Spacecraft reaches edge of solar system

A NASA space probe dispatched 33 years ago for the first close-up studies of Jupiter and Saturn has entered the tail of the solar system, a place where the constant stream of charged particles flowing from the sun ebbs. This final phase of solar system exploration should last another four years, computer models show, though scientists overseeing the two Voyager spacecraft really don't know what to expect.

Voyager 1 is now about 10.8 billion miles from the sun, traveling in a region of space known as the heliosheath, a turbulent area between the sphere of space influenced by the sun and magnetic forces from interstellar space that lies beyond.

In June, Voyager 1 relayed data that showed it was no longer traveling amongst the outward flow of solar wind particles. Instead, the solar stream has turned a corner, literally, as it sweeps, like an exhaust, into the tail of the heliosheath.

Flying along at about 38,000 mph, Voyager 1 is continuing its beeline toward interstellar space. It is so far from Earth that radio signals, traveling at the speed of light, take 16 hours to reach the spacecraft.

Its twin, Voyager 2, is traveling at a more leisurely 35,000 mph and will leave the solar system in a southerly direction a few years after Voyager 1, traveling in a northerly path, becomes the first human-made object in interstellar space.

Scientists hope to have five years for studies beyond the solar system before Voyager 1's plutonium power source is depleted.