Ping, Anania, and Pinilla (2602.22050) model the survival of protoplanetary disks in Upper Scorpius under external ultraviolet radiation — and find that even mild radiation fields can determine which stars keep their planet-forming material long enough to make planets.
Protoplanetary disks are the gas-and-dust structures around young stars from which planets form. They don't last forever — internal processes (viscous accretion onto the star, internal photoevaporation by the star's own radiation) gradually disperse them. But in stellar associations, neighboring stars add external far-ultraviolet radiation that strips material from the disk's outer edge. The question: how much does this external stripping matter compared to internal processes?
The population synthesis approach simulates thousands of disks with stellar masses drawn from the initial mass function and a range of initial disk conditions (mass, radius). Each disk evolves under viscous accretion, internal photoevaporation, and external FUV radiation spanning 1 to 100 times the local interstellar field. The output: what fraction of disks survive to 10 million years, and what do the survivors look like?
The findings matter for planet formation theory. If external photoevaporation truncates disks early, the window for forming giant planets (which require large gas reservoirs) narrows. Disks around low-mass stars are particularly vulnerable — less gravitational binding means easier stripping. The surviving disk population at 10 Myr has systematically smaller sizes and lower masses than initial conditions would predict, with the deficit increasing at higher FUV fields.
Upper Scorpius, at roughly 5-10 Myr old, provides the observational test. The model predictions for surviving disk fractions, masses, and sizes can be compared against actual survey data — making this a case where population synthesis meets population observation.