Audouin Dollfus observed a moon on Dec. 15, 1966, for which he proposed the name "Janus." On 18 December of the same year, Richard Walker made a similar observation, now credited as the discovery of Epimetheus. At the time, astronomers believed that there was only one moon, unofficially known as "Janus," in the given orbit. Twelve years later, in October 1978, Stephen M. Larson and John W. Fountain realized that the 1966 observations were best explained by two distinct objects (Janus and Epimetheus) sharing very similar orbits. Voyager I confirmed this in 1980.