Something strange is happening in the outer reaches of our solar system. The Pioneer 10 and 11 spacecraft are not where they are supposed to be. These missions, launched in 1972 and 1973, have covered hundreds of millions of kilometers, heading toward the edge of our solar system. But something is holding them back. Each year, they fall behind in their projected travel by about 5,000 kilometers (3,000 miles).
Jet Propulsion Laboratory scientist John Anderson and his colleagues have been searching for an explanation since 1980. But as of yet, they have found nothing conclusive; no spacecraft behavior or previously unknown property of the outer solar system can explain the deceleration of the Pioneer spacecraft. Scientists are being forced to consider the unthinkable: something may be wrong with our understanding of the laws of physics. An important line of inquiry will be to study mounds of Doppler (velocity) data and spacecraft status data (like temperatures) that have been unavailable to researchers—but that is about to change.
The Planetary Society, using support from its members, is currently sponsoring the recovery of Doppler and spacecraft status data, as well as analysis of that data. NASA was not ready to allocate resources to recover the Pioneer data, or sponsor its analysis. Anderson and his colleague Slava Turyshev, contacted The Planetary Society for help, requesting funds to support the use of the antiquated computers to read out the pre-1987 Pioneer tapes and convert them to a format useable by researchers. And, they sought funding to seek additional sources of Pioneer data, and to support analyses of the data. The Planetary Society sent an appeal to members to help save the data from destruction and then support the complex analyses necessary to solve the mystery. Our members and supporters responded with unprecedented enthusiasm.
The process was started, and is going very well. The data are successfully being recovered and saved. They will be made available for other researchers as well, and analysis will be starting soon. In our updates section, you can learn more. Only about 11 years of data had been analyzed in detail before. We hope to recover data covering nearly 30 years to help solve the mystery, in addition to recovering never before analyzed spacecraft status data that will be valuable in assessing possible spacecraft influences on the anomaly.
Whether it turns out to be an annoying spacecraft effect or a revolution in physics, the Pioneer Anomaly is a mystery that must be solved as we continue to explore the universe around us.