There is a boundary to the Solar System. It exists in the spatial area where the sun's "bubble" of charged particles becomes less than the neutral atoms that stream into our star's system from outside said system. And the Voyager 1 spacecraft is about to cross that boundary -- sooner than scientists originally expected.
In an article in Nature revealing the findings of scientists monitoring the progress of the Voyager 1 and the Cassini spacecraft, data from Voyager's low-energy charged particle instrument, which has been collected since December 2010, indicates that the outward speed of charged particles that emanate from the sun has slowed to zero.
Tom Krimigis, prinicipal investigator for Voyager's low-energy charged particle instrument and Cassini's magnetospheric imaging instrument, and his colleagues at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., combined the data from the two spacecraft. Their analysis indicated that the boundary should exist somewhere from 11 billion to 14 billion miles out from the sun. Voyager 1 has traveled nearly 11 billion miles (which is the scientists' best estimate) thus far, so Krimigis believes that the boundary will soon be crossed.
"There is one time we are going to cross that frontier, and this is the first sign it is upon us," Krimigis said, according to PhysOrg.com.
Ed Stone, who is a Voyager project scientist, also looks forward to the "crossing" of the boundary. "These calculations show we're getting close, but how close?" he asked rhetorically. "That's what we don't know, but Voyager 1 speeds outward a billion miles every three years, so we may not have long to wait."
The scientists will study the incoming data from the two space probes until they get confirmation that the frontier has actually been crossed. Then they will know just how large an area the Solar System covers. And Voyager 1 will have entered into an interstellar trip, the first of Earth's spacecraft to leave the sun's territory.
Voyager 1 launched from Cape Canaveral, Florida, on September 5, 1977. The spacecraft was originally designed to study the gas giants Jupiter and Saturn, with its extended mission eventually taking it into interstellar space. It sent back data on Jupiter and its moons in 1979. A flyby of Saturn occurred in 1980.
As for the extended mission, Voyager 1 has been charged to ascertain and help map the edge of the Solar System, locate the edges of the Kuiper Belt, a massive asteroid-belt-like formation that surrounds the Solar System, and the heliosphere, which is the aforementioned charged particles "bubble" created in space by the sun's solar wind.
Voyager 2 is headed for the edge of the Solar System as well. However, it has only traveled 9 billion miles so far. It will take a few more years before it, too, crosses the "border" into interstellar space.
(photo credit: Harman Smith and Laura Generosa (nee Berwin), NASA.gov, Wikimedia Commons)