We've made it to the stars, at last.
For the first time, a human-made object has left the sun's realm behind and ventured into the vast space between the stars, scientists announced Thursday. The record-setting spacecraft is NASA's scrappy Voyager 1, which launched in 1977 and edged into interstellar space on Aug. 25, 2012, according to recent data.
"We are in a new region of space where nothing has been before," says Voyager project scientist Ed Stone of Caltech.
Voyager's feat is a first, but the claim that it has finally tiptoed past the border to interstellar space is not. For a decade, researchers have trumpeted the spacecraft's arrival at one new cosmic boundary after another. In March, scientists presented data arguing that the ship had reached interstellar space in August 2012.
NASA promptly poured cold water on the claim. Stone declared it was "critical" to detect certain changes in the magnetic field before concluding that Voyager had departed the heliosphere. That's the enormous blob of solar particles that envelops the planets and shields them from galactic radiation; outside the heliosphere lies the dark, chilly space between stars.
There have been no published reports of the magnetic-field changes that Stone sought as confirmation. Even so, he says he and most of his colleagues think the spacecraft has made it. The clinching evidence is the result of extraordinary good luck: In March 2012, a huge storm on the sun caused vibrations in the soup of charged particles through which Voyager was traveling.An instrument on the spacecraft measured the vibration, and researchers report in this week's Science that the vibration is not at all what they'd expect from the charged particles in the heliosphere. Instead, the vibration is characteristic of a different type of charged particle - those found in interstellar space.
The paper's authors dug up records from other such vibration episodes, then put all of the data together to infer when Voyager must have hit the edge of the heliosphere. The answer was Aug. 25, 2012 - the same date that Voyager's sensors recorded the near-disappearance of a type of cosmic ray found inside the heliosphere and a dramatic spike in a type of cosmic rays from outside the solar system.
"All the facts, the actual data, are consistent with having crossed (into interstellar space) on or around Aug. 25," says the University of Iowa's Donald Gurnett, an author of the Science paper.
Aug. 25, 2012, is also the date that NASA downplayed earlier this year. This time, though, the agency is on board. Thanks to the new vibration data, "most of us believe we're in interstellar space," Stone says.
Still, Stone says it's not correct to say the spaceship has left the solar system. He points out that Voyager has not yet passed the Oort cloud, a source of comets that is also the outermost edge of the solar system.
The findings provide strong evidence that Voyager has left the solar bubble, but it would be better if the spacecraft had seen the telltale magnetic-field change, says space physicist David McComas of the Southwest Research Institute in San Antonio."Then it would have been definitive, no questions at all," he says.
Other scientists are pretty much convinced already. The vibrations seen by the spacecraft could have been made only in the interstellar medium, says Boston University space physicist Merav Opher.
The historic crossing is "extremely dramatic and very romantic," she says, but also "bittersweet. ... I wish Voyager 1 could've stayed longer" at the brink of interstellar space. "Such a pity it left. I wanted more data."