Protoplanetary disks around young stars are the birthplaces of planets. The structure of these disks and their lifetime determine when, where, and what kinds of planets can form. Therefore, our understanding of how planets form requires a clear picture of the evolution of the gas and dust in protoplanetary disks. While dust evolution has been intensely studied—thanks in large part to high-resolution observations from ALMA—our understanding of the gas, which makes up the bulk part of the disk mass, remains limited.
Gas plays an important role in almost every step of planet formation: it regulates the movement and evolution of dust grains, fuels the growth of planetary atmospheres, and governs the migration of young planets. The mass and size of the gas disk are especially critical. They influence whether a planet becomes a gas giant, an icy giant, or a rocky super-Earth, and whether it forms at all. However, direct measurements of disk gas mass—and its evolution over time—have lagged behind dust constraints, leaving a major gap in our understanding.
A key challenge lies in deciphering how protoplanetary disks evolve over their 1-10 million-year lifetimes. Competing theories—such as evolution driven by turbulent viscosity or by magneto-hydrodynamic (MHD) disk winds—make different predictions about how disk gas disperses and how disk sizes change with time. Population studies of disk fractions and dust masses suggest that disks evolve, but they do not directly constrain the behavior of the gas component.
To fill this critical gap, we put forward AGE-PRO, the ALMA survey of Gas Evolution in PROtoplanetary disks, that systematically surveys the gas in 30 protoplanetary disks spanning ages from 0.5 to 6 million years. The two major goals of our program are:
✩ Build a legacy dataset of high-quality molecular line observations that allow robust and uniform measurements of gas masses and sizes across the disk lifetime.
✩ Test theoretical models of global disk evolution—such as viscous accretion and MHD-driven winds—by comparing their predictions to observed trends in gas mass and disk size with age.
By directly tracing the gas evolution of disks over time, AGE-PRO provides essential constraints for the physical processes that govern disk dispersal and planet formation. Its results serve as a cornerstone for future work connecting disk evolution to planetary architectures, and offer a new empirical foundation for interpreting observations from ALMA, JWST, and beyond.
