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Has Voyager 1 entered interstellar space? NASA says not yet

Has Voyager 1 left our solar system? That seems to be the question making the rounds at NASA after reports surfaced that the space probe has exited our solar system and entered interstellar space.

The debate seems to stem from a report released by the American Geophysical Union (AGU), which on Wednesday announced that researchers studying the position of the probe had reached a consensus: Voyager 1 has entered interstellar space.

“Within just a few days, the heliospheric intensity of trapped radiation decreased, and the cosmic ray intensity went up as you would expect if it exited the heliosphere,” said lead researcher Bill Webber, professor emeritus of astronomy at New Mexico State University in Las Cruces.

However, according to NASA’s Jet Propulsion Laboratory (JPL) that’s not so. In a statement released through the agency on Wednesday, JPL officials refuted the assertion, saying Voyager 1’s position clearly places it within the boundaries of the solar system, not interstellar space.

“The Voyager team is aware of reports today that NASA’s Voyager 1 has left the solar system,” said Edward Stone, Voyager project scientist at the California Institute of Technology. “It is the consensus of the Voyager science team that Voyager 1 has not yet left the solar system or reached interstellar space. We believe this is the last leg of our journey to interstellar space. Our best guess is it’s likely just a few months to a couple years away. The new region isn’t what we expected, but we’ve come to expect the unexpected from Voyager.”

The Voyager team has repeatedly said Voyager 1’s position places it within the solar system because the direction of the magnetic field lines has not changed. The direction of these magnetic field lines is predicted to change when Voyager breaks through to interstellar space, although data collected by the probe has ignited a debate over exactly when that change is expected to take place.

The debate largely revolves around a small region of space separating the solar system from interstellar space. The heliosphere, the region of space dominated by the Sun and its wind of energetic particles, is thought to be enclosed from the surrounding interstellar medium of gas and dust that pervades the Milky Way galaxy.  Voyager I began to enter a new region between August and December 2012, when data collected by the probe showed a significant decrease in the number of sun-charged particles and radiation.

The debate allows stems from some unusual findings collected by the space probe as it continues its journey through space. NASA noted the probe’s sensors registered drastic changes in radiation levels in August of 2012, the first indication Voyager 1 had entered a new region of space.  In addition, the stream of charged particles from the sun — known as the solar wind — abruptly slowed down from supersonic speeds and became turbulent. The spacecraft then detected that the outward speed of the solar wind slowed to zero.

Through all the changes, however, the magnetic field lines did not change. The result has left NASA scientists scrambling to explain the lack of a change in the direction of the  magnetic field, and some have even suggested that additional data may serve as an impetus to rethink the theory. Still, NASA maintains that until it can prove otherwise, Voyager I remains within the solar system is started out in.

“We are in a magnetic region unlike any we’ve been in before — about ten times more intense than before the termination shock — but the magnetic field data show no indication we’re in interstellar space,” said Leonard Burlaga, a Voyager magnetometer team member based at NASA’s Goddard Space Flight Center in Maryland.

It will take months of additional data analysis before it becomes clear whether the probe has entered interstellar space. Until that time, scientists will likely keep debating and Voyager 1 and 2 will continue their trip through the cosmos.

The study is published in Geophysical Research Letters.