Search

Abstract: Since the discovery of the first extra-solar planets, we are confronted with the puzzling diversity of planetary systems. Processes like planet radial migration in gas-disks and planetary orbital instabilities, often invoked to explain the exotic orbits of the extra-solar planets, at first sight do not seem to have played a role in our system. In reality, though, there are several aspects in the structure of our Solar System that cannot be explained in the classic scenario of in-situ formation and smooth evolution of the giant planets. This article outlines a new view of the evolution of the outer Solar System that emerges from the so-called ‘Nice model’ and its recent extensions. The story provided by this model describes a very “dynamical” Solar System, with giant planets affected by both radial migrations and a temporary orbital instability. Thus, the diversity between our system and those found so far around other stars does not seem to be due to different processes that operated here and elsewhere, but rather stems from the strong sensitivity of chaotic evolutions to small differences in the initial and environmental conditions. [Copyright &y& Elsevier]

Abstract: The population of Near-Earth Objects (NEOs) evolves on orbits which can cross the orbit of the Earth. Most NEOs come from the asteroid belt via unstable zones associated with powerful or diffusive resonances. Their evolutionary paths and the statistical properties of their dynamics have been determined by massive numerical integrations. A steady-state model of their orbital and magnitude distributions has been elaborated which indicates that 1000 NEOs are kilometre-size with an impact frequency with the Earth around 0.5 Myr. A non-gravitational mechanism, the Yarkovsky thermal drag, plays the dominant role in delivering material in the NEO source regions, explaining how this population is maintained in a steady-state and why its size distribution is shallower than expected if NEOs were created through the direct injection of fresh fragments from collisional break ups into resonances. To cite this article: P. Michel et al., C. R. Physique 6 (2005). [Copyright &y& Elsevier]

Understanding how the Kuiper belt acquired its puzzling present orbital structure will provide insight into the formation of the outer planetary system and on its early evolution. We outline a scenario of primordial sculpting – issued from a combination of mechanisms proposed by various authors – that seems to explain most of the observed properties of the Kuiper belt. Several aspects are not yet totally clear, and some may not be totally correct. But, for the first time, we have a view – if not of the detailed sculpture – at least of its rough cast. To cite this article: A. Morbidelli, H.F. Levison, C. R. Physique 4 (2003). [Copyright &y& Elsevier]