The Pioneer Anomaly

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The Pioneer Anomaly

• Jonas Williamson
• University of St. Thomas,
• St. Paul, MN

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The Pioneer Anomaly

• What Is the Pioneer Anomaly?
• What are some possible explanations?
• Some less probable, but interesting explanations.

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Pioneer 10 and 11

• Pioneer 10
• Was Launched on March 2, 1972.
• Was the first man-made object to travel beyond
  the asteroid belt.
• Obtained the first close-up pictures of Jupiter
• Pioneer 11
• Was Launched on December 4, 1973
• Took the first close-up pictures of Saturn.

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Pioneer 10 and 11

• Were spin-stabilized, requiring a minimum number
  of attitude corrections with thrusters.
• Had Radioisotope Thermoelectric Generators
  (RTG's) on extended booms.
• Made the spacecraft more stable
• Simplified the thermodynamics of the system.
• Were able to be tracked with Doppler Radar.
• All these characteristics made the two craft the
  most precise long-term spaceflight to date.

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The Anomaly

• In 1980, Pioneer 10's heliocentric distance
  exceeded 20 AU.
• Acceleration due to solar radiation (light and
  particles) dropped below .
• At that time, it was noticed that the doppler
  tracking signals were consistently blueshifted by
  an amount that indicated an acceleration of
  toward the sun!

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The Anomaly, continued

• The same acceleration may have been seen in the
  Galileo, Cassini, and Ulysses missions, but their
  proximity to the sun makes it hard to say.
• The effect continues to manifest itself as a
  constant acceleration, even after 25 years and
  over 60 AU of travel
• The Pioneer spacecraft have deviated from their
  intended course by about the distance between the
  Earth and the moon.

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Even Weirder...
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(No Transcript)
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So what's Going on?

• Some of the more likely explanations
• Leakage
• Outgassing
• Solar Pressure
• Kupier Belt density
• Drag from Dust
• EM Forces

• Something Else

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Leakage

• The Radioisotope Thermoelectric Generators could
  be leaking
• Hydrogen or Helium Atoms
• Design unlikely to cause sunward acceleration
  alone (torque).
• Would not account for constant acceleration
• Heat/Blackbody Radiation
• Would not account for constant acceleration
• Would not be strong enough to cause the
  acceleration seen.

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Outgassing
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Solar Pressure

• Less pressure than expected from solar radiation
  (light, solar wind, etc) might explain the
  phenomenon.
• The effect would not be constant, but would
  decrease following an inverse square curve.

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Kupier Belt Density
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Drag

• If space were dustier than expected, this would
  cause a drag that would cause acceleration toward
  the sun.
• Why haven't we noticed it?
• Why would it be constant?

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EM Forces
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Other Ideas
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Other Ideas

• Dark Matter
• New Physics
• Variations in the speed of light?
• Dynamic Time?
• Gravity Leaks?

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Dark Matter
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Speed of Light Variations?

• The expansion of the Universe suggests that the
  observable, or non-proper speed of light could
  be increasing.
• Non-proper light speed depends on the
  gravitational potential, ?, which is decreasing
  as time goes on.
• The frequency shift seen from a guess of a
  background gravitational potential is only off
  by about 40.

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Dynamic Time

• Time could be passing at different rates in
  different places.
• Would be related to variations in the speed of
  light.
• Under the right conditions an acceleration of
  coordinate time with respect to proper time
  would manifest itself as a Doppler blueshift, and
  be misinterpreted as an acceleration.
• Hard to test, if not untestable.

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Strings, Branes, and Gravity Leaks

• Some string theorists think that Gravity can leak
  into other Braneworlds.
• Why shouldn't the opposite happen as well?

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Gravity Leaks
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Problems with Gravity Leaks

• It would seem unlikely that there would be a
  large mass near the position of our sun.
• Why has there been no relative brane-motion over
  25 years?
• Theory is untestable.

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Sources

• Bertolami and Paramos, The Pioneer Anomaly in the
  Context of the Braneworld Scenario, ArXiv
  gr-qc/0310101 (preprint, 4 Jun 2004)
• Diego et al. Pioneer Anomaly? Gravitational Pull
  due to the Kupier Belt, ArXiv Astro-ph/0503368
  (16 Mar 2005)
• Nieto and Turyshev, Finding the Origin of the
  Pioneer Anomaly. ArXiv gr-qc/0308017 (Preprint,
  18 Jun 2004)
• Nieto et al., The Pioneer Anomaly The Data, its
  Meaning, and a Future Test, ArXiv gr-qc/0411077
  (Preprint, 22 Nov 2004)

• Ranada, Pioneer Acceleration and Variation of
  Light Speed Experimental Situation, ArXiv
  gr-qc/0402120 (preprint, 3 Mar 2004)
• Ranada, The Pioneer Anomaly as an Effect of the
  Dynamics of Time, ArXiv gr-qc/0403013 (preprint,
  25 Nov 2004)
• Rosales, Pioneer's Anamolous Doppler Drift as a
  Berry Phase, ArXiv gr-qc/0401014 (preprint, 13
  May 2004)

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