Jacques Laskar

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Jacques Laskar (born April 28, 1955 in Paris ) is a French astronomer, known for celestial mechanical investigations that gave evidence of chaotic behavior in the solar system.

Life

Laskar studied mathematics from 1974 to 1977 at the École normal supérieure de Cachan (diploma 1976) and was then a school teacher. In 1981 he received his Aggregation in Mathematics and in 1982 his DEA in Astronomy and Celestial Mechanics at the Paris Observatory, where he received his PhD in 1984. In 1985/86 he was a post-doc at the Jet Propulsion Laboratory . Since 1985 he has been a researcher at the CNRS at the Bureau des Longitudes, and since 1994 as Research Director of the CNRS at the Paris Observatory. Since 1992 he has headed a celestial mechanical working group at the Paris Observatory.

Act

Laskar developed simulation methods in celestial mechanics supported by extensive computer algebra calculations. In 1989 he simulated the solar system (excluding Pluto ) over 100 million years into the future and past, finding evidence of chaotic behavior. The timescale for the development of chaotic behavior (corresponding to the Lyapunov exponent ) is 4 to 5 million years, so that in this case it is impossible to make predictions for a few tens of millions of years. These long-term simulations were confirmed by Jack Wisdom and Gerald Jay Sussman in 1992.

In 1993 he showed the instability of the axes of rotation of the inner planets Earth, Mars , Venus , and Mercury . For example, he showed that without the action of the moon, the inclination of the earth's axis would fluctuate from zero to 85 degrees, and that the inclination of the axis of rotation of Mars varied from zero to 60 degrees in the past, with corresponding effects on the climate of Mars . He was also able to justify the retrograde rotation of Venus from passages through chaotic zones in the long-term development.

In simulations of the solar system over 5 billion years, which he carried out in 2008, he found indications not only of a possible collision of Mercury with Venus or the sun, which had been suspected for a long time because of the resonance with Jupiter, but in a simulation even a destabilization of all inner planets (Mercury , Venus, Earth) in 3.3 billion years with the possibility of collisions of the inner planets with the earth. The calculations were more accurate than previous simulations (which used averaging) and included general relativistic effects and the moon.

Laskar applied the frequency analysis methods he developed in celestial mechanics to the stability of particle accelerator orbits and galaxy dynamics.

In 1993 he received the IBM Prize and the Prix G. de Pontécoulant of the French Academy of Sciences ( Académie des sciences ). In 1994 he received the CNRS silver medal. In 1996 he gave one of the plenary lectures at the second European Congress of Mathematicians in Budapest ( Stability of the Solar System ). He has been a corresponding member of the French Academy of Sciences since 1997 and a full member since 2003. In 2002 the asteroid (18605) Jacqueslaskar was named after him. In 2007 he received the Brouwer Award from the American Astronomical Society . For 2019 he was awarded the Milutin Milankovic Medal of the European Geosciences Union .

Web links

Individual evidence

  1. ↑ Laskar A numerical experiment on the chaotic behavior of the Solar System , Nature, Vol. 338, 1989, pp. 237-238. Laskar The chaotic motion of the Solar System. A numerical estimate of the size of the chaotic zones , Icarus, Vol. 88, 1990, pp. 266-291. Laskar Large scale chaos in the solar system , Astron. Astrophys., Vol. 287, 1994, L 9 -L12
  2. ↑ Laskar, F. Joutel, P. Robutel Stabilization of the earths obliquity by the Moon , Nature Vol. 361, 1993, pp. 615-617
  3. ↑ In contrast to the other planets and most moons, the sense of rotation is not in the same direction as the sense of rotation around the sun
  4. ↑ Laskar, Robutel The chaotic obliquity of the planets , Nature Vol. 361, 1993, p. 608. Laskar, A. Correia The four final rotation states of Venus , Nature, Vol. 411, 2001, pp. 767-770
  5. ↑ Laskar, M. Gastineau, Letters to Nature, June 11, 2009. 2600 orbits were simulated, which are compatible with the values ​​known today for the initial conditions and the orbit parameters. About one percent showed such an increase in the eccentricity of Mercury that a collision is possible
  6. ↑ Laskar, S. Dumas Global dynamics and long time stability in hamiltonian systems via numerical frequency analysis , Physical Review Letters, Vol. 70, 1993, p. 2975. Laskar Frequency analysis of multi-dimensional systems. Global dynamics and diffusion , Physica D, Vol. 67, 1993, pp. 257-281
  7. ↑ Minor Planet Circ. 45340
personal data
SURNAME Laskar, Jacques
BRIEF DESCRIPTION French astronomer
DATE OF BIRTH April 28, 1955
PLACE OF BIRTH Paris