Satellite formation from planetary rings : the fascinating case of Saturn, and beyond.

Séminaire IPAG de Aurélien Crida (OCA), jeudi 7 février 2013 à 11h00, IPAG seminar room

In the rings of Saturn, self gravity is dominated by the tidal forces from the planet. Therefore, the boulders consituting the rings can not aggregate. However, the rings evolve viscously and spread (e.g. Salmon et al. 2010). As they spread beyond the Roche radius, the tides become weaker than the self gravity, and new satellites form. I will describe this process, and show that the regular satellites of Saturn most likely formed this way (Charnoz et al. 2010, 2011).

Then, I’ll present an analytical, general model of this process (Crida & Charnoz 2012). We demonstrate that the spreading of rings beyond the Roche radius leads to the formation of a satellite system with a precise mass-distance distribution. This distribution fits very well that of the regular satellites of Saturn. SURPRISE 1 : Uranus and Neptune’s regular satellites follow the same distribution... Did they have massive rings ? SURPRISE 2 : If the rings are more than 1% of the planet mass, our model predicts the formation of 1 single large satellite, like Charon or our Moon !

Conclusion : The spreading of rings beyond the Roche radius may be the most general process of satellite formation in the Solar System.