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Published online by Cambridge University Press: 30 March 2016
A common origin of the sun and the planets from the collapse of interstellar gas is now widely accepted. Regardless of how stars form, which is considered as the previous step of the whole story, the starting point is a flattened rotating cloud containing a mixture of dusts and gas (the so called Kant-Laplace Nebula). On the other hand the observations of young solar-mass stars show with increasing evidence that the gas is dispersed away on a time scale less than 107 years and this provides us with a clear time constraint for model building since the formation of the giant gaseous planets have to take place on a shorter time scale.