KellyYoung writes "The Pioneer 10 and 11 spacecraft gave us some of the earliest close-up pictures of the outer planets. They also gave us a curious puzzle now known as the Pioneer anomaly. http://space.newscientist.com/article/dn11304-com
p uter-sleuths-try-to-crack-pioneer-anomaly.html Even though both spacecraft were heading in different directions, both experienced a tiny deceleration. It was as if the Sun's gravity was pulling a little harder than Newton's laws predicted. Scientists are hoping to know within a year whether the Pioneer anomaly is due to an issue with the two spacecraft themselves, namely the heat generated by their onboard nuclear generators. An international team of scientists are re-analyzing the tracking and telemetry data to look for clues."