Voyager 1 at the Threshold of Forever
A 35-year old spacecraft prepares to exit the solar system and enter interstellar space By Jeffrey Kluger Dec. 05, 20120 Share
SSPL / Getty ImagesVoyager 1, launched on 5th September 1977.
Ed Stone has held a lot of jobs in the past 40 years, both at the Jet Propulsion Laboratory (JPL) and Caltech, but there's one he's not giving up: project scientist for the Voyager 1 and 2 space probes. Stone was named to the post in 1972, five years before the Voyagers even left Earth, and in the decades since, he's seen his space babies reconnoiter Jupiter, Saturn, Uranus and Neptune, and then fly on and on through the solar system - on track, eventually, to be the first human-made machines to enter interstellar space. At a news conference on Monday, JPL officials revealed that one of the ships - Voyager 1 - is tantalizingly close to that goal, and Stone was on hand for the announcement.
(Photos: Voyager, 11 Billion Years Later)
Voyager 1, which flew on the flat past Jupiter and Saturn and then swung up and above the plane of the solar system in 1981, is now about 11 billion miles (18 billion km) from home. Voyager 2, which never made such a due north turn and thus flew past all four gas giants, is 9 billion miles (15 billion km distant). It was Voyager 1 that was thus the focus of Monday's report, mostly because of what its few still-functioning instruments are telling it about the magnetic field through which its traveling.
The solar system exists within what's known as the heliosphere - a vast bubble of charged particles given off by the sun. That high-energy gale grows weaker and weaker as it moves away from the center of the solar system, slowing from supersonic speed to what's effectively a standstill as the solar particles bump up against the outside particles of the interstellar medium. The point at which they begin to slow is known as the termination shock, which Voyager 1 crossed in 2004. That took it into the final zone of the solar system - the heliosheath - where solar wind particles swirl about chaotically. No one knows how thick the heliosheath is, but only when Voyager 1 emerges on the other side will it have have truly sailed out among the stars.
(More: Infinity and Beyond)
"We believe this is the last leg of our journey to interstellar space," said Stone at Monday's press conference. "Our best guess is that it's likely just a few months to a couple of years away."
That best guess got better, however, thanks to Voyager 1's new magnetism reports. Even as the particles around the spacecraft continue their random dance, the magnetic field within the heliosphere is now coupling to the magnetic field outside, allowing low-energy charged particles from the solar system to exit and high-energy ones from outside to enter. The actual alignment of the sun's magnetic field has not changed  -  yet  -  but the way it plugs into the larger universe has.
"Although Voyager 1 is still inside the sun's environment," said Stone, "we can now taste what it's like on the outside because the particles are zipping in and out on this magnetic highway. The new region isn't what we expected, but we've come to expect the unexpected from Voyager."
(More: After 34 Years in Space, the Voyager Spacecraft Fly On  -  and On and On)
One more unknown is just what the environment surrounding the ship will look like when it does punch through the film of the heliosheath, but that's becoming clearer too. For about a month in July and August, the solar wind came to a dead stop - the threshold known as the heliopause. That should have been it, the boundary should have been crossed. But the edge of the solar system is apparently a ragged thing, and the wind stirred and fell silent a few times before resuming its motion. "If we were judging by the charged particle data alone, I would have thought we were outside the heliosphere," said Stamatios Krimigis, a Voyager principal investigator. But they weren't judging by the charged particles alone; the ship remained on the newly discovered magnetic highway - still driving along the sun's field lines, albeit ones that are beginning to merge with deeper, more distant ones.
When the first, and then the second of Stone's Voyagers do sail into the interstellar region for good, he will still be able to remain in touch with them. The spacecrafts' radiothermal generators  -  essentially on-board nuclear power plants  -  left Earth with a warranty good for 50 years. That means Voyagers 1 and 2 could still be sending back data in 2027, before finally going cold and dark and continuing their eons-long journey well and truly alone.
Photos: Window on Infinity: Pictures from Space
From the Magazine: Visit to a Large Planet
Jeffrey Kluger
Jeffrey Kluger, senior editor, oversees TIME's science and technology reporting. Kluger's latest book is The Sibling Effect: What the Bonds Among Brothers and Sisters Reveal About Us.
mdillinger2010 5pts
A very well written article to describe this epic journey of human exploration. It is an honor to be a part of this history that will define the next era of mankind.
nvkroeze 5pts
Note: the info after the "Photos" link reads "11 Billion Years Later"...so you may wish to correct that to "11 Billion Miles Later."--Nick
greg.degiere 5pts
The Voyager's reports back to earth from the edge of interstellar space are the most awe-inspiring scientific achievement I can imagine, and it has only traveled 11 billion miles (17 light hours).Think about how much we could learn about the universe from a Voyager 3 and 4 with better scientific instruments designed to travel faster and last longer. And imagine new Voyagers aimed precisely at the nearest star, two light years away, with solar panels to reactivate them when they reach it so they can send first-hand reports back to our descendants of the distant future.How much real, exciting space exploration like the Voyagers and the Mars Curiosity rover could we accomplish for the amount of money we are wasting and planning to waste on human flight to Mars?
CJB 5pts
@greg.degiere I believe the newest star is more like 4 light years away. Proxima Centuari at 4.24 LY.
supamonkey77 5pts
I do hope we make an effort to catch them again for future generations. "Look! Look at that rickety, punctured , bucket of bolts. That's what our forefathers used to first explore interstellar space and dream of distant stars. rwnath 5pts
Brings tears to my eyes.
anarmsxprt 5pts
This will cause a series of catastrophic events.It will put a whole in he heliosphere that will disrupt the balance of the universe and cause the earth to change it's axis.orIt will make contact with hostile aliens that will track back to earth and take our planet as slaves.Either way we are screwed.
TheDisclosure 5pts
@anarmsxprt The ET's aren't hostile.
There are reports that the 'magnetic highway' proves there is an electric universe, thus supporting the theories of Nikola Tesla. This information needs to keep up the pace. This is just the beginning.
GaryRMcCray 5pts
Radiothermal (or SNAP) generators operate based on the half life of the radioactive substance they are composed of, so even after 50 years they won't suddenly shut down but just operate at continually reducing power levels for the next several hundred years.Assuming a properly made power regulation system, that means Voyager could continue to broadcast at reducing intervals for a long time after 2027.