The Pioneer Anomaly Jonas Williamson University of St. Thomas, St. Paul, MN

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

Pioneer 10 and 11 ● Pioneer 10 – Was Launched on March 2, – 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.

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.

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!

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.

Even Weirder...

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

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.

Outgassing

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.

Kupier Belt Density

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?

EM Forces

Other Ideas

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

Dark Matter

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%.

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.

Strings, Branes, and Gravity Leaks ● Some string theorists think that Gravity can leak into other Braneworlds. ● Why shouldn't the opposite happen as well?

Gravity Leaks

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.

Sources ● Bertolami and Paramos, The Pioneer Anomaly in the Context of the Braneworld Scenario, ArXiv: gr- qc/ (preprint, 4 Jun 2004) ● Diego et al. Pioneer Anomaly? Gravitational Pull due to the Kupier Belt, ArXiv: Astro-ph/ (16 Mar 2005) ● Nieto and Turyshev, Finding the Origin of the Pioneer Anomaly. ArXiv: gr-qc/ (Preprint, 18 Jun 2004) ● Nieto et al., The Pioneer Anomaly: The Data, its Meaning, and a Future Test, ArXiv: gr-qc/ (Preprint, 22 Nov 2004) ● Ranada, Pioneer Acceleration and Variation of Light Speed: Experimental Situation, ArXiv: gr- qc/ (preprint, 3 Mar 2004) ● Ranada, The Pioneer Anomaly as an Effect of the Dynamics of Time, ArXiv: gr-qc/ (preprint, 25 Nov 2004) ● Rosales, Pioneer's Anamolous Doppler Drift as a Berry Phase, ArXiv: gr-qc/ (preprint, 13 May 2004)

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