Astronomy Colloquium - Ilse Cleeves

The last decade of ALMA observations has transformed our view of planet-forming environments. High-resolution images have revealed structured belts of millimeter-sized dust and distinct molecular compositions, both within individual disks and between disk systems. How does this diversity translate into the initial conditions for planet formation, and into the gas and solids that planets ultimately receive? Answering this requires moving beyond the handful of bright, well-studied disks to the typical disks around the stars known to host planets. I will present results from the ALMA “Disk–Exoplanet C/Onnection” (DEC/O) Large Program, the largest chemical survey of planet-forming disks to date, which covers 80 disks around K and M stars in four nearby star-forming regions. DEC/O finds that most disks have elevated C/O ratios in their molecular layers. This is driven by the preferential loss of oxygen as water-rich ices are carried toward the midplane by growing dust. Disk structure and dust evolution, rather than the host star or birth environment, appear to shape this chemistry, while late infall of fresh material can reset it. Combined with JWST and Keck spectroscopy, DEC/O also reveals the first statistical links between the composition of the outer disk and the inner regions where planets form. I will conclude with a look forward to measuring disk gas masses directly with far-IR observations of HD from the NASA POEMM balloon mission and the newly selected PRIMA probe, and to faster, deeper chemical surveys enabled by the ALMA Wideband Sensitivity Upgrade.