Cosmic Dust and Laboratory Simulation: Wishes, Results and Open Problems

Abstract

Cosmic dust plays an active role in several processes occurring in the interstellar medium, in star formation regions and around evolved stars. Thus, the identification of its properties is one of the major goals of modern astrophysics. In this framework, laboratory experiments are a fundamental tool, which allows us to interpret observations and to validate theoretical models on a quantitative basis. This is the reason why, in the recent years, a new generation of “laboratory astrophysics” has grown up, aimed at performing systematic experiments under carefully controlled and reproducible conditions. The goal is to make comparative analyses between samples produced and processed under different ambient conditions, which may reproduce — at the best we can do in a laboratory on Earth — the actual space environment. In this paper we intend to give an overview of recent results obtained in the Cosmic Physics Laboratory in Naples on several soot samples. A key of interpretation which correlates dust optical behaviour to structural properties in a self-consistent scenario will be discussed. This is a sort of evolutionary progression, which is linked both to production conditions and to processing mechanisms, such as thermal annealing, UV irradiation and ion bombardment. The derived general principles may be applicable to interpret spectral behaviours observed in different astronomical environments for carbon-based materials: interstellar and circumstellar media, cometary and interplanetary environments. Of course, several uncertainties still remain, especially concerning both the mass budget available in space as solid condensed forms and the aggregation status of cosmic dust. From the experimental point of view, many points are not fully clarified and require further analyses to remove several question marks. In this sense, a new plan of laboratory activities, based on innovative techniques, has to be developed to perform significant steps ahead. This in the view of pursuing new frontiers along the line that should bring to a consistent interpretation of physical and chemical phenomena involving cosmic dust.