Solar System Formation

Abstract

In this review, three major changes in our understanding of the early history of the Solar System are presented. 1) Early differentiation: A few recent results support the idea that protoplanet formation and differentiation occurred partly simultaneously than CAI formation. First, some iron meteorites, eucrites, and angrites older than the chondrules or even than the CAI have been found. Second, iron meteorites could be debris of early disrupted differentiated planetesimals, scattered from the terrestrial planet region to the Main Belt. Finally, chondrules contain fragments of planetesimal material. 2) Earth and Moon: An equilibration mechanism explains the identical Oxygen isotopic composition of the Earth and the Moon. In addition, it has been shown that the Earth and the Moon mantles have the same 182^W anomaly, in contrast to what was believed before. Consequently, the Moon forming impact should have occurred after the extinction of the 182Hf radioactivity, about 60 Myr after Solar System formation. This new datation is in agreement with new N-body numerical simulations of the last phase of terrestrial planets formation, in which giant impacts occur during about 100 Myr. 3) Giant planets and Nice model: The migration of the giant planets in the protoplanetary disc can be prevented if the planets are in resonance, close to each other. In the ``Nice model'', the 4 outer planets of the Solar System were in a compact configuration after the dissipation of gaseous disc. A few hundred million years later, a global instability drives the planets on their present orbits, producing the Late Heavy Bombardment. In this frame, a lot of characteristics of our Solar System can be explained.