Voyager on the voyage outside the universe, time to reach there not predictable

Voyager I , as shown by an artist

Voyager 1 was launched in September of 1977 – and now nearly 36 years later, it’s on the cusp of being the first human-made object to ever leave our solar system. Scientists at NASA believe it’s currently in the last region of the solar system before entering interstellar space. The boundary line (well, less a line than a fuzzily defined region) is the edge of where charged particles carried by solar wind travel to.“This strange, last region before interstellar space is coming into focus, thanks to Voyager 1, humankind’s most distant scout,” NASA researcher Ed Stone said in a press release.Voyager 1 entered that last region, which NASA has referred to as a “magnetic highway,” in August of last year. In this part of space, the Sun’s magnetic field is intersecting with magnetic fields originating in interstellar space. This causes charged particles from the Sun to speed up and head out of our solar system, while charged particles from interstellar space speed up to zoom into our solar system. Some of what NASA has learned about the region so far has been published in this week’s edition of Science. It’s not clear yet when Voyager 1 will leave the solar system – scientists won’t know for sure until it actually gets there. That could be anywhere from a few months to a few years away. It’s sister craft, Voyager 2, is also expected to enter interstellar space, but that will be some time later. Both probes have enough power to last to 2020, so we should learn quite a bit about interstellar space before they fall silent. If either probe happens to meet any extraterrestrial intelligences while it’s out there, though, it won’t matter if they have power or not. Each probe is equipped with a gold record containing images, sounds and other information about us and the Earth. The contents of the records were selected by a committee led by the late scientist Carl Sagan. It contains music from different time periods and cultures, sounds from the Earth like the wind and surf, and 116 different images. It’s pretty unlikely that anyone will actually find either of the Voyager probes to play the record. But to Carl Sagan, that was part of the magic of the two records.“The launching of this ‘bottle’ into the cosmic ‘ocean’ says something very hopeful about life on this planet,” he said at the time.Back in December, NASA announced that the Voyager 1 probe had entered a new region at the edge of our solar system. The region was described as a “magnetic highway,” where charged particles can pass into and out of interstellar space. Since that time, researchers have been anxiously awaiting data that confirms Voyager 1 has become the first man-made object to make it out of the solar system. This week, NASA released an update on Voyager 1′s situation. At 11 billion miles from the sun, the probe is still travelling through the magnetic highway on its way to interstellar space. In the meantime, new research has shed more light on the nature of the magnetic highway, also known as the depletion region.“This strange, last region before interstellar space is coming into focus, thanks to Voyager 1, humankind’s most distant scout,” said Ed Stone, Voyager project scientist at the California Institute of Technology. “If you looked at the cosmic ray and energetic particle data in isolation, you might think Voyager had reached interstellar space, but the team feels Voyager 1 has not yet gotten there because we are still within the domain of the sun’s magnetic field.”NASA researchers are still not sure how long it may take for Voyager 1 to hit the edge of the solar system, saying it could even take years before the probe makes it out of the sun’s magnetic field. The two Voyager probes were launched in 1977 and successfully studied the solar system’s four gas giants before striking out for interstellar space. Voyager 2 is only around 9 billion miles from the sun, and has not yet reached the magnetic highway. Researchers describe the depletion region as a region of space where charged particles stream into and out of the heliosphere along magnetic field lines. Since passing into the region, Voyager 1 can now also detect cosmic rays that originate from stars other than the sun. These two measurements indicate Voyager 1 has exited the solar system, but the direction of the magnetic field measured by the probe has not changed significantly, leading researchers to believe the probe is still within the sun’s magnetic field.“We saw a dramatic and rapid disappearance of the solar-originating particles,” said Stamatios Krimigis, a principal investigator for Voyager’s low-energy charged particle instrument at the Johns Hopkins University Applied Physics Laboratory. “They decreased in intensity by more than 1,000 times, as if there was a huge vacuum pump at the entrance ramp onto the magnetic highway. We have never witnessed such a decrease before, except when Voyager 1 exited the giant magnetosphere of Jupiter, some 34 years ago It's hard to imagine there's another layer between the one we're in and the outside. "Topologically, it makes sense that this is the outermost layer. The only question is: how thick is it?"Launched way back in 1977, the probe has now travelled so far from home that its constant chatter of data takes 17 hours to arrive at the US space agency's receiving network. And chatter, it does. Voyager's instruments are busy sampling the far-flung environment. This has allowed Dr Stone and colleagues to map the shape and reach of the heliosphere - the giant bubble of charged particles blown off from our Sun. In 2004, it reached a turbulent region referred to as the heliosheath, where particles bounced around in all directions.It was expected this would be the final stage before the leap to interstellar space. But, as has been the case throughout this 35-year mission, Voyager threw up yet another surprise. Last year, it detected what appears to be a discrete boundary layer that Ed Stone's team call the "heliosheath depletion region.It is a kind of magnetic highway where energetic particles on the inside can get out easily, and the galactic cosmic ray particles on the outside can zoom in."It is where the Sun's magnetic field has piled up, compressed up against itself. It has also doubled in strength. It's smoother than anything we've ever seen with Voyager," Dr Stone explained.The team is now watching the direction of the field lines very carefully. Currently, they orientate east-west, wound into a spiral by the rotating Sun. But when Voyager finally breaks through into interstellar space, they are expected to shift dramatically, running north-south.This is an acid test for Dr Stone. Although some might argue the particle data is evidence of Voyager being outside the Solar System, the project leader believes the probe cannot truly be said to be beyond the Sun's domain until it has also escaped our star's magnetic influence. But do not expect an immediate, definitive announcement from Nasa that Voyager is in interstellar space when the magnetic signal does switch. Instead, the instrument scientists will sit and listen to the probe's chatter, perhaps for several months. They will want to be absolutely sure Voyager has broken through the so-called heliopause. Like the surfer who rides the front of a breaking wave, battling the foam, Voyager will take some time to move completely clear of everything behind. "This is exploration after all, and we will find out how Nature makes this interface. But it will be moving because the Sun does 'breathe' in and out."Voyager 1 is on course to approach a star called AC +793888, but it will only get to within two light-years of it and take some 40,000 years to make the passage. Voyager 2, which was launched a few weeks before Voyager 1, is on a slightly slower path to interstellar space and is probably a few years from seeing the heliosheath depletion region. Both probes have sufficient power in their plutonium "batteries" to keep working into the next decade.