Jacques Laskar (born 28 April 1955 in

Paris Paris () is the capital and most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), making it the 30th most densely populated city in the world in 2020. Si ...

) is a French

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

. He is a research director at the

French National Centre for Scientific Research The French National Centre for Scientific Research (french: link=no, Centre national de la recherche scientifique, CNRS) is the French state research organisation and is the largest fundamental science agency in Europe. In 2016, it employed 31,63 ...

(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 (french: Observatoire de Paris ), a research institution of the Paris Sciences et Lettres University, is the foremost astronomical observatory of France, and one of the largest astronomical centers in the world. Its histo ...

. 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 The French National Centre for Scientific Research (french: link=no, Centre national de la recherch ...

in 1994 and the

Milutin Milankovic Medal The Milutin Milankovic Medal is an annual award in Earth science presented by the European Geosciences Union (EGU). The award was introduced in 1993 by the European Geophysical Society (EGS). After a merger with the European Union of Geosciences ...

in 2019. Since 2003, he is a member of the

French Academy of Sciences The French Academy of Sciences (French: ''Académie des 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 research. It was at ...

Education and early teaching career

After attending the École Normale Supérieure de Cachan, 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 Bureau ( ) may refer to: Agencies and organizations * Government agency *Public administration * News bureau, an office for gathering or distributing news, generally for a given geographical location * Bureau (European Parliament), the administ ...

in 1985.

Research work

Stability of the Solar System

In 1989, Laskar provided evidence that the Solar System is

chaotic Chaotic was originally a Danish trading card game. It expanded to an online game in America which then became a television program based on the game. The program was able to be seen on 4Kids TV (Fox affiliates, nationwide), Jetix, The CW4Kid ...

instead of quasi-periodic as originally determined by

Laplace Pierre-Simon, marquis de Laplace (; ; 23 March 1749 – 5 March 1827) was a French scholar and polymath whose work was important to the development of engineering, mathematics, statistics, physics, astronomy, and philosophy. He summarized ...

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 sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...

, the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...

, and

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

. 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