This parameter indicates the timescale over which the planet masses are “turned on” for the potential evaluation at the begining of a simulation, in orbital timescales at . The tapering function is the one of the [EU Test Comparison problem->http://www.astro.su.se/groups/planets/comparison/]. Note that the tapering is just applied at the potential evaluation, and not through the full hydro timestep. In particular the torque values output during the mass tapering should not be trusted. This parameter defaults to 0 (full planet masses applied straight away).