In 2011, NASA was indicating that Voyager is close to the edge of the solar system.
Scientists analyzing recent data from NASA's Voyager and Cassini spacecraft have calculated that Voyager 1 could cross over into the frontier of interstellar space at any time and much earlier than previously thought. The findings are detailed in this week's issue of the journal Nature.
The Voyager-1 spacecraft was launched on September 5, 1977 and subsequently encountered Jupiter on March 5, 1979 and Saturn on November 12, 1980.
The Voyager-2 spacecraft was launched on August 20, 1977 and subsequently encountered Jupiter on July 9, 1979; Saturn on August 25, 1981; Uranus on January 24, 1986, and Neptune on August 25, 1989.
Both space craft are now traveling out of the Solar System in the "termination shock" phase of their interstellar mission. The trajectory of Voyager-1 is taking it toward the nose of the Sun's heliosphere above the ecliptic while the trajectory of Voyager-2 is taking it toward the nose of the Sun's heliosphere below the ecliptic.
Voyager 1 crossed the termination shock on December 16, 2004, and Voyager 2 crossed on August 30, 2007, on their way to the heliopause and interstellar space.
Nature - Zero outward flow velocity for plasma in a heliosheath transition layer
Data from Voyager's low-energy charged particle instrument, first reported in December 2010, have indicated that the outward speed of the charged particles streaming from the sun has slowed to zero. The stagnation of this solar wind has continued through at least February 2011, marking a thick, previously unpredicted "transition zone" at the edge of our solar system.
"There is one time we are going to cross that frontier, and this is the first sign it is upon us," said Tom Krimigis, prinicipal investigator for Voyager's low-energy charged particle instrument and Cassini's magnetospheric imaging instrument, based at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.
Krimigis and colleagues combined the new Voyager data with previously unpublished measurements from the ion and neutral camera on Cassini's magnetospheric imaging instrument. The Cassini instrument collects data on neutral atoms streaming into our solar system from the outside.
The analysis indicates that the boundary between interstellar space and the bubble of charged particles the sun blows around itself is likely between 10 and 14 billion miles (16 to 23 billion kilometers) from the sun, with a best estimate of approximately 11 billion miles (18 billion kilometers). Since Voyager 1 is already nearly 11 billion miles (18 billion kilometers) out, it could cross into interstellar space at any time.
"These calculations show we're getting close, but how close? 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," said Ed Stone, Voyager project scientist, based at the California Institute of Technology in Pasadena.
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