The Chemistry of Protoplanetary Disks in Planet Formation: A Comprehensive Review

Protoplanetary disks are some of the most chemically rich and physically dynamic systems in the universe. Formed by the gravitational collapse of molecular clouds, these vast disks of gas and dust are where the raw ingredients of planets — and perhaps life — are assembled. This review surveys the structure and evolution of protoplanetary disks, covering temperature gradients, disk geometry, and radiation environments that together determine where and how planets are born. We then trace the astrochemical processes occurring within these disks: how molecules form, freeze, and react across different disk zones, and how snow lines for water, carbon monoxide, and methane shape the chemical makeup of forming planets. We highlight recent findings from ALMA and the James Webb Space Telescope, which have detected complex organic molecules in systems like PDS 70 — results that challenge classical astrochemical models. By examining the capabilities and gaps in models such as UCLCHEM, NAUTILUS, and DALI, we identify where current theory struggles to explain observations, particularly in the hot, turbulent inner disk. The review concludes by framing future directions in modelling, observation, and laboratory experiments as essential steps toward understanding not just planet formation, but the conditions that make habitable worlds possible. Prepared as part of an astrophysics internship programme (Edufabrica, IIT Guwahati context, 2024–25).