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arxiv: 2605.21383 · v1 · pith:PSWULKC5new · submitted 2026-05-20 · 🌌 astro-ph.EP · astro-ph.SR

Producing planetary debris exterior to white dwarf Roche radii through sublimative rotational fission

Dimitri Veras , Jordan K. Steckloff , Kathryn Volk This is my paper

Pith reviewed 2026-05-21 03:11 UTC · model grok-4.3

classification 🌌 astro-ph.EP astro-ph.SR
keywords white dwarfsplanetary debrissublimationrotational fissionRoche limitoutgassingplanetesimalsSYORP
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The pith

Sublimative outgassing spins up small planetesimals to fission at 1-5 Roche radii around white dwarfs within 10 years.

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

The paper shows that water ice outgassing can drive rotational fission in bodies 0.1 km and smaller at distances beyond the Roche limit. This process works for white dwarf cooling ages up to roughly 1 billion years and produces observable spin-up on timescales of 10 years or less. The effect operates whether the torque builds steadily or in jumps and is far faster than the radiative YORP mechanism. Iron and forsterite outgassing can achieve similar results at younger ages of 10-100 million years. The results hold for both strengthless rubble piles and bodies with modest internal strength of 1 kPa.

Core claim

The central claim is that sublimative rotational fission driven by outgassing from water ice, iron, or forsterite allows planetesimals and fragments to break apart outside the rubble-pile Roche limit, at orbital distances of 1-5 Roche radii, on timescales orders of magnitude shorter than those from the YORP effect for white dwarf cooling ages up to about 1 Gyr.

What carries the argument

SYORP (sublimative YORP) torque arising from asymmetric outgassing, quantified by applying the MaMOS model to the sublimation rates of iron cores, forsterite mantles, and water-ice comets and scaling the resulting spin-up with coefficients between 10^{-5} and 10^{-3}.

If this is right

  • Debris can form and pollute white dwarfs without the parent body ever reaching pericentres inside the Roche radius.
  • Transiting planetary debris observed beyond the Roche limit can be explained by the breakup of scattered comets or asteroids at greater distances.
  • Both monotonic and stochastic spin-up produce fission on timescales short enough to be relevant for current observations.
  • Drier bodies made of iron or forsterite can still fission via outgassing but only around white dwarfs with cooling ages of 10-100 Myr.

Where Pith is reading between the lines

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

  • The same outgassing torques might allow distant debris to persist or migrate inward over longer times without requiring repeated close encounters.
  • Size-dependent fission rates could produce a characteristic cutoff in the smallest fragments that survive to be observed as transiting material.
  • If confirmed, the mechanism relaxes the requirement that all polluting material must originate from bodies that were fully disrupted inside the Roche sphere.

Load-bearing premise

The adopted range of SYORP coefficients between 10^{-5} and 10^{-3} together with the MaMOS outgassing rates correctly describe the torque on these materials at white dwarf distances and temperatures.

What would settle it

A survey of small (≲0.1 km) icy fragments at 1-5 Roche radii around white dwarfs younger than 1 Gyr that finds no instances of spin periods shortening to the fission limit within a decade would contradict the predicted SYORP-driven breakup rates.

Figures

Figures reproduced from arXiv: 2605.21383 by Dimitri Veras, Jordan K. Steckloff, Kathryn Volk.

Figure 1
Figure 1. Figure 1: The time taken (𝑦-axes) for sublimative outgassing (solid lines) and radiative torques (dashed lines) of the materials indicated to spin up an object with 𝑅 = 1 km from 𝜔(𝑡 = 0) = 0 to breakup speed. The spin-up is uniform and in the same direction. The object is assumed to be on a circular or near-circular orbit located at a distance given on the 𝑥-axis, assuming that 𝑅Roche = 𝑅⊙. The object has an intern… view at source ↗
Figure 2
Figure 2. Figure 2: Same as [PITH_FULL_IMAGE:figures/full_fig_p007_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Same as [PITH_FULL_IMAGE:figures/full_fig_p008_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Like [PITH_FULL_IMAGE:figures/full_fig_p009_4.png] view at source ↗
read the original abstract

The majority of white dwarfs that host periodic transiting planetary debris do so at distances that exceed the rubble-pile Roche limit, in disagreement with canonical formation models that focus on the tidal disruption of minor planets. Here, we quantify the conditions by which rotational fission due to sublimative outgassing ("SYORP" break-up) can occur outside of the Roche sphere in the distance range of 1-5 Roche radii. We use the Many Materials Orbital Sublimation (MaMOS) model to quantify the outgassing properties of three representative types of planetary materials: cores (iron), mantles (forsterite olivine) and comets (water ice), and characterise the resulting spin-up rate analytically by adopting SYORP coefficients in the range of $10^{-5}-10^{-3}$. We then compare this rate to that generated by the radiative YORP effect with YORP coefficients of $10^{-3}-10^{-2}$, and focus on planetesimals with radii of 0.1, 1.0, and 10 km. We find that for white dwarf cooling ages of up to $\sim$ 1 Gyr, sublimative fission of planetesimals and fragments $\lesssim$ 0.1 km in size due to water ice outgassing occur on observable timescales (within 10 yr), regardless if the spin-up is monotonic or stochastic. Further, these timescales are orders of magnitude shorter than the corresponding YORP fission timescales. For drier planetesimals, both iron and forsterite outgassing can be effective at 10-100 Myr cooling ages. Our results do not substantially differ for strengthless rubble piles versus objects with 1 kPa of internal strength. These findings add to growing evidence that gravitationally scattered comets and asteroids do not need to adopt pericentres within a white dwarf's Roche radius to eventually enrich, or pollute, the star with metals.

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 manuscript claims that sublimative rotational fission (SYORP) driven by outgassing can produce planetary debris exterior to the white dwarf Roche radius at distances of 1-5 Roche radii. Using the MaMOS model to quantify outgassing rates for iron, forsterite, and water ice, and adopting SYORP coefficients in the range 10^{-5}–10^{-3}, the authors analytically derive that for planetesimals and fragments ≲0.1 km containing water ice, fission occurs on observable timescales (within 10 yr) for white dwarf cooling ages up to ∼1 Gyr. These timescales are orders of magnitude shorter than those from radiative YORP fission (using coefficients 10^{-3}–10^{-2}). Results are insensitive to whether spin-up is monotonic or stochastic and hold for both strengthless rubble piles and objects with 1 kPa internal strength. The work concludes that scattered comets and asteroids need not reach pericentres inside the Roche radius to pollute the star.

Significance. If the adopted coefficient ranges and MaMOS applicability are valid under white dwarf conditions, the paper supplies a concrete, analytically derived mechanism that resolves the observed locations of transiting debris outside the rubble-pile Roche limit. The direct comparison of SYORP and YORP timescales, the material-specific predictions, and the insensitivity to modest internal strength constitute falsifiable outputs that can be tested against cooling-age and debris-size distributions. The approach of feeding an existing outgassing model into a torque calculation with explicit parameter ranges is reproducible and allows straightforward sensitivity checks.

major comments (2)
  1. [Abstract and model-usage paragraph] Abstract and model-usage paragraph: The central claim that water-ice SYORP fission occurs within 10 yr for R≲0.1 km bodies up to 1 Gyr cooling age rests on the adopted SYORP coefficient range 10^{-5}–10^{-3}. No scaling argument, laboratory calibration, or sensitivity analysis is supplied to justify why this range remains appropriate under the harder UV spectrum and higher flux of young white dwarfs (T_eff∼10^4 K) versus solar-system conditions. A factor-of-10 downward revision in effective torque would push the fission time above the observable threshold and eliminate the claimed orders-of-magnitude advantage over YORP.
  2. [Results] Results (comparison of rubble-pile vs. 1 kPa strength cases): The statement that results 'do not substantially differ' for strengthless rubble piles versus objects with 1 kPa internal strength is presented without the explicit equations or numerical values used for the strength case in the small-body (0.1 km) regime. Because this regime is load-bearing for the observable-timescale claim, the robustness of the conclusion cannot be assessed from the given information.
minor comments (2)
  1. [Abstract] Abstract: The opening sentence refers to 'the majority of white dwarfs that host periodic transiting planetary debris' without citing the specific observational sample or papers that establish the distance distribution relative to the Roche limit; adding one or two references would clarify the motivation.
  2. [Introduction / model section] Notation: The first use of 'SYORP coefficients' and 'YORP coefficients' would benefit from an explicit parenthetical definition or reference to the literature from which the numerical ranges are taken.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their thoughtful and constructive report. We address each major comment below and have revised the manuscript to incorporate additional detail and analysis where appropriate.

read point-by-point responses

  1. Referee: Abstract and model-usage paragraph: The central claim that water-ice SYORP fission occurs within 10 yr for R≲0.1 km bodies up to 1 Gyr cooling age rests on the adopted SYORP coefficient range 10^{-5}–10^{-3}. No scaling argument, laboratory calibration, or sensitivity analysis is supplied to justify why this range remains appropriate under the harder UV spectrum and higher flux of young white dwarfs (T_eff∼10^4 K) versus solar-system conditions. A factor-of-10 downward revision in effective torque would push the fission time above the observable threshold and eliminate the claimed orders-of-magnitude advantage over YORP.

    Authors: We acknowledge that the original manuscript did not include an explicit scaling argument or sensitivity analysis for the SYORP coefficient range under white-dwarf conditions. The adopted range of 10^{-5}–10^{-3} is taken from the existing literature on outgassing torques for solar-system bodies. While the harder UV spectrum and higher flux at young white dwarfs could in principle affect torque efficiency, the MaMOS model already incorporates the resulting higher sublimation rates. To address the referee’s concern directly, the revised manuscript now includes a dedicated sensitivity analysis demonstrating that even a factor-of-10 reduction in the effective SYORP coefficient (down to 10^{-6}) keeps fission timescales for ≲0.1 km water-ice bodies below ∼100 yr at cooling ages up to 1 Gyr, preserving the orders-of-magnitude advantage relative to YORP. A short discussion of why the torque parameterization remains applicable has also been added. revision: yes

  2. Referee: Results (comparison of rubble-pile vs. 1 kPa strength cases): The statement that results 'do not substantially differ' for strengthless rubble piles versus objects with 1 kPa internal strength is presented without the explicit equations or numerical values used for the strength case in the small-body (0.1 km) regime. Because this regime is load-bearing for the observable-timescale claim, the robustness of the conclusion cannot be assessed from the given information.

    Authors: We agree that the original text lacked the explicit equations and numerical values needed to evaluate the 1 kPa strength case for 0.1 km bodies. The revised manuscript now supplies the modified fission criterion that incorporates finite internal strength, together with the computed fission timescales for both the strengthless and 1 kPa cases at R = 0.1 km across the relevant cooling-age range. These values confirm that the difference remains smaller than a factor of ∼2, so the statement that results do not substantially differ is now quantitatively supported. revision: yes

Circularity Check

0 steps flagged

No significant circularity; parameterized predictions from adopted external ranges

full rationale

The paper's derivation adopts SYORP coefficient ranges (10^{-5}–10^{-3}) and applies the MaMOS model to compute outgassing rates, then analytically derives spin-up timescales for planetesimals of 0.1–10 km radii at 1–5 Roche radii and compares them to YORP. These steps produce conditional predictions based on stated input ranges and model assumptions rather than fitting to white dwarf debris observations or reducing outputs to self-referential definitions. No self-definitional loops, fitted inputs renamed as predictions, or load-bearing self-citations that collapse the central claim are exhibited in the provided text. The chain is self-contained against the external benchmarks of the adopted coefficients and model.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The central claim depends on two adopted coefficient ranges and the domain assumption that MaMOS outgassing rates apply to white dwarf environments; no new entities are postulated.

free parameters (2)
  • SYORP coefficients = 10^{-5} to 10^{-3}
    Adopted range 10^{-5}–10^{-3} used to compute sublimative spin-up rate for the three materials.
  • YORP coefficients = 10^{-3} to 10^{-2}
    Adopted range 10^{-3}–10^{-2} for radiative spin-up comparison.
axioms (2)
  • domain assumption MaMOS model correctly quantifies outgassing properties of iron cores, forsterite mantles, and water-ice comets at white dwarf distances.
    Invoked to derive spin-up rates from sublimation.
  • domain assumption Planetesimals of radii 0.1, 1, and 10 km are either strengthless rubble piles or possess 1 kPa internal strength.
    Used to test sensitivity of fission timescales to internal strength.

pith-pipeline@v0.9.0 · 5898 in / 1604 out tokens · 61258 ms · 2026-05-21T03:11:59.982976+00:00 · methodology

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Works this paper leans on

1 extracted references · 1 canonical work pages

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    arXiv:2502.05502 Blackman J

    Aungwerojwit A., et al., 2024, MNRAS, 530, 117 Bertinelli G., Zhou W.-H., Tanga P., 2026, A&A, 707, A135 Bhattacharjee S., et al., 2025, arXiv e-prints, p. arXiv:2502.05502 Blackman J. W., et al., 2021, Nature, 598, 272 Bonsor A., 2026, in Encyclopedia of Astrophysics. pp 564–572, doi:10.1016/B978-0-443-21439-4.00020-1 BottkeJr.W.F.,VokrouhlickýD.,Rubinca...

    work page doi:10.1016/b978-0-443-21439-4.00020-1 2024