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arxiv: 2603.07711 · v1 · submitted 2026-03-08 · 🌌 astro-ph.EP

Dust distribution in circumstellar disks harboring multi-planet systems. II. Super-thermal mass planets

V. Roatti , G. Picogna , F. Marzari This is my paper

Pith reviewed 2026-05-15 14:49 UTC · model grok-4.3

classification 🌌 astro-ph.EP
keywords circumstellar disksdust distributionmulti-planet systemshydrodynamical simulationsALMA observationsplanetary perturbationsgrain growthsecular effects
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The pith

Multi-planet systems produce dust morphologies that cannot be described as a simple superposition of single-planet gaps.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper performs two-dimensional hydrodynamical simulations of circumstellar disks containing two super-thermal mass planets to examine the resulting dust distribution across a range of particle sizes. It shows that secular perturbations between the planets create multiple dust traps, asymmetric structures, and eccentric particle orbits whose locations and widths vary with particle size, planet mass, and orbital separation. These effects mean that synthetic ALMA continuum images can hide the gaps carved by multiple planets, complicating efforts to infer planetary properties from observed substructures. Eccentric orbits also increase relative velocities between grains and strengthen gas drag, which reduces effective Stokes numbers and favors fragmentation over further grain growth.

Core claim

Dust morphologies in multi-planet systems cannot be described as a simple superposition of single-planet gaps. Secular planetary perturbations can generate multiple dust traps and asymmetric structures, while also exciting significant eccentricities in dust particle orbits. As a consequence, the locations and widths of dust rings and gaps depend on the size of the particles, the masses of the planet, and the orbital configurations. Synthetic continuum images may hide gaps carved by multiple planets, thereby complicating the interpretation of observed substructures. In addition, eccentricities induced in dust orbits lead to stronger gas drag, reducing the Stokes number for a given particle大小,

What carries the argument

Two-dimensional hydrodynamical simulations treating dust as Lagrangian particles of varying sizes, with post-processing via radiative transfer to generate synthetic ALMA continuum maps.

If this is right

  • Ring and gap locations and widths vary with dust particle size, planet masses, and orbital configurations.
  • Synthetic images can mask the presence of multiple planets and their individual gaps.
  • Eccentric dust orbits increase gas drag and lower the effective Stokes number for a given particle size.
  • Higher relative velocities from eccentric orbits favor grain fragmentation and replenish small dust.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Interpreting ALMA disk substructures to infer planet masses may require models that include multi-planet secular effects rather than single-planet templates.
  • Multi-wavelength imaging could directly test the predicted size-dependent trapping by comparing ring positions across bands.
  • Suppressed grain growth in such systems could slow the supply of larger solids available for planetesimal formation.
  • Similar complex dust patterns may appear in systems with three or more planets or different mass ratios.

Load-bearing premise

Two-dimensional hydrodynamical simulations treating dust as Lagrangian particles without coagulation or full three-dimensional vertical dynamics accurately represent real circumstellar disk processes and observational signatures.

What would settle it

Multi-wavelength ALMA observations of a disk known to contain multiple giant planets that show dust ring locations and widths independent of observing wavelength rather than the size-dependent shifts predicted by the simulations.

Figures

Figures reproduced from arXiv: 2603.07711 by F. Marzari, G. Picogna, V. Roatti.

Figure 1
Figure 1. Figure 1: The formation of multiple dust traps by a single planet [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 1
Figure 1. Figure 1: Dust distributions for three representative grain sizes. From left to right: 100 µm, 1.6 mm, and 2.6 cm particles. Rows correspond to different planetary configurations: single planet (top), two Jupiter-mass planets on close orbits (second), two Jupiter-mass planets on wide orbits (third), and a Jupiter–Saturn pair on wide orbits (bottom). The black dashed curve shows the radial gas surface density profile… view at source ↗
Figure 2
Figure 2. Figure 2: Radial distribution of dust particle number density for each model, computed in radial bins of 0.25 au. Black, red, and blue lines correspond to 100 µm, 1.6 mm, and 2.6 cm particles, respectively. Orange filled circles mark the planet locations. Top left: single planet. Top right: two Jupiter-mass planets on close orbits. Bottom panels: wide-orbit configurations. planet, thereby preventing the formation of… view at source ↗
Figure 3
Figure 3. Figure 3: Dust particle orbital eccentricity versus radial distance for each model. Green filled circles mark planet locations. Colored points denote grain sizes of 100 µm (green), 1.6 mm (cyan), and 2.6 cm (magenta). ever, the pebble distribution is significantly different. In the case of close planets, a dense ring forms within 5 au, inside the orbit of the inner planet, whereas for two distant planets, the dense … view at source ↗
Figure 4
Figure 4. Figure 4: Gas and dust distributions for two widely separated Jupiter-mass planets. Blue dots represent 1.6-mm dust particles, superimposed on the perturbed gas surface density ∆Σ/Σ0 (color scale). Green (yellow) dashed lines indicate the 2:1 (3:2) mean motion resonance with the outer planet. The plot is zoomed in the region between 15 to 35 AU to better visualize the dust overdensity near the outer gap edge. number… view at source ↗
Figure 5
Figure 5. Figure 5: Dust continuum emission convolved with a realistic ALMA beam in Band 7 (first row), Band 6 (second row) and Band 3 (third row). Columns correspond to the models CloseJup (left), WideJup (middle), and WideSat (right). Bottom panel: radial intensity profiles in Bands 7 (brown), 6 (orange), and 3 (yellow), together with dust (blue dashed) and gas (black dashed) radial profiles. Cyan crosses and green filled c… view at source ↗
Figure 6
Figure 6. Figure 6: Mean impact velocities between dust grains of the same size as a function of radial distance. Top: two Jupiter-mass planets on close orbits. Middle: two widely separated Jupiter-mass planets. Bottom: Jupiter–Saturn pair. masses and orbital configurations, providing a more detailed view of the 2D dust distribution and kinematics for different grain sizes; – Dust particles experience enhanced relative veloci… view at source ↗
read the original abstract

Theoretical formation models and exoplanet detection surveys indicate that systems with multiple giant planets are common. We investigate how multiple super-thermal mass planets embedded in a circumstellar disk shape the dust distribution and examine the consequences for interpreting disk substructures and inferring planetary properties. We perform two-dimensional hydrodynamical simulations with a modified PLUTO code, treating dust as Lagrangian particles in a wide range of sizes. We analyze systems with two planets of different masses and orbital separations, comparing them to the single-planet scenario. We generate synthetic ALMA continuum maps using RADMC-3D and compute the relative impact velocities of dust particles to assess potential limitations to grain growth. Dust morphologies in multi-planet systems cannot be described as a simple superposition of single-planet gaps. Secular planetary perturbations can generate multiple dust traps and asymmetric structures, while also exciting significant eccentricities in dust particle orbits. As a consequence, the locations and widths of dust rings and gaps depend on the size of the particles, the masses of the planet, and the orbital configurations. Synthetic continuum images may hide gaps carved by multiple planets, thereby complicating the interpretation of observed substructures. In addition, eccentricities induced in dust orbits lead to stronger gas drag, reducing the Stokes number for a given particle size, and the enhanced relative velocities associated with eccentric orbits can further suppress grain growth, promoting fragmentation and replenishment of small dust grains.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper claims that dust morphologies in circumstellar disks with multiple super-thermal mass planets cannot be modeled as a simple superposition of single-planet gaps. Using 2D hydrodynamical simulations with a modified PLUTO code and Lagrangian dust particles of varying sizes, it shows that secular planetary perturbations generate multiple dust traps, asymmetric structures, and size-dependent eccentricities in dust orbits. These effects make ring/gap locations and widths dependent on particle size, planet masses, and orbital configurations. Synthetic ALMA continuum maps via RADMC-3D are used to illustrate observational complications, and relative dust velocities are computed to assess impacts on grain growth.

Significance. If the central results hold, the work is significant for interpreting ALMA observations of disk substructures in multi-planet systems, which formation models suggest are common. It provides direct numerical evidence that secular effects produce complex, non-superposable dust features including multiple traps and eccentric orbits, with consequences for inferring planet properties from gaps and rings. Strengths include explicit comparisons to single-planet cases and generation of synthetic images; the direct simulation approach avoids circular parameter fitting.

major comments (2)
  1. [Methods] Methods section: the hydrodynamical setup provides no grid resolution, time-step criteria, or convergence tests for the PLUTO runs, which is load-bearing for the reported secular perturbations, multiple dust traps, and excited eccentricities; without these, it is unclear whether the non-superposition result is robust.
  2. [Results] Results and Discussion: the central claim that secular perturbations produce multiple traps and significant eccentricities (preventing simple superposition) is derived entirely from 2D simulations; the manuscript does not address how vertical dust settling, midplane concentration, or 3D vertical shear—omitted here—might damp eccentricities or merge traps, weakening the conclusion if 3D effects alter the reported morphologies.
minor comments (2)
  1. [Introduction] Abstract and introduction: the paper is labeled 'II' but does not briefly summarize the scope of part I or how the super-thermal mass regime extends prior single-planet results.
  2. [Figures] Figure captions: ensure synthetic ALMA maps explicitly mark planet locations, masses, and orbital separations to facilitate direct visual comparison with the single-planet reference cases.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive and detailed review of our manuscript. We have addressed both major comments by expanding the Methods section with the requested numerical details and by adding a discussion of the limitations of the 2D approach in the Results and Discussion sections. The revisions strengthen the presentation without altering the core conclusions.

read point-by-point responses

  1. Referee: [Methods] Methods section: the hydrodynamical setup provides no grid resolution, time-step criteria, or convergence tests for the PLUTO runs, which is load-bearing for the reported secular perturbations, multiple dust traps, and excited eccentricities; without these, it is unclear whether the non-superposition result is robust.

    Authors: We agree that explicit documentation of the numerical parameters is necessary to demonstrate robustness. In the revised manuscript we have added a new subsection to the Methods that specifies the grid resolution (512 radial by 1024 azimuthal cells for the fiducial runs), the CFL time-step criterion employed by PLUTO, and the results of convergence tests performed at doubled resolution. These tests show that the locations and number of dust traps, the amplitude of secular eccentricity excitation, and the overall non-superposable morphology remain unchanged, confirming that the reported effects are not resolution-dependent. revision: yes

  2. Referee: [Results] Results and Discussion: the central claim that secular perturbations produce multiple traps and significant eccentricities (preventing simple superposition) is derived entirely from 2D simulations; the manuscript does not address how vertical dust settling, midplane concentration, or 3D vertical shear—omitted here—might damp eccentricities or merge traps, weakening the conclusion if 3D effects alter the reported morphologies.

    Authors: We acknowledge that our simulations are strictly two-dimensional and therefore omit vertical structure. In the revised manuscript we have inserted a dedicated paragraph in the Discussion that addresses this limitation. We note that vertical settling concentrates dust toward the midplane, where the 2D dynamics remain a good approximation, and that the secular planetary perturbations operate on orbital timescales that are largely unaffected by vertical shear for the particle sizes considered. While full 3D simulations would be required to quantify any damping or merging of traps, the in-plane secular effects we report are expected to persist and set a baseline for the complexity of dust distributions in multi-planet systems. We have therefore framed our conclusions as applying to the midplane dust layer while explicitly calling for future 3D work. revision: partial

Circularity Check

0 steps flagged

No significant circularity; results from direct hydrodynamical simulations

full rationale

The paper's central claims rest on two-dimensional hydrodynamical simulations performed with a modified PLUTO code, in which dust is treated as Lagrangian particles across a range of sizes. Multi-planet configurations are explicitly compared to single-planet reference runs, with post-processing via RADMC-3D for synthetic ALMA maps and direct computation of particle relative velocities. No analytical derivation chain, parameter fitting followed by prediction of related quantities, or self-definitional relations appear; the reported non-superposition morphologies, multiple traps, and eccentricity excitation emerge from the simulation outputs themselves rather than by construction. Any self-citations to prior work (e.g., part I of the series) are not load-bearing for the multi-planet results presented here.

Axiom & Free-Parameter Ledger

3 free parameters · 2 axioms · 0 invented entities

The central claims rest on numerical hydrodynamical simulations whose outcomes depend on chosen planet masses, separations, disk viscosity, and dust size distributions, plus standard assumptions about 2D gas-dust coupling.

free parameters (3)
  • Planet masses and orbital separations
    Selected to represent super-thermal mass planets in varied configurations for comparison to single-planet cases.
  • Dust particle size distribution
    Wide range simulated to demonstrate size-dependent trap locations and eccentricities.
  • Disk viscosity and surface density profile
    Standard but unspecified parameters that control gap opening and dust trapping.
axioms (2)
  • domain assumption Two-dimensional hydrodynamical equations with Lagrangian dust particles capture the dominant dynamics
    Core modeling choice in the modified PLUTO code.
  • domain assumption Dust does not coagulate or fragment during the simulation; only relative velocities are computed post hoc
    Used to assess limits on grain growth.

pith-pipeline@v0.9.0 · 5564 in / 1613 out tokens · 42600 ms · 2026-05-15T14:49:38.791391+00:00 · methodology

discussion (0)

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Works this paper leans on

46 extracted references · 46 canonical work pages

  1. [1]

    L., Pérez, L

    ALMA Partnership, Brogan, C. L., Pérez, L. M., et al. 2015, ApJ, 808, L3

    work page 2015

  2. [2]

    M., Huang, J., Pérez, L

    Andrews, S. M., Huang, J., Pérez, L. M., et al. 2018, ApJ, 869, L41

    work page 2018

  3. [3]

    Armitage, P. J. 2020, Astrophysics of planet formation, Second Edition (Cam- bridge University Press)

    work page 2020

  4. [4]

    P., Garufi, A., et al

    Avenhaus, H., Quanz, S. P., Garufi, A., et al. 2018, ApJ, 863, 44

    work page 2018

  5. [5]

    2019, MNRAS, 486, 304 Bernabò, L

    Baruteau, C., Barraza, M., Pérez, S., et al. 2019, MNRAS, 486, 304 Bernabò, L. M., Turrini, D., Testi, L., Marzari, F., & Polychroni, D. 2022, ApJ, 927, L22

    work page 2019

  6. [6]

    2024, ARA&A, 62, 157

    Birnstiel, T. 2024, ARA&A, 62, 157

    work page 2024

  7. [7]

    2018, A&A, 612, A30

    Bitsch, B., Morbidelli, A., Johansen, A., et al. 2018, A&A, 612, A30

    work page 2018

  8. [8]

    2011, ApJ, 737, 33

    Charnoz, S., Fouchet, L., Aleon, J., & Moreira, M. 2011, ApJ, 737, 33

    work page 2011

  9. [9]

    J., Ziampras, A., Brown, J

    Cordwell, A. J., Ziampras, A., Brown, J. J., & Rafikov, R. R. 2025, MNRAS, 543, 4198

    work page 2025

  10. [10]

    2006, Icarus, 181, 587 de Val-Borro, M., Edgar, R

    Crida, A., Morbidelli, A., & Masset, F. 2006, Icarus, 181, 587 de Val-Borro, M., Edgar, R. G., Artymowicz, P., et al. 2006, MNRAS, 370, 529

    work page 2006

  11. [11]

    2021, OpTool: Command-line driven tool for creating complex dust opacities, Astrophysics Source Code Library, record ascl:2104.010

    Dominik, C., Min, M., & Tazaki, R. 2021, OpTool: Command-line driven tool for creating complex dust opacities, Astrophysics Source Code Library, record ascl:2104.010

    work page 2021

  12. [12]

    & Fung, J

    Dong, R. & Fung, J. 2017, ApJ, 835, 146

    work page 2017

  13. [13]

    2018, ApJ, 866, 110

    Dong, R., Li, S., Chiang, E., & Li, H. 2018, ApJ, 866, 110

    work page 2018

  14. [14]

    Draine, B. T. 2003, ARA&A, 41, 241 Dr˛ a˙ zkowska, J. & Alibert, Y . 2017, A&A, 608, A92

    work page 2003

  15. [15]

    P., Juhasz, A., Pohl, A., et al

    Dullemond, C. P., Juhasz, A., Pohl, A., et al. 2012, RADMC-3D: A multi- purpose radiative transfer tool, Astrophysics Source Code Library, record ascl:1202.015

    work page 2012

  16. [16]

    J., Klahr, H., & Henning, T

    Dzyurkevich, N., Flock, M., Turner, N. J., Klahr, H., & Henning, T. 2010, A&A, 515, A70

    work page 2010

  17. [17]

    P., Dzyurkevich, N., et al

    Flock, M., Ruge, J. P., Dzyurkevich, N., et al. 2015, A&A, 574, A68 Gárate, M., Birnstiel, T., Dr˛ a˙ zkowska, J., & Stammler, S. M. 2020, A&A, 635, A149

    work page 2015

  18. [18]

    Ida, S., Lin, D. N. C., & Nagasawa, M. 2013, ApJ, 775, 42

    work page 2013

  19. [19]

    2016, Phys

    Isella, A., Guidi, G., Testi, L., et al. 2016, Phys. Rev. Lett., 117, 251101

    work page 2016

  20. [20]

    M., et al

    Isella, A., Huang, J., Andrews, S. M., et al. 2018, ApJ, 869, L49

    work page 2018

  21. [21]

    A., Fulton, B

    Knutson, H. A., Fulton, B. J., Montet, B. T., et al. 2014, ApJ, 785, 126

    work page 2014

  22. [22]

    2014, A&A, 572, A35

    Lambrechts, M., Johansen, A., & Morbidelli, A. 2014, A&A, 572, A35

    work page 2014

  23. [23]

    Lin, D. N. C. & Papaloizou, J. 1986, ApJ, 307, 395

    work page 1986

  24. [24]

    Lissauer, J. J. & Stewart, G. R. 1993, in Protostars and Planets III, ed. E. H. Levy & J. I. Lunine, 1061

    work page 1993

  25. [25]

    2009, A&A, 493, 1125

    Lyra, W., Johansen, A., Klahr, H., & Piskunov, N. 2009, A&A, 493, 1125

    work page 2009

  26. [26]

    2019, AJ, 157, 45

    Marzari, F., D’Angelo, G., & Picogna, G. 2019, AJ, 157, 45

    work page 2019

  27. [27]

    2021, A&A, 650, A116

    Matsumura, S., Brasser, R., & Ida, S. 2021, A&A, 650, A116

    work page 2021

  28. [28]

    2007, ApJS, 170, 228 Müller, T

    Mignone, A., Bodo, G., Massaglia, S., et al. 2007, ApJS, 170, 228 Müller, T. W. A., Kley, W., & Meru, F. 2012, A&A, 541, A123

    work page 2007

  29. [29]

    B., Millán, E

    Parizek, F., Planes, M. B., Millán, E. N., Parisi, M. G., & Bringa, E. M. 2025, A&A, 703, A180

    work page 2025

  30. [30]

    Picogna, G., Stoll, M. H. R., & Kley, W. 2018, A&A, 616, A116

    work page 2018

  31. [31]

    2012, A&A, 545, A81

    Pinilla, P., Benisty, M., & Birnstiel, T. 2012, A&A, 545, A81

    work page 2012

  32. [32]

    2015, A&A, 573, A9

    Pinilla, P., de Juan Ovelar, M., Ataiee, S., et al. 2015, A&A, 573, A9

    work page 2015

  33. [33]

    & Lesur, G

    Riols, A. & Lesur, G. 2019, A&A, 625, A108

    work page 2019

  34. [34]

    2025, A&A, 703, A270

    Roatti, V ., Picogna, G., & Marzari, F. 2025, A&A, 703, A270

    work page 2025

  35. [35]

    P., Teague, R., Dullemond, C., Booth, R

    Rosotti, G. P., Teague, R., Dullemond, C., Booth, R. A., & Clarke, C. J. 2020, MNRAS, 495, 173

    work page 2020

  36. [36]

    P., & Armitage, P

    Ruzza, A., Lodato, G., Rosotti, G. P., & Armitage, P. J. 2025, A&A, 700, A190

    work page 2025

  37. [37]

    Shakura, N. I. & Sunyaev, R. A. 1973, A&A, 24, 337

    work page 1973

  38. [38]

    F., et al

    Testi, L., Natta, A., Manara, C. F., et al. 2022, A&A, 663, A98

    work page 2022

  39. [39]

    & Kley, W

    Thun, D. & Kley, W. 2018, A&A, 616, A47

    work page 2018

  40. [40]

    2019, ApJ, 877, 50

    Turrini, D., Marzari, F., Polychroni, D., & Testi, L. 2019, ApJ, 877, 50

    work page 2019

  41. [41]

    & Baruteau, C

    Wafflard-Fernandez, G. & Baruteau, C. 2020, MNRAS, 493, 5892

    work page 2020

  42. [42]

    Weidenschilling, S. J. 1977, MNRAS, 180, 57

    work page 1977

  43. [43]

    & Helling, C

    Woitke, P. & Helling, C. 2003, A&A, 399, 297

    work page 2003

  44. [44]

    Youdin, A. N. & Lithwick, Y . 2007, Icarus, 192, 588

    work page 2007

  45. [45]

    A., & Bergin, E

    Zhang, K., Blake, G. A., & Bergin, E. A. 2015, ApJ, 806, L7

    work page 2015

  46. [46]

    M., Rafikov, R

    Zhu, Z., Stone, J. M., Rafikov, R. R., & Bai, X.-n. 2014, ApJ, 785, 122 Article number, page 12 of 14 V . Roatti et al.: Dust distribution in circumstellar disks harboring multi-planet systems Appendix A: Dust continuum emission Figure A.1 shows the raw emission maps (before beam convolution) for the different multi-planet systems simulated in Band 7 (0.8...

    work page 2014