Estimating the mass of the debris disc in HD 69830
  We present a method to estimate the mass of the debris disc in the HD 69830 system, which also hosts three exoplanets with Neptune-like minimum masses. By considering the range of published stellar ages, we interpret the infrared emission from the debris disc as originating from a steady state, collisional cascade of dust grains. Using dynamical survival models subjected to observational constraints, we estimate the allowed range of disc masses. If the disc has an age of about 1 Gyr, then its mass is several times that of our asteroid belt. The maximum allowed age for the disc and the number of planetesimals it contains are determined by the assumed value for the binding energy of the planetesimals. If one insists on interpreting the disc as being transient, then this mass estimate becomes an upper limit. 
Kevin Heng
astro-ph.GA astro-ph.EP