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.
