The Chemistry of Planet Formation: Chemical Substructures at 10 au Scales in Protoplanetary Disks from the ALMA MAPS Large Program

Planets form and obtain their compositions in dust- and gas-rich disks around young stars. This process is intimately connected to the spatial arrangement of disk material. While dust substructure at the 1-10 au scale is commonly seen in these disks, but far fewer observations have probed gas substructure at similar scales. To address this, the Molecules with ALMA at Planet-forming Scales (MAPS) Large Program provides a detailed, high resolution (~10–20 au) view of molecular line emission in five protoplanetary disks at spatial scales relevant for planet formation. Here, we present a systematic analysis of chemical substructures in 18 molecular lines toward the disks around IM Lup, GM Aur, AS 209, HD 163296, and MWC 480, with each source showing evidence of ongoing planet formation. We identify more than 200 chemical substructures, which are found at nearly all radii where line emission is detected. A wide diversity of radial morphologies, including rings, gaps, and plateaus, is observed both within each disk and across the MAPS sample. This diversity in line emission profiles is also present in the innermost 50 au and suggests that planets form in varied chemical environments both across disks and at different radii within the same disk. Moreover, the identification of significant reservoirs of several large organic molecules located in the inner 50-100 au of these disks implies that nascent planets may form in environments rich with precursors of life-essential molecules. Overall, the MAPS program has demonstrated the utility of using chemical substructures as probes of disk physical characteristics and the necessity of sensitive, high angular resolution observations of molecular line emission in revealing the chemical conditions in which planets are born.