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Pioneer Anomaly
Information about the Pioneer Anomaly and anomalous velocity increases during Earth flyby's.
Chris P. Duif
Pioneer 10
Artist impression of Jupiter flyby of Pioneer 10

    The Pioneer Anomaly

    The Pioneer missions yielded the most precise information we have about navigation in deep space. However, analysis of their radio tracking data indicates a small unexplained acceleration towards the Sun! The magnitude of this acceleration is roughly 10-9 m/s2. It is called the "Pioneer anomaly".
    This anomaly has also been seen in the Ulysses spacecraft, and possibly also in the Galileo spacecraft, though the data is much more noisy, since these were Jupiter probes, hence much closer to the Sun, where there is a lot more pressure from solar radiation. The Voyagers are not set up to provide good data on this issue, since they are able to rotate themselves and this messes things up. The Viking mission to Mars did not detect the Pioneer anomaly - and it would have, had an acceleration of this magnitude been present, because its radio tracking was incredibly accurate - good to about 12 meters.
    Many physicists and astronomers have tried to explain the Pioneer anomaly using conventional physics, but so far nobody seems to have succeeded. Radiation pressure from the Sun, the solar wind, the back-reaction from the radio emissions: all these point the wrong way! Other explanations also seem to fail, like gravity from the Kuiper belt, small amounts of gas venting from the spacecraft, and thermal radiation from the crafts.
    As conventional explanations seemed to fail, people started trying to explain the anomaly using new physics - for example, modified theories of gravity, or dark matter. But it's hard to get these explanations to work, either. For example, explaining the Pioneer anomaly by the gravitational attraction of dark matter would require more than 0.0003 solar masses of dark matter within 50 AU units of the Sun. But this is in conflict with our highly successful calculations of planetary orbits - even a millionth of a solar mass of dark matter in this region would be enough to throw those off!     [text from John Baez]

  • New review article by Turyshev and Toth: The Pioneer Anomaly, January 2010, on ArXiv
  • Independent analysis confirms existence of Pioneer Anomaly: V.T. Toth, Jan. 2009.
  • Pioneer Anomalous Acceleration (article by Anderson et al. (2002) at arXiv)
  • ESA: Pioneer anomaly put to the test
  • New Mission Would Probe Strange Puzzle
  • NASA Pioneer homepage.

  • Furthermore, see the literature and Links Page

    News: Computer sleuths try to crack Pioneer anomaly (New Scientist, March 2007)
      Pioneer data tapes

    June 1, 2006: Data Saved!
       Newfound Data Could Solve NASA's Great Gravity Mystery

    Piles of Pioneer data tapes!

2004-2010 RandomLab, The Netherlands Last update:  February 12, 2010