Unexplained Mysteries :: NASA baffled by unexplained force

Unexplained Mysteries :: NASA baffled by unexplained force: "user posted image rMysteriously, five spacecraft that flew past the Earth have each displayed unexpected anomalies in their motions. These newfound enigmas join the so-called 'Pioneer anomaly' as hints that unexplained forces may appear to act on spacecraft. A decade ago, after rigorous analyses, anomalies were seen with the identical Pioneer 10 and 11 spacecraft as they hurtled out of the solar system."