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While planets are commonly discovered around main-sequence stars, the processes leading to their formation are still far from being understood. Current planet population synthesis models, which aim to describe the planet formation process from the protoplanetary disk phase to the time exoplanets are observed, rely on prescriptions for the underlying properties of protoplanetary disks where planets form and evolve. The recent development in measuring disk masses and disk-star interaction properties, i.e., mass accretion rates, in large samples of young stellar objects demand a more careful comparison between the models and the data. We performed an initial critical assessment of the assumptions made by planet synthesis population models by looking at the relation between mass accretion rates and disk masses in the models and in the currently available data. We find that the currently used disk models predict mass accretion rate in line with what is measured, but with a much lower spread of values than observed. This difference is mainly because the models have a smaller spread of viscous timescales than what is needed to reproduce the observations. We also find an overabundance of weakly accreting disks in the models where giant planets have formed with respect to observations of typical disks. We suggest that either fewer giant planets have formed in reality or that the prescription for planet accretion predicts accretion on the planets that is too high. Finally, the comparison of the properties of transition disks with large cavities confirms that in many of these objects the observed accretion rates are higher than those predicted by the models. On the other hand, PDS70, a transition disk with two detected giant planets in the cavity, shows mass accretion rates well in line with model predictions.
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This content will become publicly available on April 1, 2026
The diversification and dissipation of protoplanetary disks
Protoplanetary disk evolution exhibits trends with stellar mass, but also diversity of structure, and lifetime, with implications for planet formation and demographics. We show how varied outcomes can result from evolving structures in the inner disk that attenuate stellar soft X-rays that otherwise drive photoevaporation in the outer disk. The magnetic truncation of the disk around a rapidly rotating T Tauri star is initially exterior to the corotation radius and “propeller” accretion is accompanied by an inner magnetized wind, shielding the disk from X-rays. Because rotation varies little due to angular momentum exchange with the disk, stellar contraction causes the truncation radius to migrate inside the corotation radius, the inner wind to disappear, and photoevaporation to erode a gap in the disk, accelerating its dissipation. This X-ray attenuation scenario explains the trend of the longer lifetime, reduced structure, and compact size of disks around lower-mass stars. It also explains an observed lower bound and scatter in the distribution of disk accretion rates. Disks that experience early photoevaporation and form gaps can efficiently trap solids at a pressure bump at 1–10 au, triggering giant planet formation, while those with later-forming gaps or indeed no gaps form multiple smaller planets on close-in orbits, a pattern that is consistent with observed exoplanet demographics.
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- Award ID(s):
- 2106927
- PAR ID:
- 10633279
- Publisher / Repository:
- EDP Sciences
- Date Published:
- Journal Name:
- Astronomy astrophysics
- Volume:
- 696
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A207
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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