An international team of astronomers has captured rare images of planetary systems during a "little-explored" evolutionary stage: planetary adolescence. Conducted through the ARKS project (ALMA survey to Resolve exoKuiper belt Substructures), the study utilized the power of the Atacama Large Millimeter/submillimeter Array (ALMA) to peak into this transition phase.
The research is led by Chilean astronomer Sebastián Marino (University of Exeter and external researcher at the YEMS Millennium Nucleus) and features key contributions from YEMS researchers at the University of Santiago, Chile (Usach).
A Missing Link in Planet History
The disks observed by ARKS are debris disks: belts of dust and debris that remain around a star once its planets have already formed. This stage is analogous to adolescence in the life of a planetary system: more evolved than protoplanetary disks (where planets are still forming), but still far from a stable configuration (such as the Solar System).
“We often observe the ‘baby photos’ of forming planets, but planetary adolescence was the missing link,” explains Meredith Hughes, one of the project’s co-principal investigators.
In our own Solar System, this phase is represented by the Kuiper Belt, a region beyond Neptune that bears traces of violent collisions and planetary migrations that occurred billions of years ago.
Light Disks, Complex Structures
Debris disks are extremely faint—hundreds or even thousands of times dimmer than the protoplanetary disks where planets are born—making them exceptionally difficult to observe. However, thanks to ALMA’s unprecedented resolution, the ARKS team revealed a surprising diversity of structures, including multiple rings, extended halos, abrupt edges, asymmetries, arcs, and clumps.
“We are not seeing simple rings, but complex and dynamic systems that reveal a violent stage in the history of these planets,” notes Sebastián Marino, a YEMS external researcher and leader of the ARKS program.
Outstanding contribution by YEMS–Usach
The ARKS project features the participation of YEMS Millennium Nucleus researchers based at the CIRAS Center and the Department of Physics at Usach:
-Sebastián Pérez, Usach faculty member, YEMS acting director, and project researcher.
-Philipp Weber, YEMS-Usach postdoctoral researcher and ARKS team member.
-Fernando Castillo, YEMS-Usach Master’s student in Astrophysics and active participant in scientific analysis.
This contribution reinforces YEMS’s role as a key player in cutting-edge research on the formation and evolution of planetary systems.
Key Findings of the ARKS Project
-New observational standard: ARKS presents the highest-resolution observations of debris disks to date.
-Turbulent youth: Nearly one-third of the disks display clear substructures such as multiple rings.
-Unexpected diversity: While some disks have complex structures, others evolve into broad, smooth belts.
-Surviving gas: Residual gas was found in several systems, which could affect the chemistry and dynamics of the planets.
-Open data: All ARKS observations and processed products are available to the public.
A Mystery Observed by ALMA and Explained by Usach
One of the most intriguing scientific challenges of the ARKS project was confronting a completely unexpected observation: one of the debris disks exhibits a strong asymmetry, with a localized accumulation of rocks and dust resembling a dense cloud of debris. This type of structure is particularly difficult to explain at this stage of evolution, as disks are typically expected to be symmetrical.
Faced with this mystery, YEMS–Usach researchers led one of the central scientific papers of the ARKS project, proposing an explanation based on the interaction between solid debris and the small amount of gas still present in the disk. The study explores the feasibility of forming debris vortices that can concentrate solid material over long periods.
“These observations force us to rethink the role that even a minimal amount of gas can play in disks we previously believed were almost entirely dominated by solids. The possibility of debris vortices opens up a new, dynamic scenario for understanding these asymmetries,” explains Sebastián Pérez, a professor at Usach and deputy director of the Millennium YEMS Center.
“While ALMA observations clearly show that gas exists in some extrasolar Kuiper belts, we still don’t know for certain whether the amount we detect represents all the gas present, or if there is an additional, invisible fraction that escapes direct measurement. By carefully studying the conditions under which these structures form, we can use the disk itself as a laboratory to infer the true amount of gaseous matter and how the system has evolved,” explains Philipp Weber, a YEMS-Usach researcher who led one of the ten papers published on Tuesday.
Was our Solar System the Norm or the Exception?
The results suggest that this adolescent stage is marked by planetary migrations, massive collisions, and intense orbital rearrangement, similar to the events that gave rise to the Moon.
“These disks record a time when planetary orbits were being chaotically rearranged,” explains Luca Matrà, co-lead author of the study.
Looking to the Future
The legacy of the ARKS project will be essential for identifying young, as-yet-invisible planets and for understanding how planetary families form and evolve.
“It’s like adding the missing pages to the Solar System’s family album,” Hughes concludes.