar period (solar wind activity is currently experiencing a lull), scientists are studying data to determine if the craft has indeed reached the edge of the Solar System. When the presence of particles from the Milky Way begin to exceed those projected outward from the Sun, a border area called the heliopause, the craft will have made its crossing into interstellar space.

"We're getting very close, because we know the outward motion of the solar wind now has gone to zero - it's not going outward anymore," Stone said. He added that the crossing into interstellar space "could happen any day, or it could happen in two, three years. Our models are not accurate enough to be able to tell us that, because we keep learning new things - like maybe there are bubbles out there."

Voyager 1 and Voyager 2, both launched in 1977, were initially designed to explore the Solar System's larger planets. However, as the spacecraft were still in good working condition and able to transmit data, NASA instituted a secondary mission, the Voyager Interstellar Mission, once Voyager 2 completed its flyby of Neptune in 1989. The mission has three phases: exploration of the the termination shock, heliosheath exploration, and interstellar exploration phases.