A new study utilizing the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile's Atacama Desert has uncovered complex rings, gaps, and cavities within previously smooth, compact planet-forming disks, challenging long-held assumptions about how planetary systems originate.
For years, astronomers observed that while large protoplanetary disks surrounding young stars featured dramatic rings and dark gaps, many smaller stellar nurseries appeared surprisingly plain and featureless. This created a puzzle over whether compact disks represented a fundamentally different type of planet-forming system or if critical details were simply missing from view.
To investigate this mystery, a research team led by Pietro Curone of CATA and the Universidad de Chile—alongside colleagues Gijs Mulders, Nienke van der Marel, and Laura Pérez—focused on 11 very small protoplanetary disks located within the Lupus star-forming region. By configuring ALMA with its most extended antenna arrangement at a wavelength of approximately 0.9 mm, the team achieved an unprecedented angular resolution of roughly 0.02 arcseconds, translating to a linear scale of about 2 astronomical units (AU).
The ultra-sharp observations revealed that at least part of the previous simplicity was an illusion caused by resolution limits. Four of the eleven disks showed clear substructures within 10 AU of their central stars, with three additional systems displaying hints of similar architecture. For example, the system known as Sz 112 revealed a central cavity extending just 1.6 AU from its star. Researchers suggest these hidden rings and gaps could be signatures carved by forming super-Earths or mini-Neptunes, though further studies are required to confirm the exact mechanisms behind the newly revealed features.