Jacques Laskar (born 28 April 1955 in

Paris Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, largest city of France. With an estimated population of 2,048,472 residents in January 2025 in an area of more than , Paris is the List of ci ...

) is a French

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

. He is a research director at the

French National Centre for Scientific Research The French National Centre for Scientific Research (, , CNRS) is the French state research organisation and is the largest fundamental science agency in Europe. In 2016, it employed 31,637 staff, including 11,137 tenured researchers, 13,415 engi ...

(CNRS), and a member of ''Astronomy and dynamical systems'' of the Institute of Celestial Mechanics and Computation of Ephemerides (French: IMCCE) of the

Paris Observatory The Paris Observatory (, ), a research institution of the Paris Sciences et Lettres University, is the foremost astronomical observatory of France, and one of the largest astronomical centres in the world. Its historic building is on the Left Ban ...

. He received the

CNRS Silver Medal The CNRS Silver Medal is a scientific award given every year to about fifteen researchers by the French National Centre for Scientific Research (CNRS). It is awarded to a researcher for "the originality, quality and importance of their work, re ...

in 1994 and the Milutin Milankovic Medal in 2019. Since 2003, he is a member of the

French Academy of Sciences The French Academy of Sciences (, ) is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French Scientific method, scientific research. It was at the forefron ...

Education and early teaching career

After attending the

École Normale Supérieure de Cachan École or Ecole may refer to: * an elementary school in the French educational stages normally followed by secondary education establishments (collège and lycée) * École (river), a tributary of the Seine flowing in région Île-de-France * Éco ...

, Jacques Laskar taught secondary school from 1977 to 1980 and passed the aggregation in mathematics in 1981. He then studied astronomy and celestial mechanics, finishing his thesis in 1984. He became a CNRS researcher at the

Bureau des Longitudes __NOTOC__ The ''Bureau des Longitudes'' () is a French scientific institution, founded by decree of 25 June 1795 and charged with the improvement of nautical navigation, standardisation of time-keeping, geodesy and astronomical observation. Durin ...

in 1985.

Research work

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 Pierre-Simon, Marquis de Laplace (; ; 23 March 1749 – 5 March 1827) was a French polymath, a scholar whose work has been instrumental in the fields of physics, astronomy, mathematics, engineering, statistics, and philosophy. He summariz ...

and

Lagrange Joseph-Louis Lagrange (born Giuseppe Luigi LagrangiaLyapunov exponent In mathematics, the Lyapunov exponent or Lyapunov characteristic exponent of a dynamical system is a quantity that characterizes the rate of separation of infinitesimally close trajectory, trajectories. Quantitatively, two trajectories in phase sp ...

measuring the exponential divergence of two nearby orbits is

1/5 \; \text^

, 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 Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

, the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

, and

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

. In 2009, he and his colleague Mickaël Gastineau generated numerical simulations of orbital instability over the next five billion years. Their model, unlike those used by previous researchers, took into account Albert Einstein's theory of general relativity. This made little difference over a short time span, but resulted in dramatically different orbital paths over long times. 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.

Paleoclimates

He has contributed to the astronomical theory of paleoclimates, studying the orbits of the planets and the obliquity of the solar system and relating it to the study of climate on geological time scales Astronomical study of paleoclimate Earth and Mars
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References

External links

Jacques Laskar's home page
on the site of the IMCCE {{DEFAULTSORT:Laskar, Jacques 20th-century French astronomers Members of the French Academy of Sciences 1955 births Living people Scientists from Paris 21st-century French astronomers Research directors of the French National Centre for Scientific Research