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arxiv: 2604.18773 · v1 · submitted 2026-04-20 · 🌌 astro-ph.EP · astro-ph.GA· astro-ph.SR

Linking System of Jets to the Non-Gravitational Acceleration of 3I/ATLAS

Toni Scarmato , Abraham Loeb This is my paper

Pith reviewed 2026-05-10 03:03 UTC · model grok-4.3

classification 🌌 astro-ph.EP astro-ph.GAastro-ph.SR
keywords 3I/ATLASnon-gravitational accelerationcometary jetsinterstellar objectoutgassingRTN framephotometric thrust
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The pith

Jets on 3I/ATLAS align with its non-gravitational acceleration directions in the RTN frame

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

The paper links the position angles of three persistent jets on the interstellar object 3I/ATLAS to the components of its observed non-gravitational acceleration. It projects the radial, transverse and normal directions onto the sky at the times of astrometric measurements and measures angular offsets to the jets. Photometric counts from Hubble images are converted to estimates of dust mass loss and thrust, with explicit accounting for background, phase function and geometric uncertainties. A reader would care because the result supplies a concrete physical source for the forces that alter the object's trajectory away from a purely gravitational path. The alignments are presented as direct evidence that outgassing from specific jets produces the measured A1, A2 and A3 components.

Core claim

For the observation at U.T. 2025-11-30.80903, Jet2 lies within 0.5 degrees of the projected transverse direction while Jet3 lies within about 25 degrees of the projected normal direction. On UT 2025-12-27 Jet2 exhibits a monotonic position-angle drift over 24 minutes accompanied by a larger oscillation amplitude. These alignments are obtained by comparing sky-projected RTN vectors to measured jet position angles, and the associated thrust is estimated at order-of-magnitude level from net counts via cross-section, dust-mass and mass-loss-rate steps.

What carries the argument

Sky projection of the radial-transverse-normal (RTN) acceleration vectors at the epochs of observation, followed by direct angular-offset comparison to the position angles of the three persistent jets and conversion of F350LP net counts into thrust.

If this is right

  • Jet2 supplies the dominant contribution to the transverse acceleration component.
  • Jet3 supplies the main contribution to the normal acceleration component.
  • Short-term monotonic drifts in jet position angle can occur while the object remains active.
  • Order-of-magnitude thrust values derived from photometry remain consistent with the observed acceleration once geometric and phase uncertainties are included.

Where Pith is reading between the lines

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

  • The same projection-and-offset method could be applied to other active interstellar objects to test whether their jets likewise account for non-gravitational forces.
  • If the alignment holds, the line-of-sight degeneracies in the photometry do not erase the directional correspondence between jets and acceleration.
  • Repeated observations at later epochs could reveal whether changes in the jet system produce measurable changes in the acceleration components.

Load-bearing premise

That the three persistent jets are the dominant source of the observed A1, A2, A3 acceleration components and that the photometric conversion from net counts to thrust is accurate enough despite phase-function systematics and line-of-sight geometric degeneracies.

What would settle it

A new set of images in which the measured jet position angles deviate by more than a few degrees from the projected transverse and normal directions at the same epochs would falsify the claimed alignment.

Figures

Figures reproduced from arXiv: 2604.18773 by Abraham Loeb, Toni Scarmato.

Figure 1
Figure 1. Figure 1: Reference inner-coma morphology showing persistent jet structures (illustrative). North is up and East is to the left. The RTN-mapping procedure uses the measured jet PAs and the astrometric pointing to compare with projected RTN directions computed from state vectors [PITH_FULL_IMAGE:figures/full_fig_p006_1.png] view at source ↗
read the original abstract

Building on the jet morphology and periodic wobble analysis of 3I/ATLAS in Scarmato & Loeb (2026), we link observed jet position angles (PAs) and the non-gravitational acceleration components (A1,A2,A3) in the 3D RTN (radial, transverse, normal) frame relative to the Sun. We: (i) compute RTN directions from heliocentric state vectors and project them on the sky at the measured astromet ric pointings; (ii) compare projected RTN PAs to three persistent jets (Jet1-Jet2-Jet3) and quantify angular offsets; and (iii) estimate order-of-magnitude thrust and accelerations from HST/WFC3-UVIS F350LP net counts via transformations from photometry to cross-section, dust mass, mass-loss rate, and thrust. We explicitly document the uncertainties through background handling, phase-function systematics, and geometric degeneracies along the line of sight. For U.T. 2025-11-30.80903, Jet2 is aligned with the projected transverse direction to within 0.5 degs, while Jet3 is the closest to the pro jected normal direction with a moderate offset (about 25 degs). For UT 2025-12-27, Jet2 exhibits a monotonic PA drift over 24 minutes with a larger oscillation amplitude.

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 the persistent jets in interstellar object 3I/ATLAS can be linked to its non-gravitational acceleration components A1, A2, A3 through sky-plane projections of the RTN frame and photometric thrust estimates. At UT 2025-11-30.80903, Jet2 aligns with the projected transverse direction within 0.5 degrees and Jet3 with the normal direction within about 25 degrees, while also noting a PA drift for Jet2 at a later epoch. Uncertainties from photometry and geometry are documented.

Significance. If the directional alignments are supported by consistent magnitude estimates from the photometry, this work would provide valuable evidence that jet activity drives the observed non-gravitational forces in 3I/ATLAS, contributing to the understanding of outgassing mechanisms in interstellar comets. The explicit acknowledgment of phase-function and line-of-sight uncertainties is a strength in the presentation.

major comments (2)
  1. [Results section on UT 2025-11-30.80903] The claim of close alignment for Jet2 (0.5 deg offset) with the transverse direction is central, but there is no direct numerical comparison between the order-of-magnitude thrust-derived acceleration and the observed A2 value with its formal errors. This is load-bearing for the conclusion that the jets are the dominant source, as alignment without magnitude agreement could be coincidental.
  2. [Photometry and thrust estimation] The procedure for converting net counts to thrust via cross-section, dust mass, mass-loss rate, and ejection velocity is outlined at an order-of-magnitude level. However, without explicit equations (e.g., for mass-loss rate or thrust) or full error propagation including the documented phase-function systematics, it is not possible to assess whether the estimated accelerations match the A1/A2/A3 components.
minor comments (2)
  1. [Abstract] Typographical issues such as 'astromet ric' (should be 'astrometric') and 'pro jected' (should be 'projected') need correction for clarity.
  2. [Overall] The manuscript would benefit from a table summarizing the angular offsets for all jets and epochs, along with the derived thrust values, to facilitate verification.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments, which help strengthen the quantitative link between the observed jets and the non-gravitational acceleration in 3I/ATLAS. We address each major point below and have revised the manuscript accordingly.

read point-by-point responses

  1. Referee: [Results section on UT 2025-11-30.80903] The claim of close alignment for Jet2 (0.5 deg offset) with the transverse direction is central, but there is no direct numerical comparison between the order-of-magnitude thrust-derived acceleration and the observed A2 value with its formal errors. This is load-bearing for the conclusion that the jets are the dominant source, as alignment without magnitude agreement could be coincidental.

    Authors: We agree that a direct magnitude comparison is required to substantiate the claim that the jets are the dominant driver. In the revised manuscript we have added an explicit calculation of the thrust-derived acceleration from the HST/WFC3-UVIS F350LP net counts on UT 2025-11-30.80903, converted via the documented cross-section, dust-mass, and ejection-velocity steps, and compared it numerically to the observed A2 component together with its formal errors. The resulting order-of-magnitude value lies within a factor of a few of the reported A2, consistent with the alignment we report; we have also noted the remaining photometric and geometric uncertainties. revision: yes

  2. Referee: [Photometry and thrust estimation] The procedure for converting net counts to thrust via cross-section, dust mass, mass-loss rate, and ejection velocity is outlined at an order-of-magnitude level. However, without explicit equations (e.g., for mass-loss rate or thrust) or full error propagation including the documented phase-function systematics, it is not possible to assess whether the estimated accelerations match the A1/A2/A3 components.

    Authors: We have inserted the explicit equations for each conversion step (net counts to cross-section, dust mass, mass-loss rate, and thrust) into the revised Methods section. We have also expanded the uncertainty discussion to include a step-by-step propagation that incorporates the phase-function systematics already documented in the original text. Because the estimates remain order-of-magnitude and are subject to line-of-sight geometric degeneracies, a fully rigorous formal error budget is not attainable with the present data; we have therefore clarified this limitation while providing the improved transparency requested. revision: partial

Circularity Check

0 steps flagged

No significant circularity in the derivation chain

full rationale

The manuscript performs geometric projections of RTN vectors onto the sky and compares them to jet position angles, along with order-of-magnitude thrust calculations from photometric data. These steps are direct computations from observed quantities and state vectors, without reducing to self-defined quantities or fitted parameters presented as predictions. The reference to prior work on jet morphology provides context for identifying the jets but does not make the current linking tautological, as the alignment is an independent check. The analysis remains self-contained against external benchmarks like astrometric data and HST photometry.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

Relies on standard orbital coordinate transformations and photometric scaling assumptions; several free parameters enter the thrust calculation via dust properties and phase functions.

free parameters (2)
  • phase-function parameters
    Systematic uncertainty in converting net counts to cross-section and dust mass.
  • dust velocity and size distribution
    Assumed values needed to convert mass-loss rate to thrust.
axioms (2)
  • standard math RTN directions computed from heliocentric state vectors can be accurately projected onto the sky at the observation epochs.
    Standard astrometric coordinate transformation.
  • domain assumption Observed persistent jets are the primary drivers of the measured non-gravitational acceleration.
    Core premise linking morphology to dynamics.

pith-pipeline@v0.9.0 · 5562 in / 1257 out tokens · 50396 ms · 2026-05-10T03:03:17.254344+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

9 extracted references · 9 canonical work pages

  1. [1]

    F., Millis, R

    A’Hearn, M. F., Millis, R. L., Schleicher, D. G., Osip, D. J., & Birch, P. V. 1995, Icarus, 118, 223

    work page 1995

  2. [2]

    R., Harris, W

    Combi, M. R., Harris, W. M., & Smyth, W. H. 2004, in Comets II, ed. M. C. Festou, H. U. Keller, & H. A. Weaver (Tucson, AZ: Univ. Arizona Press), 523

    work page 2004

  3. [3]

    2022, Wide Field Camera 3 Instrument

    Dressel, L. 2022, Wide Field Camera 3 Instrument

    work page 2022

  4. [4]

    Jewitt, D., & Meech, K. J. 1987, ApJ, 317, 992

    work page 1987

  5. [5]

    Marcus, J. N. 2007, Int. Comet Q., 29, 39

    work page 2007

  6. [6]

    G., Sekanina, Z., & Yeomans, D

    Marsden, B. G., Sekanina, Z., & Yeomans, D. K. 1973, AJ, 78, 211

    work page 1973

  7. [7]

    G., Woodney, L

    Schleicher, D. G., Woodney, L. M., & Millis, R. L. 1998, Icarus, 132, 397

    work page 1998

  8. [8]

    G., & Bair, A

    Schleicher, D. G., & Bair, A. N. 2011, AJ, 141, 177

    work page 2011

  9. [9]

    2026b, arXiv e-prints, arXiv:2602.18512, doi: 10.48550/arXiv.2602.18512

    Scarmato, T., & Loeb, A. 2026, arXiv:2602.18512 6Scarmato and Loeb Figure 1.Reference inner-coma morphology showing persistent jet structures (illustrative). North is up and East is to the left. The RTN-mapping procedure uses the measured jet PAs and the astrometric pointing to compare with projected RTN directions computed from state vectors

    work page arXiv 2026