The Pioneer anomaly I read that the Pioneer anomaly is a sunward acceleration that is larger than Newtonian gravity predicts. This extra acceleration has been measured at; (8.74 ± 1.33) × 10−10 m/s2 between 10AU and 90AU from the Sun. But because the ‘extra acceleration’ is constant across about 80 AU of space, how can it be gravitational in nature? If it was gravitational surely the value of the ‘extra acceleration’ would fall, the further away the Pioneer was. At some point this ‘extra acceleration’ would swamp the Newtonian component.