ALMA Reveals Lives of Planet-Forming Disks

Observations of 30 disks reshape our understanding of how gas evolves in the birthplaces of planets

An international team of astronomers has unveiled groundbreaking findings about the disks of gas and dust surrounding nearby young stars using the Atacama Large Millimeter/submillimeter Array (ALMA). These results, published in 12 papers in a special issue of The Astrophysical Journal, are part of an ALMA Large Program known as AGE-PRO (ALMA Survey of Gas Evolution of PROtoplanetary Disks).

AGE-PRO observed 30 protoplanetary disks around Sun-like stars to measure gas disk masses at different stages of evolution. The study revealed that gas and dust in these disks evolve at different rates. “AGE-PRO provides the first systematic measurements of gas disk masses and sizes across the lifetime of planet-forming disks,” said Ke Zhang, Principal Investigator of the program from the University of Wisconsin–Madison.

A protoplanetary disk surrounds its host star for several million years, during which time its gas and dust evolve and dissipate. This sets the timeline for the formation of giant planets. The initial mass, size, and angular momentum of the disk strongly influence the kind of planets that can form—whether gas giants, icy giants, or mini-Neptunes—and their potential migration paths.

ALMA’s unique sensitivity enabled the team to detect faint molecular lines, which allowed them to probe the cold gas within the disks. AGE-PRO targeted 30 disks of different ages, ranging from less than one million to over five million years old, located in three star-forming regions: Ophiuchus, Lupus, and Upper Scorpius. The survey captured key tracers of gas and dust masses, building a legacy dataset for studying the full lifecycle of planet-forming environments.

While carbon monoxide (CO) is the most widely used tracer in protoplanetary disks, AGE-PRO also employed the molecular ion N₂H⁺ to improve the accuracy of gas mass estimates. Additionally, ALMA’s sensitivity enabled the serendipitous detection of other molecular lines, including H₂CO, DCN, DCO⁺, N₂D⁺, and CH₃CN. “This is the first large-scale chemical survey of its kind, targeting 30 disks spanning a broad age range to characterize gas masses,” said John Carpenter, ALMA Observatory Scientist and co-lead of the program.

The findings reveal that gas and dust are consumed at different rates as disks age, with a distinct “swing” in the gas-to-dust mass ratio over time. Zhang explains, “The most surprising finding is that although most disks dissipate after a few million years, those that survive retain more gas than we expected. This fundamentally alters our understanding of how and when planets acquire their final atmospheres.”

Among the collaborators in AGE-PRO was a prominent Chilean team from the University of Chile, led by astrophysicist Laura Pérez, along with postdoctoral researchers Carolina Agurto and Aníbal Sierra, all of whom affiliated with the Center for Astrophysics and Associated Technologies (CATA). Pérez emphasized the value of the survey in providing a much-needed view of gas evolution: “Until now, most of what we knew about disk evolution was based on solids. With AGE-PRO, we finally have direct, consistent measurements of how the gas evolves throughout the disk’s lifetime—crucial for understanding how giant planets form.”

Carolina Agurto led the analysis of Upper Scorpius, a region known for hosting more evolved disks. Her work delivered critical insights into the final stages of these systems, showing that disks that persist longer contain significantly more gas than previously thought. Meanwhile, Aníbal Sierra focused on one of the brightest and oldest disks in the sample—2MASS J16120668-3010270—where he identified signs of two forming planets: one revealed by the surrounding dust and another inferred from gravitational perturbations. Follow-up observations with the James Webb Space Telescope (JWST) are already being planned to directly detect exoplanets.

Several undergraduate and graduate students in Chile also contributed to AGE-PRO: Benjamín Cabrera, who worked on determining stellar masses; José Mondaca, who analyzed the youngest disks in Ophiuchus; and Camila Pulgarés, who focused on the evolutionary study of dust in all 30 disks.

“The advancement of science is a truly collaborative endeavor, driven by people from different countries and backgrounds, each contributing their unique perspective to push the boundaries of discovery,” said Ilaria Pascucci, co-Principal Investigator from the University of Arizona.

Additional Information

The original press release was published by the National Radio Astronomical Observatory (NRAO) of the U.S.A., an ALMA partner on behalf of North America.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan, and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of ALMA's construction, commissioning, and operation.

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