HISTORY OF PLANETARY SCIENCE - THE PIC-DU-MIDI PLANETARY OBSERVATION PROJECT - 1941-1971

When, in 1941, Bernard Lyot attempted to observe planet Mars at Pic du Midi, he experienced unusual viewing conditions. He realized that thi s circumstance was not at all exceptional for the Pic but representati ve of a remarkable property of the high altitude site. He decided to d esign, and put into operation at the top of the mountain a refractor, 60 cm in diameter, specially conceived for high angular resolution. Wi th such a capability, Henry Camichel, Jean Focas and Audouin Dollfus i nitiated a deep and long-term research project based upon planetary su rface exploration, with high telescopic magnification. Visual analysis , photographic work, double image micrometry, photometric and polarime tric sensing were the most frequently used techniques and they were co mbined. Full exploitation of all these approaches required 30 years of continuous work, essentially coordinated by Observatoire de Paris at Meudon. The project was completed almost at the time when spacecraft m issions within the Solar System began to replace telescopic work for p lanetary physics. At this time, the Pic du Midi work have released new basic physical properties about planets and satellites.,Knowledge was acquired and fundamental problems settled: which are reviewed. (C) 19 98 Elsevier Science Ltd. All rights reserved.