Exploring the dusty Universe

Dust is an ubiquitous inhabitant of the interstellar medium, and leaves an un- mistakable signature in its optical properties, and physico-chemical evolution. Although there is little direct knowledge of the true nature of interstellar dust grains, strong evidences point toward the possibility that such grains are composites of many small monomers (mainly made of silicates and carbonaceous materials). We consider two different mod- els of fluffy dust aggregates, occurring as result of ballistic particle-cluster and cluster- cluster aggregation, and a cluster with a Gaussian-like sphere size distribution. We study the optical properties of such composite structures through the multipole fields and the Transition Matrix approach. Our results show the severe limits of applicability of the ef- fective medium theories. By comparing radiation and gravitational forces, we also infer some relevant insights into the dynamical evolution of composite grains in the Solar Sys- tem. We finally explore the possible role of composite fluffy dust grains in igniting an extraterrestrial prebiotic chemistry.