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Pioneer puzzle pinned on thermodynamics

New study declares long-standing mystery solved, but experts are skeptical

A puzzling deceleration of the Pioneer 10 and 11 spacecraft as they drift toward the edge of the solar system is almost certainly due to forces generated by onboard heating elements rather than an exotic force or modification of gravity, a new study concludes. But other researchers say the study, posted April 1 at, doesn’t fully explain the anomalous motion.

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