arxiv: 2603.18337 · v1 · submitted 2026-03-18 · 🌌 astro-ph.EP

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Turbulence destroys thermal lobes around Mars-sized planetary embryos

R. O. Chametla , A. Moranchel-Basurto , F. J. S\'anchez-Salcedo

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Pith reviewed 2026-05-15 08:01 UTC · model grok-4.3

classification 🌌 astro-ph.EP

keywords planetary migrationprotoplanetary disksthermal torquesmagnetorotational instabilityturbulenceplanetary embryos

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The pith

Turbulence disrupts thermal lobes around Mars-sized planetary embryos, rendering thermal torques ineffective.

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

The paper examines how magnetorotational instability turbulence affects thermal lobes that form around a planetary embryo from its heat release in a protoplanetary disk. In quiet disks these lobes produce torques that can dominate over standard Lindblad and corotation effects. High-resolution 3D simulations with thermal diffusion and initial toroidal magnetic fields show that turbulence develops within 1.5 to 3 orbital periods and fully destroys the lobes for both low- and high-luminosity cases. The resulting torque on a 0.33 Mars-mass embryo and on a 1 Earth-mass core becomes strongly oscillatory. This outcome matters because it indicates that planets in the 0.03 to 1 Earth-mass range undergo stochastic rather than directed migration in turbulent disk regions outside dead zones.

Core claim

Even in the presence of a weak magnetic field and irrespective of luminosity, turbulence in the disk completely disrupts the thermal lobes around both the 0.33 Mars-mass embryo and the Earth-mass core, so that the torque on each object displays strongly oscillatory behavior.

What carries the argument

Thermal lobes produced by the embryo's heat release and thermal diffusion, which are destroyed by MRI-driven turbulence.

If this is right

The torque on the embryo and core becomes strongly oscillatory after turbulence develops.
Planets with masses 0.03 to 1 Earth mass undergo stochastic migration in turbulent disk regions.
Thermal torques are inefficient outside dead zones in both inner and outer disk regions.

Where Pith is reading between the lines

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

Smooth thermal-torque migration may be restricted to laminar dead zones.
Planet-formation models should treat migration in active disk zones as a random walk rather than a directed process.
Different initial magnetic-field geometries or longer simulation times could test whether lobes ever reform.

Load-bearing premise

The beta values of 50 and 1000 together with the initial toroidal field produce turbulence that is representative of realistic protoplanetary disk conditions outside dead zones.

What would settle it

High-resolution observations showing persistent thermal lobes inside known turbulent regions of a protoplanetary disk would falsify the claim of complete disruption.

Figures

Figures reproduced from arXiv: 2603.18337 by A. Moranchel-Basurto, F. J. S\'anchez-Salcedo, R. O. Chametla.

**Figure 3.** Figure 3: Quality factor averaged over space and time. The orange [PITH_FULL_IMAGE:figures/full_fig_p002_3.png] view at source ↗

**Figure 4.** Figure 4: Gas density (logarithmic scale) at the midplane at [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗

**Figure 5.** Figure 5: Temporal evolution of the total torque Γ (in units of Γ0/γ) on the planetary embryo. L = Lc 2 . Importantly, the torque behavior is largely insensitive to the value of β over this time interval (see the zoomed region in the right column of [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗

**Figure 6.** Figure 6: Temporal evolution of the total torque Γ (in units of Γ0/γ) on a planet of mass Mp = 1 M⊕, for β = 50 (blue lines) and β = 1000 (purple lines). stochastic for 0.03M⊕ ≲ Mp ≲ 1M⊕ as a result of MRI turbulence and for Mp ≳ 3M⊕ owing to vortices. Finally, we stress that the turn-off effect on the torque reported here is distinct from the cut-off effect investigated in Velasco Romero & Masset (2020). 4. Towa… view at source ↗

read the original abstract

The release of heat by a planetary embryo modifies the local density perturbations, forming thermal lobes in its vicinity, and thereby altering the torque exerted by the disk on the embryo. In laminar disks, these thermal torques can dominate the disk-embryo interaction, rendering the classical Lindblad and corotation torques largely subdominant. The aim of this work is to investigate how turbulence driven by the MRI instability affects the thermal lobes formed around a planetary embryo, and to analyze the resulting torque acting on the embryo. We evaluate the thermal torques exerted on a planetary embryo of mass $M_p=0.33M_{Mars}$ and on a planetary core with mass $M_{p}=1M_{\oplus}$, each embedded in a turbulent gaseous protoplanetary disk, by means of high-resolution 3D magnetohydrodynamics simulations that include thermal diffusion and an initially toroidal magnetic field. The magnetic field strength is characterized by the $\beta$-plasma parameter with $\beta\in\{50,1000\}$. We consider two values for the luminosity of the planetary embryo: $L=0$ (cold thermal lobes) and $L=L_c$ (hot thermal lobes), where $L_c$ represents the critical luminosity. We find that, even in the presence of a weak magnetic field and irrespective of the luminosity, for both planetary masses, the development of turbulence in the disk (which takes between 1.5 to 3 orbital periods) completely disrupts the thermal lobes. As a result, the torque acting on both the planetary embryo and the Earth-mass core displays a strongly oscillatory behavior. This suggests that planets with masses in the range $0.03M_{\oplus}\lesssim M_{p}\lesssim 1M_{\oplus}$ experience stochastic migration, as expected in turbulent disks. Thermal torques become inefficient in turbulent regions of protoplanetary disks, such as outside the dead zone, in both the inner and outer disk regions where the magnetorotational instability operates.

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

MRI turbulence disrupts thermal lobes in 1.5-3 orbits in these runs, shifting torques to oscillatory, but short durations leave open whether the effect persists long-term.

read the letter

The main result is that MRI-driven turbulence destroys the thermal lobes around both the Mars-mass embryo and the Earth-mass core within 1.5 to 3 orbital periods, regardless of luminosity or the two beta values tested. This turns the torque strongly oscillatory instead of the steady thermal torque seen in laminar disks. The paper shows this directly from the 3D MHD runs with thermal diffusion included. That is the new piece: prior thermal torque work stayed in laminar flows, and these simulations demonstrate how quickly the lobes vanish once turbulence sets in. The runs cover two masses, two betas, and both cold and hot cases, with consistent disruption and torque behavior across them. That gives the central claim decent support from the parameter sweeps. The soft spot is run length. The simulations end right around turbulence saturation, so it is not clear whether continuous heating plus diffusion would allow lobe reformation later or whether the oscillatory torque stays the dominant signal. That directly affects how far one can push the stochastic migration conclusion for 0.03-1 Earth-mass bodies. The beta and initial toroidal field choices are standard but still leave room to ask how representative they are of real disk conditions outside dead zones. This work is aimed at people modeling type-I migration in turbulent disks. The simulations are direct and the result is relevant enough that it deserves a serious referee, though longer runs and a bit more on convergence would strengthen it.

Referee Report

1 major / 2 minor

Summary. The paper uses high-resolution 3D MHD simulations with thermal diffusion to show that MRI-driven turbulence in protoplanetary disks (onset in 1.5–3 orbits) completely disrupts thermal lobes around both a 0.33 Mars-mass embryo and a 1 Earth-mass core. This holds for L=0 (cold lobes) and L=Lc (hot lobes) at beta=50 and 1000 with an initial toroidal field, replacing the dominant thermal torques of laminar disks with strongly oscillatory torques and implying stochastic migration for planets in the 0.03–1 M⊕ range outside dead zones.

Significance. If sustained, the result indicates that thermal torques are ineffective in MRI-active disk regions, altering migration prescriptions for low-mass embryos and cores. The direct numerical approach with multiple masses, beta values, and luminosities, plus explicit measurement of torque from evolved fields, provides a concrete test of laminar-disk assumptions and supports the shift to stochastic behavior in turbulent zones.

major comments (1)

[Results on torque evolution and density fields] The simulations are stopped near turbulence saturation (1.5–3 orbital periods after onset). This duration is insufficient to establish whether lobe disruption is permanent or transient, as continuous embryo heating plus thermal diffusion could allow reformation and damping of the oscillatory torque signal. This directly affects the central claim of persistent disruption and stochastic migration (see torque time series and density perturbation analysis).

minor comments (2)

[Methods] The critical luminosity Lc is referenced but its explicit definition and normalization (e.g., relative to disk properties) should be stated in the methods for reproducibility.
[Figures] Figure captions for density slices and torque plots should include the exact simulation times shown and the spatial scale in units of the Hill radius.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful and constructive review of our manuscript. We address the major comment below and have incorporated a partial revision to clarify the simulation limitations while defending the core findings on the basis of the rapid disruption observed.

read point-by-point responses

Referee: [Results on torque evolution and density fields] The simulations are stopped near turbulence saturation (1.5–3 orbital periods after onset). This duration is insufficient to establish whether lobe disruption is permanent or transient, as continuous embryo heating plus thermal diffusion could allow reformation and damping of the oscillatory torque signal. This directly affects the central claim of persistent disruption and stochastic migration (see torque time series and density perturbation analysis).

Authors: We agree that our simulations focus on the onset and initial saturation of MRI turbulence (1.5–3 orbits) and do not extend far into the long-term saturated state, which limits direct evidence for permanence versus possible later reformation. However, the density fields and torque time series demonstrate that thermal lobes are fully disrupted immediately upon turbulence development, with no reformation visible and torques becoming strongly oscillatory without damping in the simulated interval. This rapid transition supports the conclusion that thermal torques are rendered ineffective in MRI-active regions, leading to stochastic migration for the mass range considered. We have added a dedicated paragraph in the revised discussion section explicitly noting the finite simulation duration as a limitation and recommending longer integrations in future work to confirm persistence, while retaining the central claim based on the observed disruption mechanism. revision: partial

Circularity Check

0 steps flagged

No circularity: results are direct outputs of MHD simulations

full rationale

The paper reports outcomes from high-resolution 3D magnetohydrodynamic simulations with thermal diffusion and specified initial conditions (toroidal field, beta values 50 and 1000, luminosities L=0 and L=Lc). The central findings—that turbulence onset in 1.5–3 orbits disrupts thermal lobes and produces oscillatory torques—are measured quantities from the evolved density and velocity fields, not reductions of any fitted parameter or self-citation chain. No derivation steps exist that equate predictions to inputs by construction; the work is self-contained against external numerical benchmarks.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The claim rests on standard MHD equations plus thermal diffusion, with simulation parameters chosen to represent disk conditions. No new entities are postulated.

free parameters (2)

beta plasma parameter
Set to 50 and 1000 to characterize magnetic field strength; these control turbulence level.
planetary luminosity L
Set to 0 or critical value Lc to test cold vs hot lobes.

axioms (2)

standard math Standard ideal MHD equations with thermal diffusion govern the disk evolution.
Invoked throughout the simulation setup.
domain assumption Initial toroidal magnetic field and chosen beta values produce representative MRI turbulence.
Used to initialize the turbulent state.

pith-pipeline@v0.9.0 · 5681 in / 1310 out tokens · 52026 ms · 2026-05-15T08:01:32.795940+00:00 · methodology

discussion (0)

Reference graph

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