On April 28, 1905,[1][2]William H. Pickering, who had discovered theSaturnian moonPhoebe seven years earlier, announced the discovery of a tenth Saturniansatellite, which he promptly namedThemis after theGreek goddess of divine law and order. The thirteen photographic plates on which it supposedly appeared spanned a period between April 17 and July 8, 1904. No other astronomer ever confirmed Pickering's claim.
Pickering attempted to compute an orbit, which showed a fairly highinclination (39.1° to theecliptic), fairly largeeccentricity (0.23) and asemi-major axis (1,457,000 kilometres (905,000 mi)) slightly less than that ofHyperion. The period was supposedly 20.85 days, withprograde motion.
Pickering estimated Themis's diameter at 38 miles[2]: 176 (61 km), based on his assumptions that Themis'salbedo was the same asTitan's, and that Titan's diameter was about 2300 miles.[2] (3701.4912 km) Today, Titan's diameter is known to be closer to 3200 miles.[3] (5149.9 km) The same assumptions led him to a diameter of 42 miles[2]: 176 (68 km) for Phoebe, far less than Phoebe's true diameter of roughly 132 miles[4] (213 km).
In April 1861,Hermann Goldschmidt had also believed that he had discovered a new satellite of Saturn between Titan and Hyperion, which he calledChiron. It does not exist, though the name was used much later for the largecomet andcentaur2060 Chiron.
Pickering was awarded theLalande Prize of theFrench Academy of Sciences in 1906 for his "discovery of the ninth and tenth satellites of Saturn".
The actual tenth satellite of Saturn (in order of discovery) wasJanus, which was discovered in 1966 and confirmed in 1980.[6]
Philip Latham (pen-name ofRobert S. Richardson), in his 1953 novelMissing Men of Saturn, has Themis collide with Titan, "getting rid of the little nuisance once and for all", according to the introduction.
John Varley's 1979science fiction novelTitan is set aboard an expedition to Saturn. During the novel, as they approach the planet and prepare to enter orbit, the astronomer onboard discovers a new moon. At first she believes she has recovered Pickering's lost moon, so she names it Themis.
Robert Anton Wilson's 1979-1981Schrödinger's Cat trilogy of novels makes frequent reference to Pickering's Moon as a satellite that revolves the "wrong way" (i. e.retrograde) around its primary. Likewise, thePrincipia Discordia asks in the novel: "Why does Pickering's Moon go about in reverse orbit?"[7]
Nelson S. Bond, in his 1943 science-fiction story "The Ordeal of Lancelot Biggs," explains that Themis periodically disappears when it is occulted by its own moon, an invisible body with "the peculiar property of being able to warp light waves around itself".