Chemical diversity of organic volatiles among comets: An emerging taxonomy and implications for processes in the proto-planetary disk

Abstract

As messengers from the early Solar System, comets contain key information from the time of planet formation and even earlier – some may contain material formed in our natal interstellar cloud. Along with water, the cometary nucleus contains ices of natural gases (CH₄, C₂H₆), alcohols (CH₃OH), acids (HCOOH), embalming fluid (H₂CO), and even anti-freeze (ethylene glycol). Comets today contain some ices that vaporize at temperatures near absolute zero (CO, CH₄), demonstrating that their compositions remain largely unchanged after 4.5 billion years. By comparing their chemical diversity, several distinct cometary classes have been identified but their specific relation to chemical gradients in the proto-planetary disk remains murky. How does the compositional diversity of comets relate to nebular processes such as chemical processing, radial migration, and dynamical scattering? No current reservoir holds a unique class, but their fractional abundance can test emerging dynamical models for origins of the scattered Kuiper disk, the Oort cloud, and the (proposed) main-belt comets. I will provide a simplified overview emphasizing what we are learning, current issues, and their relevance to the subject of this Symposium.