Dollfus was born in Paris to aeronaut
Charles Dollfus. Dollfus studied at the
University of Paris, obtaining a doctorate in physical sciences in 1955. Beginning in 1946, Dollfus worked as an astronomer at the Meudon Observatory, following his advisor and mentor
Bernard Lyot. In particular, he directed the Laboratory of Solar System Physics there. Until his death, he was an honorary astronomer at the
Paris Observatory. 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. Through patient and persistent research and the development of new observational techniques, he was able to obtain many remarkable results. Dollfus published more than 300 scientific publications, relating primarily to astrophysics of the Solar System. Before the
Viking spacecraft landed on
Mars, the composition of the Martian surface was the subject of many debates. Dollfus tried to determine the composition of the Martian desert, through comparison with the appearance in polarized light of several hundred terrestrial
minerals. 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. By using the polarization of light, it is possible to detect an
atmosphere around a planet or
natural satellite. In 1950, most scientists thought that
Mercury, because of its small size, had probably lost its atmosphere due to molecular escape into space. 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. His discovery contradicted the previous theoretical predictions based on the kinetic theory of gases. Dollfus estimated that the atmospheric pressure at the surface of Mercury was approximately 1 mm of
mercury. The nature of gas composing this atmosphere was unknown but thought to be a dense, heavy gas. It was however certain that the atmosphere of Mercury must be less than 1/300th that of the
Earth. Currently, it is known that the atmosphere of Mercury is very thin indeed: only 10−15
bar, with the total mass of the atmosphere not exceeding 1000 kg. Mercury has dark zones which contrast with a brighter bottom; this was observed first by
Giovanni Schiaparelli in 1889. By using the refracting telescope of the Pic du Midi Observatory, Dollfus was able in 1959 to clearly resolve surface features as small as 300 km. Dollfus also studied the possible presence of an atmosphere around the
Moon. The rate of dissipation into space of any gases on the Moon (except for certain rare heavy elements) is so high that no substantial atmosphere is possible. The presence of any atmosphere should be detectable by the polarization of light; Bernard Lyot and later Dollfus showed that there was no detectable polarization, thereby confirming the theoretical prediction that the Moon lacks an atmosphere. Direct visual observation became rare in astronomy. By 1965
Robert S. Richardson called Dollfus one of two great living experienced visual observers as talented as
Percival Lowell or
Giovanni Schiaparelli. In 1966, Dollfus discovered
Janus, a small inner moon of
Saturn. He made this discovery by observing at a time when the rings, very close to Janus, were nearly edge-on to the Earth and thus practically invisible. 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. In 1981, Dollfus became a founding member of the
World Cultural Council. ==Aerospace and Ballooning Pioneer==