With the latest piece of the puzzle just published in a scientific journal, a solar system mystery that has perplexed people for more than 20 years has been solved, truly thanks to the support of Planetary Society members. That mystery is the “Pioneer Anomaly,” an anomalous acceleration that affected the two Pioneer spacecraft as they left the solar system.
Pioneers 10 and 11 were launched in the early 1970’s. As they traveled away from the Sun, they slowed down. Most of this slowing was expected, a result of the gravitational pull of the Sun and other massive objects in the solar system. But even when everything in the solar system whose mass could have any effect on the Pioneers was accounted for, both spacecraft were found to be slowing more than expected. The excess slowing was very tiny, but measurable.
Over the course of the past two decades, all sorts of solutions have been proposed, some of which invoked exotic “new” physics. In the end, recovery of more data and years of painstaking work have shown that no such exotic solution is necessary, but rather that anisotropic (big word for not-symmetric-in-all-directions) thermal radiation (big words for heat) can explain the mystery. This solution had already been suggested, and examination of the problem over time had made it seem increasingly likely, but only careful analyses could check whether anisitropic radiation could explain the anomaly. The latest piece of this analysis appears in a new scientific article by Slava Turyshev and colleagues.
The only way to solve this mystery was to look at much more data than had previously been available. That is where Planetary Society members stepped in. A few years ago, Slava Turyshev and his colleagues at the Jet Propulsion Laboratory were in desperate need of funding to help them do just that. With funds supplied by our members, Turyshev successfully chased down data from a number of sources. This was not an easy (or quick) task. These missions lasted for more than 30 years. Imagine all the people, computing formats, and hardcopy and electronic storage devices involved over that period, and you’ll start to get an idea of the problem.