Unraveling the Mystery of the Pioneer Anomaly: NASA Probes' Fate at 20 Astronomical Units

NASA's Pioneer 10 and 11 probes experienced an anomalous acceleration towards the Sun when they reached around 20 astronomical units (AU) from Earth, challenging Newton's gravitational inverse-square law. Some physicists proposed new physics or the expansion of the universe as possible explanations. However, further analysis of Doppler data revealed that the acceleration was due to the recoil force caused by an anisotropic emission of thermal radiation from the spacecraft. This finding suggests that there was no anomaly and that Newton's inverse-square law remains valid.