The Voyager 1 spacecraft is poised to leave the solar system and reach interstellar space. In fact, it may already have.



Voyager 1 launched in 1977. It's now 17 billion kilometers from Earth. And it should be close to the heliopause, where the plasma flowing outward from the sun no longer holds back the interstellar winds.



The heliopause was expected to be a rather sharp boundary between the sun’s domain and interstellar space. But instead the spacecraft now finds itself in an unexpectedly tranquil zone. Voyager 1 no longer has the wind at its back, so to speak—since last year the velocity of the outward-flowing solar wind has been zero. And it has unexpectedly stayed that way for hundreds of millions of kilometers, according to a mission update in the journal Nature. [Stamatios Krimigis et al., Zero Outward Flow Velocity for Plasma in a Heliosheath Transition Layer"]



That could mean that Voyager 1 is drawing close to the heliopause, which just happens to be surrounded by a broad expanse of calm. Or it could mean that Voyager 1 has already crossed the heliopause. Either way, the spacecraft becomes the first object in interstellar space created by intelligent life. That we know about.

—John Matson

[The above text is an exact transcript of this podcast.]

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