Themis (hypothetical moon)

Themis was a hypothetical moon of Saturn that was claimed to have been discovered in 1905 by American astronomer William Henry Pickering. Pickering believed he had identified the tenth moon of Saturn based on photographic plates taken in April and May 1905 at the Arequipa Observatory in Peru.

Pickering calculated an orbital distance of 1,457,000 km from Saturn, placing it between the orbits of Hyperion and Titan. He estimated a period of 21 days. Themis was assigned a size of approximately 61 km in diameter.

Despite Pickering's announcement and subsequent advocacy, no other astronomer was able to confirm the existence of Themis. The predicted location of the moon, based on Pickering's orbital elements, has been repeatedly searched for, but without success. The photographic plates themselves have been examined and re-examined, yielding no verification.

By 1966, the purported discovery was widely considered erroneous. The lack of independent confirmation and the failure to relocate the object led to the consensus that Themis did not exist. Explanations for Pickering's observations include instrumental flaws, plate defects, or the misidentification of a faint star or asteroid.

The name "Themis" was later adopted for the asteroid 24 Themis, which was discovered in 1853, long before Pickering's claim. The International Astronomical Union (IAU) never officially recognized Pickering's Themis as a satellite of Saturn. Therefore, Saturn does not have a moon officially named Themis. The name is still commonly associated with this historical astronomical error.