Dynamical Processes in the Early Solar System

A. Morbidelli (OCA, Nice, France)


We review our understanding of the dynamical processes that led to the formation of the 
Solar System as we know it now, and compare the main stages of Solar System evolution to 
those of known extra-solar systems, enlightening differences and/or similarities.

We begin by discussing the stellar environment in which the Solar System formed. The 
discovery of the first object (i.e. Sedna) at the inner boundary of the Inner Oort Cloud 
allows us to estimate the statistical frequency of stellar encounters and to deduce that 
Solar System formed in an environment of about 200-300 stars within ~0.2 parsecs.

Then we discuss the crucial issue of why our Solar System does not have a hot Jupiter 
planet. We argue that the most plausible reason can be found in the mass hierarchy of our 
giant planets. We will present new hydro-dynamical calculations showing several possible
resonant configurations of our 4 giant planets that are stable and avoid migration towards 
the Sun. Some of these configurations remain stable even after the disappearance of the gas 
disk.

Next, we discuss the clearing of the inner part of the disk (i.e. interior to the orbit of 
Jupiter) due to the formation of the terrestrial planets. The rapid decay of the number of 
planetesimals compares quite well with the rapid drop of mid-infrared emission of debris 
disks in the first 10-30 My.

Finally we will focus on the Late Heavy Bombardment. The evidence for a late cataclysmic 
bombardment episode on the terrestrial planets teaches us two things. First, planets can 
become temporarily unstable, more or less late in time, which might be linked with the 
origin of the large eccentricities of extra-solar planets. Second, our planetary system was 
probably surrounded by a massive disk of planetesimals, sharing some similarities with those 
of Fomalhaut and AU Mic, until the time of the LHB. The dust produced by this distant disk 
during its massive phase was comparable to that required to explain the brightness in the 
far-infrared of some debris disks around main sequence solar stars. The interaction between 
our giant planets and the disk could have led to the acquisition of their current orbit,
starting from one of the resonant, non-migrating configurations achieved during the 
evolution in the gas disk. We will discuss different possible outcomes, depending on disk 
mass and radial extent, that might explain observed extra-solar disks.