2025ApJ...989...30Z

We report the serendipitous detection of the SO J_N = 6₅-5₄ (219.949 GHz) rotational transition in archival Atacama Large Millimeter/submillimeter Array observations of the spiral hosting protoplanetary disks around CQ Tau (with ≈4.9σ significance) and MWC 758 (with ≈3.4σ significance). In the former, the SO emission comes in the shape of a ring, arises from the edge of the continuum cavity, and is qualitatively consistent, at the currently available spectral resolution, with being in Keplerian rotation. In the latter, instead, while arising primarily from inside the continuum cavity, the SO emission also extends to the continuum ring(s), and its morphology and kinematics are less clear. We put these sources in the context of the other protoplanetary disks where SO detections have been previously reported in the literature and discuss the possible origins of SO in terms of (thermal) desorption or formation in the gas-phase. We argue that these processes might be fostered by dynamical perturbations caused by unseen embedded massive companions, shadows, or late-time infall, thus suggesting a possible link between perturbed dynamics and SO emission in (these) protoplanetary disks. If confirmed, our interpretation would imply that chemical evolution timescales could be significantly shorter in these systems than is commonly assumed, indicating that dynamical perturbations might influence the composition of newborn (proto)planets by altering the volatile makeup of their formation environment.