Transition disks as test laboratories for planet formation mechanisms

Kees Dullemond
Zentrum f. Astron., Heidelberg






Until recently, theories of planet formation could only be tested by comparing their outcomes (the predicted masses and orbits of planets) to know exoplanet data. With the new observational facilities of ALMA and VLT-SPHERE it is, however, now possible to observe protoplanetary disks to such a level of detail that we can see some of the physical processes of planet formation in action. In particular the class of "transition disks" show many features that can be interpreted as resulting from the same physical processes that are also believed to play a key role in planet formation: vortices, spiral waves, dust trapping etc. In this talk I will discuss this new and fascinating link between theory and observations.

Dust coagulation at ice lines

Sebastian Stammler
Zentrum f. Astron., Heidelberg


Ice lines are thought to be preferential sites of planet formation. The idea is that particles that are subjected to radial drift move inwards through ice lines and lose their volatiles through evaporation. These volatiles can then diffuse backwards and re-condense on particles just outside the ice line leading to a faster particle growth. To test this hypothesis we performed self-consistent simulations of coagulation by solving the time evolution of a two-parameter particle distribution (mass and ice fraction) including radial drift and time-dependent evaporation/condensation in a viscously accreting disk. We focused on the CO ice line which is located at ~ 40 AU in a MMSN around a T Tauri star. There, particle growth is mostly hindered by inward drift instead of fragmentation. We did not find any significant solid material enhancement outside the ice line. We rather found a solid material depletion inside the ice line which is directly correlated to the CO content of the particles and therefore caused purely by the evaporation of CO. The reason for that is that backward diffusing volatile gas mostly condenses on particles close to their drift barrier causing them to drift even more rapidly inwards through the ice line. In this talk I will introduce our model and connect our results to recent observations.