The ISD size distribution from astronomical models and in situ data by Ulysses (from Sterken et al. in preparation). The smallest ISD particles are the most numerous. Distributions derived from astronomical observations were taken from Wang et al. (2015), Grün & Landgraf (2000), Weingartner & Draine (2001). Ulysses data are from Krüger et al. (2015).