In December 2012, a group of space scientists gathered in San Francisco to hold a vote. The lone issue on the ballot: Is Voyager 1 in, or is it out?
Throughout that year, the hardy spacecraft had beamed back tantalizing hints that it had left the heliosphere, the magnetic bubble inflated by the solar wind, and become the first human-made object to enter interstellar space. Yet mission scientists weren’t seeing what they had thought would be the unambiguous signature of Voyager’s departure: a sudden shift in direction of the magnetic field. It seemed inconceivable that the probe could have left a river of charged particles flowing from the Sun for an ocean of interstellar plasma without drastic magnetic deviations. “That was truly a shock to all of us,” says Len Burlaga, coinvestigator of the magnetometer instrument. “We figured that in a completely different region [the field direction] wouldn’t be the same.”
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