When NASA’s Voyager 1 became the first spacecraft to enter interstellar space back in 2012, it observed a magnetic field that was inconsistent with models created from observations by other probes, and now researchers believe that they’ve finally discovered why.
Nathan Schwadron, an astrophysicist with the University of New Hampshire Institute for the Study of Earth, Oceans, and Space, and his colleagues reported in Astrophysical Journal Letters that they have resolved inconsistencies in the data sent back by Voyager 1 after it ended its 35-year voyage by punching through the heliosphere.
“There are still naysayers out there regarding Voyager 1 crossing through the heliopause–the edge of the heliosphere,” Schwadron said in a statement, “and the reason for this doubt is that when the spacecraft supposedly broke through the heliopause we should have seen some sort of distinctive shift in the magnetic field from one medium to the other.”
Specifically, when Voyager 1 exited the heliopause, (the boundary where the protective bubble created by the sun’s solar wind meets the interstellar medium) observations of the magnetic field direction in local interstellar space were off by an angle of more than 40 degrees versus expected readings, leading some to suggest that Voyager 1 was still embedded in solar wind.
Probe isn’t expected to fully escape the sun’s influence until 2025
However, using four different datasets gathered from other spacecraft, the UNH-led team found that Voyager 1 did in fact cross the heliopause in 2012, but was traveling through a special region of space where magnetic fields were rotated away from true magnetic north.
Schwadron and his colleagues found that the probe measured the magnetic field using cardinal directions provided by the IBEX (Interstellar Boundary Explorer) mission, which in 2009 found an unusual energy “ribbon” and particles believed to be associated with the interstellar magnetic field. Voyager 1 had been using cardinal directions based on this ribbon, they explained, and its center served as the “true magnetic north” for the pristine interstellar magnetic field.
The initial direction of the magnetic field observed by Voyager 1 had been deflected by the heliopause. So while the probe did exit the heliopause, it is now traveling through a “muddied” magnetic field region and is not expected to reach “pristine” interstellar space until at least 2025. In other words, scientists have to wait a decade or more before Voyager 1 travel fully escapes the reach of the sun’s solar winds.
“Our analysis confirms two things for the first time: that the center of the IBEX ribbon is the direction of the interstellar magnetic field and, secondly, that Voyager 1 is now beyond the heliopause,” said Schwadron, who is also the lead scientist for the IBEX Science Operations Center at UNH. “When Voyager 1 crosses that next boundary we will be poised to probe many longstanding mysteries.”
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Feature Image: NASA/JPL-Caltech
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