What is the explanation of the Pioneer anomaly?
The Pioneer 10 and Pioneer 11 spacecraft are leaving the the Solar System. Pioneer 10 sent back radio information about its location until January 2003, when it was about 80 times farther from the Sun than the Earth is. Pioneer 11 sent back signals until September 1995, when its distance from the Sun was about 45 times the Earth’s. The Pioneer missions have yielded the most precise information we have about navigation in deep space. However, analysis of their radio tracking data indicates a small unexplained acceleration towards the Sun! The magnitude of this acceleration is roughly 10-9 meters per second per second. This is known as the “Pioneer anomaly”. This anomaly has also been seen in the Ulysses spacecraft, and possibly also in the Galileo spacecraft, though the data is much more noisy, since these were Jupiter probes, hence much closer to the Sun, where there is a lot more pressure from solar radiation. The Viking mission to Mars did not detect the Pioneer anomaly — and it wou
