Is it necessary to go beyond the ponctual mass approximation for tidal   perturber in close systems?
  With the discoveries of very close star-planet systems with planet orbiting sometimes at several star radius but also with well-known situations in our solar system where natural satellites are very close to their parent planet the validity of the ponctual mass approximation for the tidal perturber (respectively the parent star or planet when we study the close planet or natural satellite dynamics) has to be examined. In this short paper, we consider this problematic using results coming from a complete formalism that allows to treat the tidal interaction between extended bodies. We focus on its application to a simplified configuration. 
Stephane Mathis and Christophe Le Poncin-lafitte