Jacques Laskar (born 28 April 1955 in Paris) is a French astronomer. He is a research director at the French National Centre for Scientific Research (CNRS), and a member of Astronomy and dynamical systems of the Institute of Celestial Mechanics and Computing Ephemerides (IMCCE) of the Paris Observatory. He received the CNRS Silver medal in 1994. Since 2003, he is a member of the French Academy of Sciences.
After graduation, Laskar taught high school and colleges from 1977 to 1980 at the École Normale Supérieure de Cachan. Then, he taught aggregation mathematics in 1981 and a year later, he taught astronomy and celestial mechanics. He then joined Bureau des Longitudes as a research officer second class of CNRS in 1985.
Stability of the Solar System
In 1989, Laskar provided evidence that the Solar System is chaotic instead of quasi-periodic as originally determined by Laplace and Lagrange. More specifically, his estimate of the maximum Lyapunov exponent measuring the exponential divergence of two nearby orbits is , meaning that it is possible to predict the trajectories of the Solar System over 10 Myr but fundamentally impossible over more than 100 Myr. This chaoticity comes mainly from the inner planets Mercury, Venus the Earth and Mars.
In 2009, he and his colleague Mickaël Gastineau generated numeric simulations of orbital instability over the next five billion years. Unlike previous models, they took into account Albert Einstein's theory of general relativity. Over a short time span, this made little difference, but over the long haul it resulted in dramatically different orbital paths. The researchers looked at 2501 possible scenarios, 25 of which ended with a severely disrupted solar system.
Chaotic obliquity of the planets
Laskar also contributed to the study of the evolution of the skew planets of the solar system. One can for example include his work on retrograde rotation of Venus. With his colleague Alexandre Correia, at Astronomie et Systemes Dynamiques of Paris, he found out that the atmosphere may simply have slowed the planet down and then started it spinning the other way. This insidious process would have been the unique result of the thick atmosphere always lagging behind as the planet rotates.
He has contributed to the astronomical theory of paleoclimates, studying the orbits of the planets and the obliquity of the solar system allowing it to link with the study of climate on geological time scales 
- Member bio at French Academy of Sciences
- Laskar, Jacques (1989). "A numerical experiment on the chaotic behaviour of the Solar System". Nature 338: 237–238. Bibcode:1989Natur.338..237L. doi:10.1038/338237a0.
- Astronomical study of paleoclimate Earth and Mars
- Jacques Laskar's home page on the site of the IMCCE