Empirical constraints of fundamental properties of protoplanetary disks are essential for understanding planet formation and planetary properties1,2. Carbon monoxide (CO) gas is often used to constrain disk properties3. However, estimates show that the CO gas abundance in disks is depleted relative to expected values4,5,6,7, and models of various disk processes impacting the CO abundance could not explain this depletion on observed ~1 Myr timescales8,9,10,11,12,13,14. Here we demonstrate that surface energy effects on particles in disks, such as the Kelvin effect, that arise when ice heterogeneously nucleates onto an existing particle can efficiently trap CO in its ice phase. In previous ice formation models, CO gas was released when small ice-coated particles were lofted to warmed disk layers. Our model can reproduce the observed abundance, distribution and time evolution of gaseous CO in the four most studied protoplanetary disks7. We constrain the solid and gaseous CO inventory at the midplane and disk diffusivities and resolve inconsistencies in estimates of the disk mass—three crucial parameters that control planetary formation.
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The numerical models used in this work are not public. However, they are available from the corresponding author upon reasonable request.
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We acknowledge K. Öberg for her feedback on the surface binding properties of CO ice, S. Andrews for his insightful discussion of the outer radii of disks as measured from CO emission and J. Szulagyi for insightful discussions about the temperature structures in protoplanetary disks. This work benefited from the Exoplanet Summer Program in the Other Worlds Laboratory at the University of California, Santa Cruz, a program funded by the Heising–Simons Foundation. D.P. acknowledges support from the Ford Foundation Dissertation Year Fellowship Program and support from NASA (the National Aeronautics and Space Administration) through the NASA Hubble Fellowship grant HST-HF2-51490.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. D.P. and R.M.C. acknowledge support from NSF CAREER grant number AST-1555385. R.M.C and X.Z. acknowledge support from NASA Interdisciplinary Consortia for Astrobiology Research (ICAR) grant 80NSSC21K0597. P.G. acknowledges support from the 51 Pegasi b Fellowship sponsored by the Heising–Simons Foundation and support from NASA through the NASA Hubble Fellowship grant HST-HF2-51456.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. X.Z. acknowledges support from the NASA Solar System Workings Grant 80NSSC19K0791 and the NASA Exoplanet Research Grant 80NSSC22K0236. D.P. is an NHFP Sagan Fellow.
The authors declare no competing interests.
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Powell, D., Gao, P., Murray-Clay, R. et al. Depletion of gaseous CO in protoplanetary disks by surface-energy-regulated ice formation. Nat Astron 6, 1147–1155 (2022). https://doi.org/10.1038/s41550-022-01741-9