Robert Sutton Harrington (October 21, 1942 – January 23, 1993) was an Americanastronomer who worked at theUnited States Naval Observatory (USNO). Harrington was born nearNewport News,Virginia. His father was anarchaeologist. He was married toBetty-Jean Maycock in 1976, with two daughters, Amy and Ann.[1]
Harrington worked at the USNO. Another astronomer there,James W. Christy, consulted with him after discovering bulges in the images ofPluto, which turned out to be Pluto'ssatelliteCharon.[1] For this reason, some consider Harrington to be a co-discoverer of Charon,[2] although Christy usually gets sole credit. By the laws ofphysics, it is easy to determine themass of a binary system based on its orbital period, so Harrington was the first to calculate the mass of the Pluto-Charon system, which was lower than even the lowest previous estimates of Pluto's mass.
For much of his career, he proposed the existence of aPlanet X beyond Pluto and supported searches for it, collaborating initially withT. C. (Tom) Van Flandern.[1]
Harrington died ofesophageal cancer in 1993.[1] Theasteroid3216 Harrington was named in his honour.
Six months before Harrington's death,E. Myles Standish had used data fromVoyager 2's 1989 flyby ofNeptune, which had revised the planet's total mass downward by 0.5%—an amount comparable to the mass ofMars[3]—to recalculate its gravitational effect onUranus.[4] When Neptune's newly determined mass was used in theJet Propulsion Laboratory Developmental Ephemeris (JPL DE), the supposed discrepancies in the Uranian orbit, and with them the need for a Planet X, vanished.[5] There are no discrepancies in the trajectories of any space probes such asPioneer 10,Pioneer 11,Voyager 1, andVoyager 2 that can be attributed to the gravitational pull of a large undiscovered object in the outer Solar System.[6] Although most astronomers agree that Planet X, as Lowell defined it, does not exist,[7] as of 2025 there is speculation concerningPlanet Nine, a distinct hypothetical planet in the outer Solar System. Although the evidence and orbital properties of Planet Nine are very different from those of Harrington's Planet X, the mass estimates are similar: Planet Nine is approximately 4.4Earth masses[8] while Harrington's Planet X was estimated to be 4 Earth masses.[9]
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