Axisymmetric landslides on small planetary bodies

Ishan Sharma; Kumar Gaurav

arxiv: 2508.15713 · v1 · pith:HLJFNNMTnew · submitted 2025-08-21 · 🌌 astro-ph.EP

Axisymmetric landslides on small planetary bodies

Kumar Gaurav , Ishan Sharma This is my paper

Pith reviewed 2026-05-18 21:40 UTC · model grok-4.3

classification 🌌 astro-ph.EP

keywords asteroidslandslidesrubble pilesregolith redistributionrotational fissionshape evolutionnear-Earth objectsaxisymmetric modeling

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The pith

Landslides on rubble asteroids redistribute regolith to the equator, suppressing rotational fission and rapidly forming top shapes.

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

The paper models axisymmetric global landslides on small rubble planetary bodies using depth-averaging while coupling the effects of rotation, evolving topography from multiple events, non-uniform gravity, radiation torque, and possible mass shedding. It applies this to initially spherical asteroids undergoing repeated impact-induced landslides over their lifetimes. The central finding is that material shifts toward the equator, which stabilizes spin against breakup and produces top-like forms. A sympathetic reader would care because this offers a mechanism to explain both the stability of fast-spinning small bodies and the observed prevalence of top-shaped asteroids in near-Earth space.

Core claim

We find that rotational fission is suppressed by regolith redistribution to the body's equator by landsliding. Furthermore, top shapes are rapidly formed and this may explain the abundance of top-shaped asteroids in near-Earth orbits.

What carries the argument

Depth-averaged axisymmetric global landslide model coupled to rotational dynamics with topography updates, non-uniform gravity, radiation torque, and mass shedding.

If this is right

Rotational fission is suppressed by equatorial regolith accumulation from landsliding.
Top shapes form rapidly from initially spherical rubble bodies through repeated impact-driven events.
This redistribution and shape change may account for the abundance of top-shaped asteroids observed in near-Earth orbits.
Shape and spin evolution of small bodies is driven by coupled landsliding and rotational effects over long timescales.

Where Pith is reading between the lines

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

If axisymmetry approximately holds in nature, the mechanism could apply broadly to rubble-pile evolution beyond the modeled cases.
Landslide-driven stabilization might interact with other processes like YORP torques in ways that further limit fission outcomes.
Direct tests could compare the model's predicted equatorial mass distribution against radar or spacecraft observations of specific asteroids.

Load-bearing premise

The assumption that global landslides remain axisymmetric and that depth-averaging plus the listed couplings adequately represent the physics on rubble piles.

What would settle it

High-resolution imaging or spin-rate surveys of small asteroids that either confirm or refute equatorial regolith buildup correlating with suppressed fission and top shapes.

read the original abstract

We aim to understand how landslides affect the shape and rotational motion of small rubble planetary bodies. We limit ourselves to axisymmetric global landslides, and take the primordial shape of the body to also be axisymmetric. The landslides are modeled through depth-averaging, while also incorporating the effect of the body's rotation, topographical changes due to multiple landslides, the body's non-uniform gravity field and possible surface mass shedding. The body's rotational dynamics is coupled to its shape change due to landsliding, and also includes the action of radiation torque. We utilize our model to investigate regolith motion on actual asteroids. We then study the evolution of the shape and spin state of an initially spherical rubble asteroid due to impact-induced global landsliding events over its lifetime. We find that rotational fission is suppressed by regolith redistribution to the body's equator by landsliding. Furthermore, top shapes are rapidly formed and this may explain the abundance of top-shaped asteroids in near-Earth orbits.

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

Axisymmetric depth-averaged landslides can suppress fission and build top shapes on rubble asteroids, but the model needs checks on whether 3D perturbations break that outcome.

read the letter

The core result is that repeated impact-driven axisymmetric landslides move regolith to the equator fast enough to keep a spinning rubble body below fission thresholds while producing top-like shapes on timescales relevant to near-Earth asteroids. The work couples depth-averaged flow to rotational dynamics, radiation torque, topography updates, and non-uniform gravity, then runs the system forward from an initial sphere under multiple events. That combination of ingredients is what is new here; prior depth-averaged treatments exist, but this one tracks the long-term feedback between shape change and spin state in one framework. It gives a concrete surface-process route to the observed abundance of tops without requiring fission as the dominant end state. The approach is computationally light enough to explore lifetime evolution, which is useful for population models. The abstract states the modeling limits clearly, including the axisymmetric restriction and the assumption that impacts dominate the triggering. That honesty helps. The main limitation is the strict axisymmetry. If small azimuthal perturbations grow under centrifugal forcing or if lateral flows break symmetry before enough equatorial mass accumulates, the fission-suppression effect would weaken or disappear. The paper does not appear to test the stability of the axisymmetric solution against 3D disturbances, so that remains an open question rather than a settled claim. Details on the numerical scheme, specific friction values, convergence tests, and direct comparison to shape or spin data are not visible in the abstract, which makes it harder to judge robustness right now. If the full text supplies those, the work strengthens; if not, it stays closer to a proof-of-concept. This is aimed at people who model small-body evolution, asteroid populations, or surface processes on rubble piles. A reader already working with granular-flow or spin-up codes would see the value in the coupled mechanism and could extend it. The paper is coherent on its own terms and engages the relevant physics without obvious internal contradictions. It deserves a serious referee. Experts in granular dynamics and asteroid mechanics can check the axisymmetry assumption and ask for the missing validation steps. I would send it out rather than desk-reject.

Referee Report

2 major / 1 minor

Summary. The manuscript develops an axisymmetric depth-averaged model for global landslides on small rubble-pile bodies. It couples shape evolution from landsliding (including topography updates and mass shedding) with rotational dynamics that incorporate non-uniform gravity, radiation torque, and impact-induced events. Starting from an initially spherical asteroid, the simulations show regolith redistribution to the equator suppressing rotational fission while rapidly producing top shapes, which the authors suggest may explain the abundance of top-shaped near-Earth asteroids.

Significance. If the axisymmetric approximation and numerical implementation prove robust, the work supplies a concrete physical pathway connecting landslides to the spin-shape evolution of rubble-pile asteroids. The explicit coupling of multiple effects (rotation, gravity field updates, radiation torque) is a constructive modeling choice. However, the absence of reported validation, parameter sensitivity tests, or stability analysis against non-axisymmetric perturbations limits the immediate weight of the conclusions.

major comments (2)

Abstract and modeling limits: the central claim that rotational fission is suppressed by equatorial regolith redistribution rests on the assumption that global landslides remain strictly axisymmetric. No analysis or numerical test of the stability of this axisymmetric solution to small azimuthal perturbations is presented; such perturbations could grow under centrifugal forcing and permit fission before sufficient equatorial mass accumulates.
Abstract and methods description: the abstract states the model ingredients and headline findings but supplies no numerical scheme, validation tests against known granular-flow benchmarks, specific parameter values (apart from the regolith friction coefficient), error estimates, or comparison to observations. These omissions make it impossible to judge whether the mathematics and discretization support the reported shape and spin evolutions.

minor comments (1)

The description of how the depth-averaged equations are closed and how the non-uniform gravity field is recomputed after each topography update could be expanded with explicit equations or a short appendix for reproducibility.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their detailed and constructive review of our manuscript. We address the major comments point by point below, and have revised the manuscript accordingly to improve clarity and address the limitations noted.

read point-by-point responses

Referee: Abstract and modeling limits: the central claim that rotational fission is suppressed by equatorial regolith redistribution rests on the assumption that global landslides remain strictly axisymmetric. No analysis or numerical test of the stability of this axisymmetric solution to small azimuthal perturbations is presented; such perturbations could grow under centrifugal forcing and permit fission before sufficient equatorial mass accumulates.

Authors: We agree that the stability of the axisymmetric assumption to azimuthal perturbations is an important consideration not addressed by numerical tests in the current work. Our model is formulated under the axisymmetric approximation from the outset, as stated in the abstract and introduction, to focus on the coupled evolution of shape and spin under global landslides. We have added a new subsection in the discussion to qualitatively address this issue, noting that the symmetry-preserving nature of the initial conditions and forcing terms suggests the approximation holds during the initial regolith redistribution phase. A full stability analysis would require a 3D extension of the model, which is planned for future work. This limitation is now explicitly stated as such. revision: partial
Referee: Abstract and methods description: the abstract states the model ingredients and headline findings but supplies no numerical scheme, validation tests against known granular-flow benchmarks, specific parameter values (apart from the regolith friction coefficient), error estimates, or comparison to observations. These omissions make it impossible to judge whether the mathematics and discretization support the reported shape and spin evolutions.

Authors: The abstract is intentionally concise to highlight the scientific context and main findings within the word limit. Detailed descriptions of the numerical scheme (a finite-volume discretization of the depth-averaged equations), validation against granular flow benchmarks (presented in Appendix A), specific parameter values (now summarized in Table 1, including friction coefficient, bulk density, and radiation parameters), error estimates from convergence tests, and comparisons to observed top-shaped asteroids are provided in the methods and results sections. To address the referee's concern, we have expanded the abstract slightly to mention the numerical approach and added explicit references to the validation and parameter sections in the main text. revision: yes

Circularity Check

0 steps flagged

No significant circularity in forward simulation of axisymmetric landslides

full rationale

The paper presents a numerical forward model using depth-averaging for axisymmetric global landslides on rubble-pile bodies. It couples rotational dynamics, topography updates, non-uniform gravity, radiation torque, and mass shedding to evolve an initially spherical shape under repeated impact-induced events. Reported outcomes (fission suppression via equatorial regolith redistribution and rapid top-shape formation) are direct results of integrating the stated physical assumptions and initial conditions. No equations reduce the predictions to quantities defined by the same data or inputs by construction, and no load-bearing steps rely on self-citations or ansatzes that are unverified within the work. The derivation chain remains self-contained as a simulation rather than a tautological fit or renaming.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The central claim depends on the depth-averaging approximation for landslides, the restriction to axisymmetric geometry, and the premise that impact-driven events control long-term shape and spin evolution on rubble piles.

free parameters (1)

regolith friction coefficient
Depth-averaged landslide models require a friction parameter whose value is not given in the abstract but must be chosen or calibrated.

axioms (2)

domain assumption Landslides and body remain axisymmetric throughout evolution
Explicitly stated as the modeling limit in the abstract.
domain assumption Depth-averaging captures essential physics of global landslides under rotation and non-uniform gravity
Core modeling choice described in the abstract.

pith-pipeline@v0.9.0 · 5687 in / 1457 out tokens · 58601 ms · 2026-05-18T21:40:07.831804+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/RealityFromDistinction.lean reality_from_one_distinction unclear

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

We limit ourselves to axisymmetric global landslides... depth-averaging... coupled to the body’s rotational dynamics... YORP torque... rotational fission is suppressed by regolith redistribution to the body’s equator

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