Voyager 1 has crossed a new frontier, becoming the first spacecraft ever to leave the solar system, NASA said Thursday.
Thirty-six years after it was launched from Earth on a tour of the outer planets, the plutonium-powered probe is more than 11 .5 billion miles from the sun, cruising through what scientists call interstellar space — the vast, cold emptiness between the stars, the space agency said.
Search for proof of a dramatic exit
Voyager 1 actually made its exit more than a year ago, according to NASA. But it's not as if there's a dotted boundary line out there or a signpost, and there has been much debate in recent months over whether or not the probe had reached interstellar space. In August of last year it was believed Voyager had indeed reached the edge of our solar system, when charged particles streaming from the sun suddenly vanished and a spike in galactic cosmic rays burst in from the outside. But NASA scientists were not able to confirm that.
One key way to measure that would have been to monitor the density of the plasma around the probe. The plasma in our solar system is hotter and less dense than the plasma in interstellar space.
Unfortunately, Voyager's plasma measuring instrument failed in 1980, forcing scientists to look for an alternate way to confirm the probe's location.
The breakthrough happened when the sun burped up a solar blast, sending shockwaves throughout the solar system, which eventually reached Voyager. Plasma wave antennas on the probe vibrated when the waves reached them, indicating the probe was in fact in the colder, less dense plasma of interstellar space.
The vibrations were turned into a pitch and recorded on the spacecrafts internal tape deck. At the press conference Thursday, NASA's Voyager team played that tape for the public for the first time. It is the first recording ever from deep space.
Here's what deep space sounds like:
Since there was no detectable change in the direction of the magnetic field lines, the team assumed the far-flung craft was still in the heliosphere, or the vast bubble of charged particles around the sun.
The Voyager team patiently waited for a change in magnetic field direction — thought to be the telltale sign of a cosmic border crossing. But in the meantime, a chance solar eruption caused the space around Voyager 1 to echo like a bell last spring and provided the scientists with the data they needed, convincing them the boundary had been crossed in August of last year.
"It took us 10 seconds to realize we were in interstellar space," said Don Gurnett, aVoyager scientist at the University of Iowa who led the new research, published online in the journal Science.
Celebrations and cautious skepticism
Some scientists said they remain unconvinced, but that hasn't stopped NASA scientists from celebrating.
At NASA's Jet Propulsion Laboratory in Pasadena, Voyager project scientist Ed Stone said mankind has crossed a new threshold:
"Now that we have new, key data, we believe this is mankind's historic leap into interstellar space," said Ed Stone, based at the California Institute of Technology, Pasadena. "The Voyager team needed time to analyze those observations and make sense of them. But we can now answer the question we've all been asking -- 'Are we there yet?' Yes, we are."
NASA's also posted a video of the visibly-excited Stone and other members of the project team discuss the ramifications of Voyager's journey:
Voyager 1 will now study exotic particles and other phenomena in a never-before-explored part of the universe and radio the data back to Earth, where the Voyager team awaits the starship's discoveries.
The interstellar ambassador also carries a gold-plated disc containing multicultural greetings, songs and photos, just in case it bumps into an intelligent species.
Voyager 1's odyssey began in 1977 when the spacecraft and its twin, Voyager 2, were launched on a tour of the gas giant planets of the solar system. After beaming back dazzling postcard views of Jupiter's giant red spot and Saturn's shimmering rings,Voyager 2 hopscotched to Uranus and Neptune. Meanwhile, Voyager 1 used Saturn as a gravitational slingshot to power itself past Pluto.
Voyager 1, which is about the size of a subcompact car, carries instruments that study magnetic fields, cosmic rays and solar wind.
The new observations are fascinating, but "it's premature to judge," said Lennard Fisk, a space science professor at the University of Michigan and former NASA associate administrator who was not part of the team. "Can we wait a little while longer? Maybe this picture will clear up the farther we go."
What bothers Fisk is the absence of a change in magnetic field direction.
Harvard astrophysicist Jonathan McDowell was more blunt: "I'm actually not going to believe it for another year or two until it's been solidly outside for a while."
While Voyager 1 may have left the solar system as most people understand it, it still has thousands of years to go before bidding adieu to the last icy bodies that make up our neighborhood.
Voyager 2 trails behind at 9 1/2 billion miles from the sun. It may take another three years before Voyager 2 joins its twin on the other side. Eventually, the Voyagers will run out of nuclear fuel and will have to power down their instruments, perhaps by 2025.