Survival of Interstellar Organics in Protoplanetary Disks: Laboratory Experiments on Organic Ice Photostability

Harvard University, Cambridge MA

Investigators

Abstract

Following the collapse of a cloud core to form a star, the organic-rich icy grains can become incorporated into planet-forming disks, and the presence of large quantities of organic molecules may radically change the chemical trajectory of a forming planet or moon. It is currently unclear if these interstellar organic inventories survive the different stages of star and planet formation. This project will experimentally determine the UV and electron-induced photodissociation cross section of a range of common interstellar organics when embedded in interstellar ice analogs. The project will provide a first comprehensive view of the survival of interstellar organic molecules and organic functionality during disk formation. The project will train a graduate student and a postdoctoral researcher to be interdisciplinary scholars, crossing boundaries between chemistry and astronomy, theory and experiments. This project will experimentally explore the ice-phase UV and electron photodissociation cross sections and dissociation products of 15 organic molecules. The experiments will be carried out under ultra-high vacuum conditions using a pre-existing experimental set-up that enables the continuous monitoring of the ice composition using sensitive FTIR spectroscopy. The experiments will constrain the branching ratios for dissociation events into destruction vs. preservation of chemical functionality. The organic molecules are selected to explore how organic size and functionality affect their resistance to photo destruction, which will be used to make reasonable extrapolations to the complete interstellar organic inventory, thus enabling predictions of the overall interstellar organic survival up until incorporation into icy planetesimals. The immediate result will be a comprehensive database of dissociation cross sections for interstellar model organics across a range of relevant ice conditions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.