Turbulent disc viscosity and the bifurcation of planet formation histories
Bibliographic record
Abstract
ABSTRACT ALMA observations of dust ring/gap structures in a minority but growing sample of protoplanetary discs can be explained by the presence of planets at large disc radii – yet the origins of these planets remains debated. We perform planet formation simulations using a semi-analytic model of the HL Tau disc to follow the growth and migration of hundreds of planetary embryos initially distributed throughout the disc, assuming either a high or low turbulent α viscosity. We have discovered that there is a bifurcation in the migration history of forming planets as a consequence of varying the disc viscosity. In our high viscosity discs, inward migration prevails and yields compact planetary systems, tempered only by planet trapping at the water iceline around 5 au. In our lower viscosity models however, low mass planets can migrate outward to twice their initial orbital radii, driven by a radially extended region of strong outward-directed corotation torques located near the heat transition (where radiative heating of the disc by the star is comparable to viscous heating) – before eventually migrating inwards. We derive analytic expressions for the planet mass at which the corotation torque dominates, and find that this ‘corotation mass’ scales as Mp, corot ∼ α2/3. If disc winds dominate the corotation torque, the corotation mass scales linearly with wind strength. We propose that the observed bifurcation in disc demographics into a majority of compact dust discs and a minority of extended ring/gap systems is a consequence of a distribution of viscosity across the disc population.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".