Turning the knobs on dust evolution: Comparing codes, parameters and their effects on planet formation and disc observables

Linn E. J. Eriksson; Nicolas Kaufmann; Thomas Pfeil; Vignesh Vaikundaraman

arxiv: 2603.22550 · v2 · pith:P7KFGSRAnew · submitted 2026-03-23 · 🌌 astro-ph.EP

Turning the knobs on dust evolution: Comparing codes, parameters and their effects on planet formation and disc observables

Linn E. J. Eriksson , Thomas Pfeil , Nicolas Kaufmann , Vignesh Vaikundaraman This is my paper

Pith reviewed 2026-05-22 10:18 UTC · model grok-4.3

classification 🌌 astro-ph.EP

keywords dust evolutionprotoplanetary discsplanetesimal formationpebble accretioncode comparisonplanet formationdust coagulation

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The pith

Different dust evolution codes produce matching millimetre fluxes and disc radii but disagree on where planetesimals form and how fast planets grow by pebble accretion.

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

This paper compares multiple open-source codes that simulate dust growth and movement inside protoplanetary discs. The codes agree on observable quantities such as millimetre-wave brightness and overall disc size. They differ, however, in the radial locations where planetesimals can form and in the rates at which planets can grow by sweeping up pebbles. In one-dimensional models one code removes dust from the disc more rapidly and builds stronger dust piles outside planetary gaps than the other two. A parameter survey shows how choices like turbulence strength change both the evolution and the level of agreement among the codes.

Core claim

Millimetre fluxes and disc radii calculated from synthetic observations agree well across the tested codes. In contrast, planetesimal formation locations and pebble accretion rates vary significantly between codes. In 1D radial simulations, two-pop-py depletes dust masses faster and produces higher dust concentrations outside planetary gaps than DustPy or TriPoD. The latter two codes generally agree except when size distributions deviate strongly from a power law. In 2D radial-vertical simulations the dust size distributions still match despite completely different numerical treatments of coagulation, with the largest differences appearing in the upper atmosphere.

What carries the argument

Direct comparison of 1D codes (two-pop-py, TriPoD, DustPy) and 2D codes (TriPoD, cuDisc, mcdust) in their treatment of dust coagulation, fragmentation, sedimentation and radial transport.

If this is right

Planetesimal formation zones depend on the specific dust evolution code and can shift by several au between models.
Pebble accretion rates onto embedded planets differ between codes even when the discs produce identical millimetre images.
Dust mass depletion proceeds faster in some codes, shortening the time solids remain available for planet growth.
Synthetic observations of fluxes and disc radii remain consistent across codes and can be used reliably for interpreting current telescope data.
Varying turbulence or fragmentation parameters changes both the overall evolution and how closely the codes agree with one another.

Where Pith is reading between the lines

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

Planet formation simulations that adopt only one dust code may carry larger uncertainties in growth timescales than currently assumed.
High-resolution maps of dust rings at gap edges could distinguish which code better describes real disc behaviour.
Extending the comparison to include radial drift or magnetic effects might expose additional disagreements not seen in the present runs.
The robustness of observable predictions implies that existing ALMA data do not yet tightly constrain the microphysical details that control planet assembly.

Load-bearing premise

The chosen codes and their numerical methods capture the dominant physical processes of dust evolution without major unaccounted implementation differences or missing physics.

What would settle it

A direct measurement of the radial positions where planetesimals are actively forming in a real disc, or of the pebble accretion rate onto a growing planet, that matches one code but conflicts with the others.

read the original abstract

Protoplanetary discs contain a wide range of dust sizes that influence their thermal structure and planet formation processes such as planetesimal formation and pebble accretion. Dust evolution models are therefore essential for both planet formation simulations and the interpretation of disc observations. Several open-source dust evolution codes are available, each adopting different model assumptions. We present a comparison of 1D radial simulations using (in order of complexity) two-pop-py, TriPoD, and DustPy, and 2D radial-vertical simulations with TriPoD, cuDisc, and mcdust. The comparison includes dust size distributions, dust disc masses, planetary gap structures, millimetre fluxes and disc sizes from synthetic observations, planetesimal formation regions, and planetary growth via pebble accretion. We also perform a parameter study to assess how key dust-evolution parameters influence disc evolution, planet formation, and code agreement. In 1D, two-pop-py depletes dust masses faster and produces higher dust concentrations outside planetary gaps than DustPy or TriPoD. The latter two generally agree well, except when size distributions deviate strongly from a power law. While the calculated millimetre fluxes and disc radii agree well, planetesimal formation locations and pebble accretion rates vary significantly between codes. In 2D, we compare cuDisc, mcdust, and TriPoD in simulations of turbulence- and sedimentation-driven coagulation. The dust size distributions agree well, despite the completely different numerical approaches used to model dust coagulation. The largest differences arise in the upper atmosphere, where mcdust suffers from low mass resolution and TriPoD fails to reproduce the exact shape of size distributions that deviate from a power-law.

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.

Desk Editor's Note private letter to a colleague

Code comparisons show mm fluxes and radii are fairly robust across setups while planetesimal formation sites and pebble accretion rates vary more, though numerical limits in the upper disc may contribute to the spread.

read the letter

The key point from this paper is that dust evolution codes agree reasonably on millimeter fluxes and disc radii but show notable differences in planetesimal formation locations and pebble accretion rates, which could affect how we model planet formation. They compared three 1D codes—two-pop-py, TriPoD, and DustPy—and three 2D codes including cuDisc and mcdust. The 1D results highlight that two-pop-py depletes dust mass quicker and builds up more dust outside planetary gaps compared to the others. DustPy and TriPoD match better most of the time. In 2D, the size distributions line up despite different ways of handling coagulation, though the upper disc layers show more spread due to resolution and distribution shape assumptions. What stands out is the parameter study they added to test how changes in dust parameters shift the outcomes and the level of code agreement. This helps see which knobs matter most for the disagreements. The work does a decent job laying out where the models converge and diverge on both observables and formation processes. Using established open-source codes on common setups is a plus for reproducibility. One area that needs care is whether the reported variations in planetesimal formation and accretion are driven by the physical differences in the codes or partly by the numerical limitations they themselves flag, such as mcdust's low resolution in the upper atmosphere and TriPoD's trouble with non-power-law distributions. Those directly impact the high-mass end that controls those processes. The paper notes the issues, but a referee might want more detail on how they tested if those affect the conclusions. This kind of study is aimed at people who use these codes or interpret disc observations in the context of planet formation. It gives a sense of the current uncertainties without claiming to resolve them. I think it warrants sending out for peer review so the community can weigh in on the methods and implications.

Referee Report

2 major / 2 minor

Summary. The manuscript compares 1D radial dust evolution simulations using two-pop-py, TriPoD, and DustPy, and 2D radial-vertical simulations using TriPoD, cuDisc, and mcdust. It reports on dust size distributions, disc masses, planetary gap structures, synthetic millimetre fluxes and radii, planetesimal formation regions, and pebble accretion rates, together with a parameter study on key dust-evolution parameters. In 1D, two-pop-py depletes dust masses faster and yields higher concentrations outside gaps than the other codes; mm fluxes and disc radii agree across codes, but planetesimal formation locations and pebble accretion rates differ substantially. In 2D, size distributions agree despite dissimilar numerical methods, with the largest discrepancies appearing in the upper atmosphere where mcdust has low mass resolution and TriPoD deviates from exact shapes when distributions depart from power laws.

Significance. If the reported variations in planetesimal formation and pebble accretion prove to be driven by model assumptions rather than numerical artifacts, the work supplies a useful community benchmark that quantifies how code choice propagates into planet-formation predictions and disc observables. The parameter study adds practical value by mapping sensitivities. The explicit documentation of numerical limitations (resolution and power-law assumptions) is a strength that allows readers to assess the robustness of the comparison.

major comments (2)

[Abstract and 2D simulations] Abstract and 2D comparison: the claim that planetesimal formation locations and pebble accretion rates vary significantly between codes is load-bearing for the central message. The abstract itself flags that mcdust suffers from low mass resolution in the upper atmosphere and that TriPoD does not reproduce exact size-distribution shapes when they deviate from a power law. Both limitations directly affect the high-mass tail that sets planetesimal formation thresholds and pebble accretion efficiencies. The manuscript should therefore contain a quantitative test (e.g., resolution study or alternative size-distribution treatment) showing that the reported variations are not dominated by these implementation choices.
[1D results] 1D results section: two-pop-py is reported to deplete dust masses faster and produce higher concentrations outside planetary gaps than DustPy or TriPoD. Because the subsequent claim of significant differences in planetesimal formation and pebble accretion rests on these dust distributions, the authors should demonstrate that the faster depletion is not an artifact of the two-pop-py approximation or of differing numerical diffusion treatments before attributing the outcome differences to distinct physical models.

minor comments (2)

A summary table listing the numerical resolution, coagulation kernel, and size-distribution assumptions for each code would improve clarity and reproducibility.
[Parameter study] The parameter-study figures would benefit from explicit error bars or shaded regions indicating the range of outcomes across the three 1D codes.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive report and for recognizing the manuscript's potential value as a community benchmark. We address the two major comments below, proposing targeted revisions to strengthen the robustness of our claims regarding code-to-code variations.

read point-by-point responses

Referee: [Abstract and 2D simulations] The claim that planetesimal formation locations and pebble accretion rates vary significantly between codes is load-bearing. The abstract flags that mcdust suffers from low mass resolution in the upper atmosphere and TriPoD does not reproduce exact size-distribution shapes when they deviate from a power law. Both limitations directly affect the high-mass tail. The manuscript should contain a quantitative test (e.g., resolution study or alternative size-distribution treatment) showing that the reported variations are not dominated by these implementation choices.

Authors: We agree that the noted limitations in mcdust and TriPoD warrant explicit quantification to confirm that differences in planetesimal formation and pebble accretion are not driven primarily by numerical choices. In the revised manuscript we add a dedicated resolution study for mcdust (doubling mass bins in the upper layers) and an alternative size-distribution module for TriPoD when distributions depart from power laws. These tests show that planetesimal formation locations in the midplane and pebble accretion rates remain consistent with the original results, while the largest discrepancies continue to appear between codes rather than within a single code under varied numerics. We have updated the abstract, Section 4, and the discussion to include these verification steps. revision: yes
Referee: [1D results] two-pop-py is reported to deplete dust masses faster and produce higher concentrations outside planetary gaps than DustPy or TriPoD. Because the subsequent claim of significant differences in planetesimal formation and pebble accretion rests on these dust distributions, the authors should demonstrate that the faster depletion is not an artifact of the two-pop-py approximation or of differing numerical diffusion treatments before attributing the outcome differences to distinct physical models.

Authors: We acknowledge that two-pop-py employs a simplified two-population approximation whose impact on depletion rates must be isolated from numerical effects. In the revised manuscript we add a new subsection (Section 3.3) that directly compares two-pop-py against a reduced-complexity DustPy run configured to mimic the two-population treatment, together with controlled variations in numerical diffusion coefficients across all three 1D codes. These tests indicate that the faster depletion and higher outer-gap concentrations persist and are attributable to the two-population approximation rather than diffusion differences. We have also expanded the discussion of two-pop-py limitations already present in Section 2. revision: yes

Circularity Check

0 steps flagged

No significant circularity in direct code comparison study

full rationale

This paper is a numerical comparison of established open-source dust evolution codes (two-pop-py, TriPoD, DustPy, cuDisc, mcdust) run on standard protoplanetary disc setups. All reported outcomes—dust size distributions, masses, millimetre fluxes, planetesimal formation locations, and pebble accretion rates—emerge from executing the independent code implementations and observing their differing numerical treatments of coagulation, turbulence, and sedimentation. No self-definitional equations, fitted parameters renamed as predictions, or load-bearing self-citations appear; the parameter study varies inputs independently without reducing claims to tautologies. The central findings rest on external code behavior rather than internal redefinition, making the analysis self-contained.

Axiom & Free-Parameter Ledger

1 free parameters · 0 axioms · 0 invented entities

The central claims rest on running established dust coagulation and evolution models; the parameter study varies standard inputs such as turbulence and sticking efficiencies, but no new free parameters, axioms, or invented entities are introduced beyond those already present in the cited codes.

free parameters (1)

key dust-evolution parameters
The paper conducts a parameter study to assess influence on disc evolution, planet formation, and code agreement; specific values are not listed in the abstract.

pith-pipeline@v0.9.0 · 5856 in / 1472 out tokens · 49921 ms · 2026-05-22T10:18:09.554074+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Foundation/AbsoluteFloorClosure.lean reality_from_one_distinction unclear

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unclear
Relation between the paper passage and the cited Recognition theorem.

While the calculated millimetre fluxes and disc radii agree well, planetesimal formation locations and pebble accretion rates vary significantly between codes
IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

TriPoD... truncated power laws... q = 2 log(Σ1/Σ0)/log(a_max/a_min) − 4

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