Voyager 1 at Solar System's Edge; When Will It Cross Threshold?

Forget Captain Kirk's USS Enterprise. NASA's Voyager 1 probe continues to boldly go where no probe has gone before.

Experts appear to have found a new area at the edge of our solar system and may be close to jettisoning the 35-year-old spacecraft into space, according to experts.

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Voyager 1 had an abrupt drop in the number of solar particles hitting its detector last August and a big jump in cosmic rays from other places in the galaxy, according to scientists in three studies in the journal Science published June 27.

Because Voyager 1 didn't record a directional shift in the ambient magnetic field, researchers concluded that it remains within the sun's gravitational pull. Still, mission scientists think the probe is destined to depart the Earth's solar system.

Ed Stone, a Voyager project scientist and lead author of one of the new studies, said the probe will make the pilgrimage within the next few years.

"I think it's probably several more years — 2015 is reasonable," Stone said. "But it's speculation, because none of the models we have, have this particular region in them. So none of the models can be directly and accurately compared to what we're observing. What we're observing is really quite new."

Voyager 1 and its twin, Voyager 2, were launched in 1977 for a "Grand Tour," which benefitted from a favorable positioning of the giant gas planets that occurs less than once a century. 

Voyager 1 cruised by Jupiter and Saturn before heading north. Voyager 2 swung by Jupiter and Saturn, then Uranus, and Neptune before heading south. The spacecrafts were able to collect thousands of pictures for scientists to study.

Currently, Voyager 1 is about 11.5 billion miles from the sun, while Voyager 2 is about 2 million miles closer. The nuclear-powered craft can power its instruments until sometime in 2020, according to The Canadian Press.

Scientists haven't determined the density of this newfound region or when Voyager 1 will break through to the other side.

"It could actually be anytime or it could be several more years," Stone said.

Mission scientists will continue to monitor Voyager's magnetic-field readings in the coming years.

"If there's a dramatic change, like there was last Aug. 25, that will be very exciting," Stone told SPACE.com. "If it's a gradual change, well, it'll just take us longer to realize what's happening."

These spacecraft contain a heat-generating power supply from radioactive decay of plutonium-238, and thrusters are occasionally fired to keep the ship's radio antenna pointed toward Earth. Stone estimates that the declining power will force scientists to begin shutting down some of its instruments in 2020. The last instrument will likely be turned off in 2025, barring any unforeseen complications.

"It changed the way we view our place in the cosmos," Bill Nye, who is chief executive of the Planetary Society in Pasadena, Ca., told the Washington Post. "What are you going to find over the unknown horizon? We don't know. That why we explore out there."

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