He often tells this anecdote. How, as a young researcher, he was denied a promotion for claiming that the solar system is “chaotic”. “Since the beginning of the nineteenthe century, we know that the planets have regular and stable trajectories., had then replied the jury. Nowadays, such a misadventure would no longer risk happening to Jacques Laskar. The idea according to which it will never be possible to predict, with precision, the long-term movements of the Earth, the Moon and in general of all the celestial bodies is a consensus within the scientific community. And he himself has acquired a solid reputation: member of the Academy of Sciences since 2003, director of research at the CNRS, he has been, for five years, and for a few more weeks, at the head of the prestigious Institute of Celestial Mechanics and ephemerides calculation center (IMCCE) of the Paris-PSL Observatory.
Described by one of his former accomplices, the mathematician and professor emeritus at the University of Paris, Alain Chenciner, as a scientist “remarkable”to the ” strong personality “ and equipped with a “great determination”, Jacques Laskar was not, however, destined to one day become one of the best connoisseurs of the inner workings of the grand horology of the planets. It would even be quite the opposite if we were to stick to his erratic career as a militant student of the 1970s. Cachan, teaches in technical high schools, begins studies of psychology and passes the aggregation of mathematics.
All this before landing, somewhat by chance, at the Paris Observatory where he followed the teachings of a DEA in astronomy and celestial mechanics which continued with a thesis. Chaos was out of the question in 1983 within the Bureau des Longitudes where this doctorate began. The planets obey the laws of gravitation and general relativity defined by Newton and Einstein, but influence each other in their courses around the Sun. “And it was a question of taking advantage of advances in computing, to try to determine with high precision the trajectory followed by the Earth going far back in the past”, says Jacques Laskar. Indeed, a tiny modification of the orbit or the inclination and the precession of the axis of rotation is enough to significantly change the insolation of the terrestrial globe and therefore its climate. “Hence the idea of accessing, through the use of astronomy, information on how the latter had evolved during ancient periods. »
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