Has Voyager 1 left the solar system? It depends on who you ask. If you ask NASA, the space agency will say that Voyager 1 “has not yet left the solar system or reached interstellar space.” However, if you ask researcher Marc Swisdak and plasma physicists James F. Drake and Merav Opher, they will say that Voyager 1 left the solar system last summer.
“It’s a somewhat controversial view, but we think Voyager has finally left the solar system, and is truly beginning its travels through the Milky Way,” says Swisdak, a lead author of the study and a University of Maryland research scientist.
Swisdak and his colleagues have created a model of the outer edge of the solar system that concurs with recent observations. Their model reveals that Voyager 1 actually passed into interstellar space last summer, a result directly opposing recent papers by NASA indicating that the probe was still in the heliopause transition zone.
Last summer, NASA reported that Voyager 1 recorded “multiple crossing of a boundary unlike anything previously observed.” According to the space agency, the probe recorded consecutive dips in, and later recovery of, solar particle counts. The dips in solar particle counts were consistent with abrupt increases in galactic electrons and protons. Within a month, solar particle counts ceased, and only galactic particle counts endured. However, the probe detected no change in the direction of the magnetic field.
Many scientists believe that Voyager 1 has passed into a “heliosheath depletion region,” but that the probe is still within the boundaries of the heliosphere.
Swisdak and colleagues think there is an entirely different explanation for the probe’s observations.
According to the researchers, magnetic reconnection is essential to grasping NASA’s data. They contend that the heliosphere is both porous to certain particles and layered with intricate magnetic structure. Magnetic reconnection creates an intricate set of nest magnetic “islands.” Interstellar plasma can access the heliosphere along reconnected field lines, and galactic cosmic rays and solar particles mix furiously.
The researchers point out that drops in solar particle counts and swells in galactic particle counts can take place across “slopes” in the magnetic field, while the magnetic field direction itself remains unaltered. Thus, Swisdak and his colleagues argue that Voyager 1 actually traversed the heliopause on July 27, 2012.
Of course, their model is not the only model trying to interpret NASA’s unusual data.
“Other models envision the interstellar magnetic field draped around our solar bubble and predict that the direction of the interstellar magnetic field is different from the solar magnetic field inside,” says Ed Stone, Voyager project scientist. “By that interpretation, Voyager 1 would still be inside our solar bubble.”
Despite NASA’s disagreement with the study’s findings, the space agency acknowledges the importance of taking these results seriously.
“The fine-scale magnetic connection model will become part of the discussion among scientists as they try to reconcile what may be happening on a fine scale with what happens on a larger scale,” says Stone.
The results are discussed in greater detail in The Astrophysical Journal Letters.