When
3:30 p.m., April 17, 2008
Where
Kuiper Space Sciences 308
Alessandro Morbidelli of Observatoire de la Côte d'Azur/SWRI, will discuss: “Towards a Coherent Picture of the Dynamical Evolution of the Outer Solar System.”
Abstract
I will start presenting our model for the origin of the Late Heavy Bombardment (LHB) of the terrestrial planets, sometimes called “the Nice model”. This model argues that the giant planets had initially quasi-circular and co-planar orbits and orbital separations much smaller than today. They were surrounded by a massive planetesimal disk, extended up to 30--35~AU. As a consequence of the interaction of the planets with the planetesimal disk, the giant planets suffered orbital migration, which slowly increased their orbital separation. If the ratio of the orbital periods of Saturn and Jupiter was initially less than 2, these planets had to cross eventually their mutual 1:2 mean motion resonance, thereby triggering a global instability in the planetary motion. The current orbital configuration could then be achieved from the gravitational interaction between the planets and the disk particles. The LHB would have been caused by the consequent dispersion of the trans-Neptunian planetesimals, but also by the escape of ~90% of the main belt asteroids, during a phase of fast planet migration that followed the 1:2 resonance crossing. The model also explains the current structure of the Kuiper belt, and the capture of some primordial trans-Neptunian objects on orbits typical of the Trojans of the giant planets, irregular satellites and
outer main belt asteroids.
The main weakness of the Nice model is that the initial conditions of the giant planets were just postulated. More recently, we have studies the dynamics of the giant planets embedded in the proto-planetary gas disk, using hydro-dynamical simulations. The only systems that we found to reach a steady state are those in which the planets are locked in a quadruple mean motion resonance (i.e. each planet is in resonance with its neighbor). In total we found 6 such configu-rations. For some gas disk parameters, these configurations are characterized by a negligible migration rate, thus explaining why there are no “hot Jupiters” in our Solar System. After the disappearance of the gas, and in absence of planetesimals, only two of these six configurations (the least compact ones) are stable for a time of hundreds of millions of years or more. I will explain how these two configurations can lead to an evolution similar to that described by the Nice model, which removes the arbitrary character of the initial conditions in our original work.
Refreshments will be served at 3:15 p.m. in the Atrium.
Abstract
I will start presenting our model for the origin of the Late Heavy Bombardment (LHB) of the terrestrial planets, sometimes called “the Nice model”. This model argues that the giant planets had initially quasi-circular and co-planar orbits and orbital separations much smaller than today. They were surrounded by a massive planetesimal disk, extended up to 30--35~AU. As a consequence of the interaction of the planets with the planetesimal disk, the giant planets suffered orbital migration, which slowly increased their orbital separation. If the ratio of the orbital periods of Saturn and Jupiter was initially less than 2, these planets had to cross eventually their mutual 1:2 mean motion resonance, thereby triggering a global instability in the planetary motion. The current orbital configuration could then be achieved from the gravitational interaction between the planets and the disk particles. The LHB would have been caused by the consequent dispersion of the trans-Neptunian planetesimals, but also by the escape of ~90% of the main belt asteroids, during a phase of fast planet migration that followed the 1:2 resonance crossing. The model also explains the current structure of the Kuiper belt, and the capture of some primordial trans-Neptunian objects on orbits typical of the Trojans of the giant planets, irregular satellites and
outer main belt asteroids.
The main weakness of the Nice model is that the initial conditions of the giant planets were just postulated. More recently, we have studies the dynamics of the giant planets embedded in the proto-planetary gas disk, using hydro-dynamical simulations. The only systems that we found to reach a steady state are those in which the planets are locked in a quadruple mean motion resonance (i.e. each planet is in resonance with its neighbor). In total we found 6 such configu-rations. For some gas disk parameters, these configurations are characterized by a negligible migration rate, thus explaining why there are no “hot Jupiters” in our Solar System. After the disappearance of the gas, and in absence of planetesimals, only two of these six configurations (the least compact ones) are stable for a time of hundreds of millions of years or more. I will explain how these two configurations can lead to an evolution similar to that described by the Nice model, which removes the arbitrary character of the initial conditions in our original work.
Refreshments will be served at 3:15 p.m. in the Atrium.
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