Audouin Charles Dollfus (12 November 1924 – 1 October 2010[1][2]) was a French astronomer and aeronaut, specialist in studies of the Solar System and discoverer of Janus, a moon of Saturn.

Most of his work was carried out based on observations from the Pic du Midi Observatory, and his preferred research method is the use of polarized light as a diagnostic of the properties of Solar System objects.

He found that only pulverized limonite (FeO(OH)) corresponded with the appearance of Mars, and concluded that the Martian surface could be composed of iron oxide.

Astronomer Gerard P. Kuiper of the University of Chicago disagreed with this conclusion, believing that fine-grained igneous rocks were a better fit to the data, but subsequent observations proved Dollfus correct.

Dollfus announced that he had detected a very small atmosphere, again using polarization measurements made at the Pic du Midi Observatory in the French Pyrenees.

By 1965 Robert S. Richardson called Dollfus one of two great living experienced visual observers as talented as Percival Lowell or Giovanni Schiaparelli.

At this time he probably also observed Epimetheus, a smaller moon which shares the same orbit as Janus, but he did not realize these were two separate objects and it is Richard Walker that holds credit for this discovery.