Jacques Laskar is a planetary dynamicist who started his scientific career
relatively late, working in classical celestial mechanics at the Bureau
des Longitudes in Paris. In 1988, he had a fundamental breakthrough
when, rather than trying to solve analytically the full equations of
planetary motion (which gives a solution valid only over a short timescale),
he used analytic series manipulations to obtain the planets' secular
equations of motion by averaging over the mean longitude terms and
then integrating the secular equations numerically. This allowed him
to study the evolution of the solar system over 10 to 100 million year
timescales, and to demonstrate that the motion of the terrestrial planets
is chaotic. His secular solution compared successfully with full direct
simulations performed by others. Laskar's work has thus been fundamental
in helping to reveal the chaotic nature of the solar system. In the course
of such studies, Laskar developed a new tool based on frequency analysis
to discriminate regular orbits from chaotic ones that is today widely
used for a variety of problems in conservative dynamics. He and his
collaborators have also made important contributions to the study of
planetary spin axis dynamics. They expanded on previous works to show
that the evolution of the Martian spin axis is chaotic and that the
motion of Earth's spin axis would be chaotic without the Moon. Laskar
and his student, Correia, have also demonstrated that the current
retrograde spin of Venus could be obtained from almost any initial
condition when the perturbations of Venus's orbit by the other planets,
and plausible models for its atmospheric tides and core-mantle interactions,
are accounted for.
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