(a) Example of a measured image for particle sizes, with corrected brightness and contrast. The yellow circles indicate a measured particle. The solid red arrow indicates an example of a particle that is too malformed to be counted. The dashed blue arrow indicates a particle that is obscured but can be measured by fitting the circle perimeter to the visible particle edges (<2% of particles counted). The hollow green arrow indicates a particle that is not perfectly spherical, but has a counted diameter using the equivalent circular diameter (<1% of particles counted). (b) Gold-coated tholin particle with sufficient resolution to image and count the tholin monomers, one of which is outlined in red. The monomers are the smaller units with clear separations that constitute the larger, spherical tholin particle. (c) Particle size distributions for HP (blue) and LP (red) aggregates. 1481 HP and 1065 LP particles were counted to create statistically significant sample sizes. The overlaid curves are the kernel density estimations of the histograms, using a Gaussian kernel.