Physical Sciences: Search for a Trans-Plutonian Planet

Brady and Carpenter1, when working out an ephemeris for the 1986 apparition of Halley's Comet, found they had to include a secular term to explain the observations of previous apparitions. Kiang2 has examined the original records of the apparitions of the comet, and his revised dates of perihelion passage considerably decrease the residuals of Brady and Carpenter's adopted orbit, which includes the secular term. From this term, Brady3 inferred the existence and predicted the position of a trans-Plutonian planet.