Closing In On The Famous Pioneer Anomaly

"The recovery of Doppler and telemetry data and the entire effort in thermal analysis would not have happened without the Planetary Society," said Turyshev. "The members provided the money we needed to get started and demonstrated to NASA that the public was definitely interested in solving the mystery. Their interest and strong support made possible our work to solve the Pioneer Anomaly."

Scientists working with recovered data from the Pioneer 10 and 11 missions are closing in on a solution to the famous Pioneer Anomaly. Their just-published results show that the mysterious effect on the two spacecraft is not constant over time, probably indicating that no outside force is acting on the Pioneers, but rather, something inside the spacecraft is to blame.

Slava Turyshev and a team of researchers are publishing an upcoming issue of Physical Review Letters their analysis of radio transmission data from the spacecraft. (The article is available on-line.) Their work strengthens the case that the source of the anomaly lies in the spacecraft themselves, not in any mysterious outside force acting on them. The most likely cause is heat generated by spacecraft systems, producing a recoil force.

The Pioneer Anomaly was defined as "anomalous acceleration in the direction of the Sun" or, as seen from Earth, the spacecraft appeared to be slowing down. It was first detected in 1980 by John D. Anderson of the Jet Propulsion Laboratory through his analysis of the Doppler shift in the radio signal from the Pioneers 10 and 11 on their way out of the solar system, after becoming the first spacecraft to fly by Jupiter and Saturn.

Since its discovery, suggested solutions to the Pioneer Anomaly have ranged from such things as the gravity of as-yet undetected bodies in the solar system, dark matter or dark energy, the cosmic expansion, to some sort of New Physics, such as modifications to the theory of gravity. For over 20 years, scientists around the world have been seeking an explanation.