Scientists evaluating recent data from NASA's Voyager and Cassini spacecraft have determined that Voyager 1 could cross over into the frontier of interstellar space anytime and a lot earlier than previously thought. The conclusions are detailed in a June Issue of the journal Nature.
Details from Voyager's low-energy charged particle instruments, first reported in December 2010, now have revealed that the outward velocity of the charged particles flowing from the sun has slowed to zero. The stagnation of this solar wind has persisted through at least February 2011, marking a thick, previously unforeseen "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 researcher 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Krimigis and colleagues combined the newest Voyager data with previously unpublished measurements from the ion and neutral camera on Cassini's magnetospheric imaging instrument. The Cassini instrument gathers data on neutral atoms surging into our solar system from the outside.
The research 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). Considering that Voyager 1 is already nearly 11 billion miles (18 billion kilometers) out, it could cross into interstellar space at any moment.
"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 just about 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.
Scientists plan to keep studying the Voyager 1 data, searching for confirmation. They will also be studying the Voyager 2 data, but Voyager 2 isn't as close to the edge of the solar system as Voyager 1. Voyager 2 is about 9 billion miles (14 billion kilometers) away from the sun.
Launched in 1977, the Voyager twin spacecraft have been on a 33-year quest. They are humanity's farthest working deep space sentinels enroute to reach the edge of interstellar space. The Voyagers were originally built by NASA's Jet Propulsion Laboratory in Pasadena, Calif., which will continue to operate both spacecraft. The Voyager missions are a part of the NASA Heliophysics System Observatory, subsidized by the Heliophysics Division of NASA's Science Mission Directorate in Washington. JPL is managed for NASA by Caltech.