Astro 2020 White Paper: Realizing the Unique Potential of ALMA to Probe the Gas Reservoir of Planet Formation Thematic Area: Star and Planet Formation

Understanding the origin of the astonishing diversity of exoplanets is a key question for the coming decades. ALMA has revolutionized our view of the dust emission from protoplanetary disks, demonstrating the prevalence of ring and spiral structures that are likely sculpted by young planets in formation. To detect kinematic signatures of these protoplanets and to probe the chemistry of their gas accretion reservoir will require the imaging of molecular spectral line emission at high angular and spectral resolution. However, the current sensitivity of ALMA limits these important spectral studies to only the nearest protoplanetary disks. Although some promising results are emerging, including the identification of the snowlines of a few key molecules and the first attempt at detecting a protoplanet’s spiral wake, it is not yet possible to search for these important signatures in a diverse population of protoplanetary disks. Harnessing the tremendous power of (sub)mm observations to pinpoint and characterize the chemistry of planets in formation will require a major increase of ALMAs spectral sensitivity (5 − 10×), increase in bandwidth (2×) at high spectral resolution, and improved angular resolution (2×) in the 2030 era. ar X iv :1 90 3. 11 69 2v 1 [ as tr oph .S R ] 2 7 M ar 2 01 9