Voyager 1, the unmanned space probe that was set to bust out of the solar system back in March, has progressed even closer to the edge.
It would be the first human-made object to pierce the heliosphere, a bubble of magnetized particles that surrounds the sun and encapsulates all eight planets, plus Pluto. Papers published in the journal Science on June 27 detail Voyager’s passage from a region containing high amounts of charged particles from inside that bubble to another containing “the highest rate so far of charged particles from outside the heliosphere,” NASA announced.
Voyager’s latest frontier has been dubbed the magnetic highway, NASA said.
"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 in Pasadena, in NASA’s statement. "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."
This does not mean that Voyager’s entry into interstellar space is imminent by human standards, NASA noted. It could take several months, possibly even years, to break free of the solar system’s bubble. Once you get past the planets, there are still 8 billion miles of heliosphere to traverse, a region “dominated by the sun's magnetic field and an ionized wind expanding outward from the sun,” NASA said. “Outside the heliosphere, interstellar space is filled with matter from other stars and the magnetic field present in the nearby region of the Milky Way.”
Voyager 1 was 11 billion miles from the sun when it arrived at the magnetic highway on August 25, 2012. Close behind it, at least by cosmic standards, is Voyager 2, which is 9 billion miles from the sun and solidly inside the heliosphere. The magnetic highway “allows charged particles to travel into and out of the heliosphere along a smooth magnetic field line, instead of bouncing around in all directions as if trapped on local roads,” NASA explained. “For the first time in this region, scientists could detect low-energy cosmic rays that originate from dying stars.”
Scientists have been more cautious this time in making the announcement about Voyager 1’s progress, in contrast to March’s exuberant press release from the American Geophysical Union, which sent out a news release on Wednesday March 20 stating, “Voyager 1 has left the solar system.”
NASA quickly stepped in explaining that although the cosmic particle content had changed, the probe was still solidly within the heliosphere, The New York Times reported.
This week, “scientists reported that, no, Voyager 1 still had not reached interstellar space, but it had entered a region that no one expected and no one can yet explain,” The New York Times said, “a curious zone that is almost certainly the last layer of our Sun’s empire—technically speaking, the heliosphere.”