Has Voyager 1 left the solar system?
Telltale change in cosmic radiation at issue
Scientific confusion was the order of the day on Wednesday following a report that suggested a 35-year-old space probe had become the first human-made object to make it beyond our solar system.
New Mexico State University astronomer W.R. Webber reported in a paper published online by the American Geophysical Union that the spacecraft had made it beyond the influence of the sun because Voyager 1 had measured a drastic change in radiation levels last Aug. 25.
But no sooner had that report appeared than NASA said it begged to differ with any interpretation that suggested that its spacecraft had definitely left the solar system.
"The Voyager team is aware of reports today that NASA's Voyager 1 has left the solar system," said Edward Stone, Voyager project scientist based at the California Institute of Technology, Pasadena, Calif. "It is the consensus of the Voyager science team that Voyager 1 has not yet left the solar system or reached interstellar space."
Stone said the Voyager team reported last December that Voyager 1 was within a region called 'the magnetic highway' where energetic particles changed dramatically. "A change in the direction of the magnetic field is the last critical indicator of reaching interstellar space and that change of direction has not yet been observed," Stone said.
The American Geophysical Union subsequently revised the "left-the-solar-system" headline on its news release with a less dramatic one that said Voyager 1 had "entered a new region of space."
Webber's research suggested that when the spacecraft was roughly 18 billion kilometres from the sun last Aug. 25, it suddenly nearly stopped detecting "anomalous" cosmic rays. That is a type of radiation trapped in the outer part of the heliosphere, the vast "bubble" of space affected by the sun's magnetic field, which encloses the solar system.
Meanwhile, he said the spacecraft had detected record levels of "galactic" cosmic rays, radiation that comes from outside the solar system.
Webber said it's not clear whether Voyager 1 has actually entered interstellar space or some other zone beyond the solar system.
"It's outside the normal heliosphere, I would say that," Webber said in a statement. "We're in a new region. And everything we're measuring is different and exciting."
Earlier false alarm
Voyager 1 had also detected a number of temporary changes in radiation starting July 28 and August 14 that had generated other "false alarms" of its departure from the solar system.
During those times, Voyager 1 may have crossed some kind of boundary at the edge of the heliosphere "at least five times." However, it wasn't clear if that happened because the boundary itself was moving or because the edge of the heliosphere contains "ribbons" of radiation connected to the region beyond the heliosphere.
Voyager 1 was launched from Cape Canaveral, Fla., on Sept. 5, 1977, two weeks after its twin, Voyager 2. Voyager 1 made its closest approaches to Jupiter and Saturn on March 5, 1979, and Nov. 12, 1980, respectively.
Voyager 2, which also made close approaches to Uranus and Neptune, is about three billion kilometres behind Voyager 1.