This undated file artist's rendering shows one of NASA's twin Voyager spacecraft. NASA says the long-running Voyager 1 spacecraft hurtling toward the edge of the solar system has reached another milestone. Since 2004, the unmanned probe has been exploring a region of space where the solar wind slows abruptly and crashes into the thin gas between stars. NASA said Monday that recent readings show the solar wind has slowed to zero, meaning the spacecraft is getting ever closer to the solar system's edge. (AP Photo/NASA, File)
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