News & AnalysisSolar System Dynamics

Mystery Pioneer Anomaly Is Real But Still a Mystery

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Science  02 Sep 2011:
Vol. 333, Issue 6047, pp. 1208
DOI: 10.1126/science.333.6047.1208

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The two Pioneer spacecraft have left the solar system, but something seems not to want them to leave. For years, they seemed to be slowing ever so slightly more than they should as they headed out of the solar system, as if some unknown force were gently tugging them back. Researchers have now unearthed long-forgotten Pioneer records that confirm the reality of this "Pioneer anomaly" and reveal for the first time that the anomaly has actually been shrinking.