Voyager 1 and 2 have been in space for 33 years and have traveled 11.5 billion and 9.5 billion miles respectively.
Not knowing where we are makes us all a little crazy. Consider how you feel when you’re driving along a strange road without a map or a GPS. Consider how you feel when you’re on the street in a city overseas, having no idea how to get back to your hotel and you don’t speak the local language. There’s a reason people freaked out when Apple dropped Google Maps. There’s a reason airplane seatbacks have little route maps on the screen. It takes a solid sense of place, it seems, to give us a solid sense of safety.
So pity the scientists tracking the Voyager 1 spacecraft.
As most people who pay attention to these things noticed yesterday, there was a cosmic battle royal when the American Geophysical Union (AGU) issued a surprise press release about new Voyager readings with the stunning headline: “Voyager 1 has left the solar system, sudden changes in cosmic rays indicate,” making it the first human-built object to cross that remarkable threshold. But NASA, which knows a thing or two about the twin Voyager spacecraft since it built them, launched them and controls them, fired back with a press release that said, in effect: Not. The NASA release tersely quoted the venerable Ed Stone, who has been at the helm of the Voyagers since the start of the program in 1972:
“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.”
The AGU, to its credit, responded within minutes, reissuing the same press release with details of the findings unchanged, but with a more cautious headline: “CORRECTED — Voyager 1 has entered a new region of space, sudden changes in cosmic rays indicate” [emphasis added]. So, good for the AGU: it conducted a solid study, got called for a little too much breathlessness and stepped back. “It’s a matter of interpretation,” says Peter Weiss, AGU public-information manager. “We were trying to write it in a way that people would understand, so maybe we did get a little overzealous in our headline writing.”
(MORE: Voyager 1 at the Threshold of Forever)
That led to the usual schadenfreude in certain circles, the look-who-screwed-up snickering that always comes when a lab or a government or a politician has to walk back a statement. But the fact is, in this case, nobody misspoke, nobody got it wrong. Weiss is right when he says these things are a matter of interpretation — and that’s one of the reasons they’re so bloody much fun.
This isn’t the first time we’ve tried to determine if or when one of our little machines left the solar system. TIME said we did it in 1983, and before you direct those snickers our way, the scientific community was in complete accord on the matter. That time the spacecraft was Pioneer 10, and what it had done to achieve the landmark feat was cross the orbit of Neptune. Since the elliptical orbit of Pluto (which was a planet then but is no more) at that point took it inside the orbit of Neptune, Pioneer 10 had indeed passed the last recognized toll booth to the unknown.
But here’s the thing: at the time, Pioneer 10 was just 2.8 billion miles (4.5 billion km) away, and Voyager 1 — now 11 billion miles (18 billion km) distant — has nearly quadrupled that stretch. What changed is our subjective definition of where the exit door lies.
(MORE: A Leisurely Cruise on the Good Ship Solar System)
No longer do we define the solar system the way we define the highways around Beijing — with inner, middle and outer rings, all firmly circumscribed. In the same way the sprawl and the smog of Beijing reach far outside the city limits, so too does the solar system make its presence felt beyond the orbit of its last big world, thanks to the heliosphere, a vast gale of charged particles streaming forth from the sun and extending perhaps 12 billion miles (19 billion km) in all directions. Only when the solar wind becomes so attenuated that the outward flowing particles bump up against the higher energy particles of interstellar space do we now consider the solar system at an end. When you change how you draw the map, you entirely upend the sense of where — and even then there is some confusion.
In the summer of 2012, the solar wind surrounding Voyager 1 came to a dead stop, a boundary known as the heliopause, and by some definitions that should have been it, the ship should have been out. And then, capriciously, it just started up again. NASA and the AGU agree that the end game will truly be upon us when the wind stops for good and Voyager punches through the so-called heliosheath, when outward-flowing energy drops to effectively zero and inward-flowing interstellar energy spikes. Those findings were confirmed by the study the AGU released yesterday, leading to the somewhat premature announcement.
But NASA adds another condition — one that the AGU accepts: the magnetic field that surrounds the ship will have to change direction, indicating that solar magnetism is yielding to the deeper magnetism of space. Last December, the fields began interlocking and lining up — putting Voyager on what Stone calls the magnetic highway. But the ship hasn’t taken the exit ramp to deeper space yet. “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,” he said in the NASA release.
Before long, on the order perhaps of months, that will happen — the scientific interpretations will line up as neatly as the magnetic fields and everyone will agree that yes, Voyager 1, first a thing of the earth, then a thing of the local solar system, has well and truly become a thing of the stars. For now, let’s abide — and even enjoy — the uncertainty. On some journeys, the best answer to the question “Where are we?” is a simple “Beats the hell out of me.”
PHOTOS: 11 Billion Miles Later, Photos From the Depths of the Solar System