Molecular snow lines in protoplanetary disks

Abstract

Compared to the Sun and to the gas+dust compn. of the interstellar medium from which the solar system formed, the Carbon and Nitrogen content of the bulk silicate Earth (mantle+hydrosphere+atm.) is reduced by several orders of magnitude, relative to Silicon. Evidence from primitive bodies as a function of distance from the Sun suggests that at least part of this depletion must occur early in the process of planetesimal assembly. With pioneering IR and (sub)mm observations such as those enabled by ground-based 8-10m class telescopes (and in future the James Webb Space Telescope) and the Atacama Large Millimeter Array (ALMA), we can now examine the principal volatile reservoirs of gas rich disks as a function position within the disk and evolutionary state. Key to these studies is the concept of condensation fronts, or 'snow lines,' in disks - locations at which key volatiles such as water, carbon monoxide, or nitrogen first condense from the gas. This talk will review the observational characterization of snow lines in protoplanetary disks via both gas and dust tracers, esp. recent ALMA observations, and highlight links to theor. investigations that are needed to tie the observational results to the delivery of volatiles to planetary surfaces in the habitable zones around Sun-like stars.