Did NASA's Voyager I actually leave the solar system?

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For a hot second on Wednesday, it appeared as though NASA's Voyager I—one of two spacecraft launched in '77 to observe the outer planets—had left our solar system.

In a paper accepted by the journal Geophysical Review Letters, William R. Webber of New Mexico State University and Frank B. McDonald of the University of Maryland reported that on Aug. 25 last year, the spacecraft observed a sudden change in the mix of cosmic rays hitting it.

The piece prompted NASA officials to respond with a counter point, positing that Voyager I had not yet reached interstellar space.

“It is the consensus of the Voyager science team that Voyager 1 has not yet left the solar system or reached interstellar space,” Dr. Stone said. He said that the critical indicator would be a change in the direction of the magnetic field, not cosmic rays, for marking the outermost boundary of the solar system.

Later, the geophysical union sent a revised piece with the headline, "Voyager 1 has entered a new region of space." [NYTimes]

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