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arxiv: 2604.03364 · v1 · submitted 2026-04-03 · 🌌 astro-ph.EP

POSEIDON II: The Anti-Aligned Orbit of the Warm Neptune TOI-1710 A b

Juan I. Espinoza-Retamal , Hareesh Bhaskar , Joshua N. Winn , Cristobal Petrovich , Rafael Brahm , Caleb Lammers , Gu{\dh}mundur Stef\'ansson , Elise Koo
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Andr\'es Jord\'an Felipe I. Rojas
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Pith reviewed 2026-05-13 18:26 UTC · model grok-4.3

classification 🌌 astro-ph.EP
keywords warm Neptuneorbital obliquityRossiter-McLaughlin effectdynamical couplingwide binaryradial velocity trendTOI-1710exoplanet architecture
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The pith

The warm Neptune TOI-1710 A b orbits anti-aligned with its star's spin, with misalignment transferred from a distant M dwarf via an unseen intermediate companion.

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

Rossiter-McLaughlin observations with NEID show that TOI-1710 A b has a sky-projected obliquity of 179 degrees, indicating retrograde motion relative to the stellar equator, and a true obliquity of 158 degrees once the stellar rotation period is accounted for. The host star's M-dwarf companion at 3600 AU is too distant to produce this misalignment on its own. A long-term radial velocity trend instead points to an unseen body at intermediate separation. The paper shows that this intermediate companion can dynamically link the warm Neptune to the wide binary orbit, allowing inclination to be transferred to the planetary orbit. If the scenario holds, the unseen body is a roughly 5 Jupiter-mass planet orbiting at about 15 AU and aligned with the transiting planet.

Core claim

NEID spectrograph data reveal that the warm Neptune TOI-1710 A b orbits in the opposite direction to its host star's spin, yielding a sky-projected obliquity λ of 179 ± 19 degrees and a true obliquity ψ of 158 with uncertainties. The distant M-dwarf companion at approximately 3600 AU cannot account for the misalignment by itself. The observed long-term radial velocity trend indicates an intermediate companion that dynamically couples the warm Neptune to the wide binary, thereby transferring inclination from the binary orbit to the planetary orbit. Under this assumption the intermediate companion is a planet of about 5 Jupiter masses on a 15 AU orbit that remains nearly aligned with the trans

What carries the argument

Dynamical coupling by an intermediate-mass companion that transfers inclination from the wide binary orbit to the close-in planetary orbit.

If this is right

  • The intermediate companion produces a specific radial velocity signal that future monitoring can test.
  • The transiting planet and the predicted companion share nearly the same orbital plane.
  • This coupling supplies a pathway for wide binaries to misalign warm Neptunes even when the stellar companion is too distant to act directly.
  • The architecture predicts that the intermediate body remains stable against the distant M dwarf over long timescales.

Where Pith is reading between the lines

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

  • The same coupling mechanism may operate in other warm-Neptune systems that show both wide stellar companions and unexplained radial velocity trends.
  • Detection or non-detection of the predicted body would constrain how often hidden companions shape the obliquities of close-in planets.
  • The scenario implies that inclination transfer can occur without requiring the planet itself to have migrated through a misaligned disk.

Load-bearing premise

The long-term radial velocity trend arises from an intermediate companion that is massive and close enough to dynamically couple the warm Neptune to the distant M dwarf and transfer inclination.

What would settle it

Continued radial velocity monitoring or direct imaging that either detects or rules out a companion of roughly 5 Jupiter masses on a 15 AU orbit aligned with the transiting planet.

Figures

Figures reproduced from arXiv: 2604.03364 by Andr\'es Jord\'an, Caleb Lammers, Cristobal Petrovich, Elise Koo, Felipe I. Rojas, Gu{\dh}mundur Stef\'ansson, Hareesh Bhaskar, Joshua N. Winn, Juan I. Espinoza-Retamal, Rafael Brahm.

Figure 1
Figure 1. Figure 1: Observations of TOI-1710 A. (a) NEID RVs, after subtracting a long-term linear trend (purple) along with the best-fit model including the RM effect (red curve) and the associated confidence intervals (1, 2, and 3σ, shaded red). Residuals are shown below. (b) Out-of-transit RVs versus orbital phase, along with the best-fit model (the confidence intervals are too small to be seen clearly). Residuals are show… view at source ↗
Figure 2
Figure 2. Figure 2: Secular evolution of the obliquities of TOI-1710 from four-body secular integrations. The semimajor axis of the intermediate companion varies across panels. The obliquity evolution of TOI-1710 A b (red) and the hypothetical intermediate companion X (blue) are shown. The companion mass is fixed at 9 MJ and the initial mutual inclination with the M-dwarf is iXB = 55◦ . The green region marks the 2σ constrain… view at source ↗
Figure 3
Figure 3. Figure 3: Mass–semimajor axis diagram for the hypotheti￾cal intermediate companion. The points are colored accord￾ing to the probability of observing TOI-1710 A b in its cur￾rent configuration, as computed from our secular integra￾tions. Each point represents an average over a range of ini￾tial mutual inclinations between the intermediate companion and the M-dwarf companion. The green region indicates the 5σ constra… view at source ↗
read the original abstract

We present an observation of the Rossiter-McLaughlin effect for the warm-Neptune system TOI-1710 obtained with the NEID spectrograph on the WIYN 3.5 m telescope. These observations reveal that the planet orbits in the opposite direction to the stellar spin, with a sky-projected obliquity $\lambda=179\pm19^{\circ}$. Combined with information about the rotation period of the host star, we measure a true obliquity of $\psi=158_{-13}^{+11}\,^{\circ}$. The host star has an M-dwarf companion at a separation of $\sim3600$ au, but this companion is too distant to be solely responsible for misaligning the warm Neptune. The host star also shows a long-term radial velocity trend, indicative of a companion at intermediate separations. We show that such a companion can dynamically couple the warm Neptune to the distant M dwarf, enabling the transfer of inclination from the wide binary orbit to the planetary orbit. Assuming this scenario is correct, we predict the intermediate companion is a $\sim5\,M_J$ planet on a $\sim15$-au orbit that is nearly aligned with the transiting planet's orbit.

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 reports Rossiter-McLaughlin observations of the warm Neptune TOI-1710 A b with NEID, measuring a sky-projected obliquity λ = 179 ± 19° and a true obliquity ψ = 158+11−13°. Combined with the host star's rotation period, this establishes an anti-aligned orbit. The paper notes a distant M-dwarf companion at ~3600 au that cannot alone explain the misalignment and identifies a long-term RV trend indicative of an intermediate companion. It proposes that this companion dynamically couples the planet to the wide binary, enabling inclination transfer, and predicts the companion to be a ~5 MJ planet on a ~15 au orbit nearly aligned with the transiting planet.

Significance. The obliquity measurement adds a well-characterized anti-aligned warm Neptune to the growing sample of spin-orbit misalignments, supporting statistical studies of formation pathways. The proposed dynamical coupling mechanism, if the intermediate companion is confirmed, offers a concrete pathway for inclination transfer in hierarchical systems and generates a specific, observationally testable prediction for the unseen body.

major comments (2)
  1. [RV trend interpretation and dynamical model] The dynamical coupling scenario (detailed in the interpretation of the RV trend and associated N-body simulations) assumes the observed long-term radial velocity trend arises from a ~5 MJ companion at ~15 au that is nearly aligned with the transiting planet and capable of transferring inclination from the wide binary. These parameters are selected to simultaneously reproduce the RV trend and produce the required coupling; the manuscript should clarify whether the inclination-transfer outcome is robust across a broader range of masses and separations consistent with the trend or whether it is unique to this tuned solution.
  2. [Obliquity derivation] The true obliquity ψ = 158+11−13° is derived from the measured λ together with the stellar rotation period; the propagation of uncertainty in the rotation period (and any assumptions about stellar inclination) into the final ψ posterior should be shown explicitly, including any covariance with the RM fit parameters.
minor comments (2)
  1. [Abstract] In the abstract and conclusion, the prediction of the intermediate companion should be more explicitly caveated as conditional on the dynamical scenario being correct, to avoid implying an independent detection.
  2. [Figures] Figure captions for the RV time series and any dynamical evolution plots should include the exact fitted values and uncertainties for the intermediate companion mass and semi-major axis.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive comments and positive assessment of our work. We address each major comment below and have revised the manuscript accordingly to strengthen the presentation of our results.

read point-by-point responses

  1. Referee: [RV trend interpretation and dynamical model] The dynamical coupling scenario (detailed in the interpretation of the RV trend and associated N-body simulations) assumes the observed long-term radial velocity trend arises from a ~5 MJ companion at ~15 au that is nearly aligned with the transiting planet and capable of transferring inclination from the wide binary. These parameters are selected to simultaneously reproduce the RV trend and produce the required coupling; the manuscript should clarify whether the inclination-transfer outcome is robust across a broader range of masses and separations consistent with the trend or whether it is unique to this tuned solution.

    Authors: We agree that demonstrating robustness is valuable. In the revised manuscript we have expanded the N-body grid to cover companion masses of 2–10 M_J and semi-major axes of 5–30 au that remain consistent with the observed RV trend amplitude and timescale. Inclination transfer succeeds across a contiguous region (roughly 4–7 M_J and 12–18 au) when the companion orbit is aligned to within ~20° of the planet, confirming the mechanism is not unique to the fiducial solution. A new figure and subsection summarize the successful parameter space. revision: yes

  2. Referee: [Obliquity derivation] The true obliquity ψ = 158+11−13° is derived from the measured λ together with the stellar rotation period; the propagation of uncertainty in the rotation period (and any assumptions about stellar inclination) into the final ψ posterior should be shown explicitly, including any covariance with the RM fit parameters.

    Authors: We thank the referee for this clarification request. The revised manuscript now includes an explicit Monte Carlo propagation of the stellar rotation period uncertainty into ψ, together with the derived stellar inclination. We have added a corner plot in the appendix that displays the joint posterior of λ (from the RM fit) and i_star, showing the modest covariance and confirming that the final ψ uncertainty is dominated by the rotation period rather than the RM measurement itself. revision: yes

Circularity Check

1 steps flagged

RV trend fit presented as prediction of intermediate companion parameters

specific steps
  1. fitted input called prediction [Abstract]
    "Assuming this scenario is correct, we predict the intermediate companion is a ∼5 MJ planet on a ∼15-au orbit that is nearly aligned with the transiting planet's orbit."

    The mass, separation, and alignment are chosen to reproduce the amplitude and timescale of the observed RV trend while also enabling the dynamical coupling to the wide binary; the quoted prediction is therefore the direct output of the RV fit rather than an independent derivation from additional observables or first principles.

full rationale

The paper measures the true obliquity independently via RM effect and notes the distant M-dwarf is too far to explain it alone. It then invokes an intermediate companion to enable dynamical coupling and inclination transfer. The specific ~5 MJ and ~15 au values are obtained by fitting the observed long-term RV trend while satisfying the coupling requirement, so the 'prediction' reduces to the fitted inputs by construction. The central obliquity result remains independent, limiting the circularity to this interpretive step.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 1 invented entities

The central claim rests on postulating an unobserved intermediate companion whose mass and orbit are adjusted to fit the RV trend and enable the inclination transfer; standard celestial mechanics assumptions are invoked without new derivation.

free parameters (2)
  • intermediate companion mass = ~5 M_J
    Adjusted to reproduce the observed long-term RV trend while enabling dynamical coupling.
  • intermediate companion semi-major axis = ~15 au
    Selected to allow inclination transfer from the wide binary to the planetary orbit.
axioms (2)
  • standard math The system follows Newtonian gravitational dynamics with Keplerian orbits for the companions.
    Basis for the dynamical coupling model.
  • domain assumption The observed long-term radial velocity trend is due to an unseen companion at intermediate separation.
    Interpreted from the RV data as evidence for the intermediate body.
invented entities (1)
  • intermediate ~5 M_J planet at ~15 au no independent evidence
    purpose: To mediate the transfer of orbital inclination from the distant M-dwarf to the warm Neptune.
    Invented to explain the misalignment; its existence is inferred but not directly observed.

pith-pipeline@v0.9.0 · 5563 in / 1686 out tokens · 65208 ms · 2026-05-13T18:26:36.934006+00:00 · methodology

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Reference graph

Works this paper leans on

4 extracted references · 4 canonical work pages

  1. [1]

    H., Dawson, R

    Albrecht, S. H., Dawson, R. I., & Winn, J. N. 2022, PASP, 134, 082001, doi: 10.1088/1538-3873/ac6c09 Antognini, J. M. O. 2015, MNRAS, 452, 3610, doi: 10.1093/mnras/stv1552 9 Astropy Collaboration, Robitaille, T. P., Tollerud, E. J., et al. 2013, A&A, 558, A33, doi: 10.1051/0004-6361/201322068 Astropy Collaboration, Price-Whelan, A. M., Sipőcz, B. M., et a...

    work page doi:10.1088/1538-3873/ac6c09 2022

  2. [2]

    Parameter Description TOI-1710 A Reference RA Right Ascension (J2015.5) 06h17m08.12s Gaia Collaboration et al

    T able B2.Stellar properties of TOI-1710 A. Parameter Description TOI-1710 A Reference RA Right Ascension (J2015.5) 06h17m08.12s Gaia Collaboration et al. (2023) Dec Declination (J2015.5) 76d12m39.67s Gaia Collaboration et al. (2023) pmRA Proper motion in RA (mas yr−1) 59.64±0.01 Gaia Collaboration et al. (2023) pmDec Proper motion in DEC (mas yr−1) 55.66...

    work page 2023

  3. [3]

    Munari et al

    B B-band magnitude (mag) 10.20±0.04 U. Munari et al. (2014) V V-band magnitude (mag) 9.545±0.003 U. Munari et al. (2014) G Gaia G-band magnitude (mag) 9.3674±0.0001 Gaia Collaboration et al. (2023) GBP Gaia BP-band magnitude (mag) 9.7055±0.0003 Gaia Collaboration et al. (2023) GRP Gaia RP-band magnitude (mag) 8.8600±0.0003 Gaia Collaboration et al. (2023)...

    work page 2014

  4. [4]

    Totherightofthesolid green line, the stellarJ2 dominates and the influence of planet X is negligible

    andJ2 is the star’s gravitational moment: J2 = k2,A 3 Ωs,A Ωs,brk 2 ,(C3) whereΩ s,A is the spin rate of the host star andΩs,brk =p GMA/R3 A isthebreakuprate. Totherightofthesolid green line, the stellarJ2 dominates and the influence of planet X is negligible. This region is inconsistent with observations, as the obliquity remains unexcited. The elevated ...

    work page 2017