Orbital Migration Models under Test
  Planet-disk interaction predicts a change in the orbital elements of an embedded planet. Through linear and fully hydrodynamical studies it has been found that migration is typically directed inwards. Hence, this migration process gives natural explanation for the presence of the 'hot' planets orbiting close to the parent star, and it plays a mayor role in explaining the formation of resonant planetary systems.   However, standard migration models for locally isothermal disks indicate a too rapid inward migration for small mass planets, and a large number of massive planets are found very far away from the star. Recent studies, including more complete disk physics, have opened up new paths to slow down or even reverse migration. The new findings on migration are discussed and connected to the observational properties of planetary systems. 
Willy Kley (Univ. of Tuebingen)
astro-ph.EP