Patrick Valageas web page

In collaboration with T.F. Stepinski I have studied the dynamics of solids in gaseous protoplanetary disks. Such disks appear after the collapse of an unstable gas cloud which forms a central star and a lighter but very extended disk (because of the conservation of angular momentum). It is beleived that the dust particles coagulate in the disk after successive collisions to build the planets we observe today. This is why the orbits of different planets in the solar system are almost coplanar. At a smaller scale the rings of Saturn are also the result of such processes.

In this work we studied how dust particles coagulate while they diffuse and are advected in the disk. We showed that the radial distribution of solids follows a different evolution than the one of the gas as soon as particles reach sizes of the order of a few centimetres. In some cases all the solid matter is accreted onto the star. Moreover, in a more realistic model some collisions could lead to fragmentation rather than coagulation. Therefore, the formation of planets by collisional coagulation seems a difficult process. This remains an open problem which has not received a fully satisfactory answer yet.

Articles:

• 1997, A&A, 319, 1007
• 1996, A&A, 309, 301