{"id":"f9f4d363-fad4-4786-abd5-b250e9f35fec","arxiv_id":"2507.11693","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Tidal disruption of a close-in giant planet can deliver H/He gas to an outer low-mass planet, forming a transient detectable atmosphere for up to 100 million years.","lead":"This paper proposes that when a close-in giant planet is torn apart by its star, the expelled hydrogen and helium can drift outward and be captured by a small outer planet. Those captured gases could form a temporary atmosphere, detectable in transit, and may explain some puffy, volatile-rich exoplanets like WASP-107b and TOI-421b.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The claimed VEP envelope masses are gas counts inside an unvalidated empirical capture radius (0.2 RH), with no demonstration that the gas is gravitationally bound; a retention test is needed before the quantitative claims hold.","rationale":"The paper proposes a physically plausible and novel pathway: gas released by the tidal disruption of a close-in giant planet can spread outward in a viscous disc and be gravitationally captured by an exterior low-mass planet, producing a transient, volatile-rich atmosphere. The 2D hydrodynamical simulations clearly demonstrate outward gas diffusion and local density enhancements near the planet, and the N-body stability analysis supports the assumed architecture. I agree with the reader that the qualitative mechanism is viable and that the paper should not be rejected outright. However, the quantitative claims, including the headline envelope masses up to 10^-6 Earth masses and the transit depths of tens to hundreds of ppm, depend critically on interpreting the gas column density inside Rcap = 0.2 RH as an actual bound atmosphere. The paper does not check whether this gas is bound in the Hill-sphere sense, and the empirical calibration of Rcap comes from a co-authored paper without a sensitivity study. The internal Hill-radius arithmetic error in Table A.2 for the 10 Earth-mass cases further weakens confidence in the reported numbers. These issues are addressable with additional post-processing or targeted simulations, so a conditional acceptance is appropriate. The proposed Jacobi-constant test provides a direct, computationally feasible check that would settle whether the counted gas is genuinely retained as an envelope.","tokens_in":10036,"tokens_out":23293,"duration_ms":270540,"concrete_test":"Using the saved FARGO3D snapshots for the closest configuration (10 Earth masses, a = 0.04 au, reported captured mass 4.58e-6 Earth masses), compute the Jacobi constant C for every cell within Rcap in the planet's rotating frame. Integrate the mass with C below the critical value defining the Roche lobe, giving the gravitationally bound mass, and compare it with the total gas mass inside Rcap used in Table 1. If the bound fraction is less than 50%, then Eq. (1) overestimates the retained atmosphere, and the transit depth and persistence claims are unsupported; if the bound fraction is near unity, the VEP envelope masses are credible.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central quantitative claim, captured envelopes of up to 10^-6 Earth masses and transit depths of tens to hundreds of ppm, rests on Eq. (1), which defines the envelope mass as all gas inside Rcap = 0.2 RH in the 2D FARGO3D surface density field. The paper does not demonstrate that this gas is gravitationally bound to the planet and would remain if the circumstellar disc dispersed. In an isothermal, non-accreting hydrodynamical run, gas within the Hill sphere includes unbound horseshoe and shear-flow material; the instantaneous column density inside a fixed radius is not an atmospheric mass. The empirical Rcap is taken from a co-authored calibration (Montesinos et al. 2025) without independent validation or a sensitivity study. Table A.2 also contains a Hill-radius arithmetic error for the 10 Earth-mass cases (1.5e-4 au versus the correct 8.6e-4 au at 0.04 au). The transit depth estimate in Appendix C assumes a spherical, hydrostatic, isothermal atmosphere, whereas the simulated gas distribution is a 2D disc-like flow; the relationship between the counted mass and the effective scale height is unverified. If the bound fraction is significantly below unity, the quoted masses, transit depths, and persistence timescales, which all use these masses as atmospheric masses, shrink correspondingly.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This Letter proposes that the tidal disruption of a close-in giant planet produces a volatile-rich gas ring that spreads outward and can be gravitationally captured by a low-mass outer planet, forming a transient H/He-rich envelope: a 'volatile-enriched planet' (VEP). The authors use 2D FARGO3D hydrodynamical simulations of the gas ring, N-body simulations with REBOUND to assess orbital stability, and analytical models for envelope contraction, XUV-driven escape, and transit spectroscopy. They report captured envelope masses of 10^-10 to 10^-6 Earth masses, transit depths of tens to hundreds of parts per million, and persistence timescales of 10^6 to 10^8 years, and they suggest that systems such as TOI-421b and WASP-107b may be explained by this mechanism. The central quantitative claims, however, rest on an empirical capture radius, a 2D-to-3D extrapolation, and a Hill-radius arithmetic error that materially affects the 10 Earth-mass cases.","tokens_in":10363,"tokens_out":5578,"duration_ms":65266,"significance":"If the proposed mechanism is physically correct, it offers a novel and falsifiable pathway for the formation of H/He-rich secondary atmospheres on low-mass planets, with clear observational predictions (transit depth, He I 10830 Angstrom absorption, and eccentric orbits) that connect tidal disruption events to the population of inflated sub-Neptunes. The hydrodynamic demonstration that disrupted gas spreads outward on a short timescale is a genuine strength, and the paper is clearly written with a well-defined question. However, the quantitative envelope masses and transit depths are not yet supported: they depend on an empirically calibrated capture radius, on counting all gas inside that radius without demonstrating gravitational binding, and on a spherical-atmosphere model applied to a 2D surface-density flow. These issues are load-bearing for the paper's central claim, so the result is plausible but not yet established.","major_comments":[{"comment":"The envelope mass is defined as the total gas mass inside Rcap = 0.2 RH, where the factor 0.2 is an empirical scale taken from Montesinos et al. (2025) without derivation or sensitivity analysis. Because all quantitative results in Table 1 and Section 3 scale with this radius, the paper needs either an independent physical justification for Rcap/RH or a sensitivity study (e.g., varying Rcap from 0.05 to 0.5 RH). More importantly, the manuscript does not demonstrate that the gas counted inside Rcap is gravitationally bound to the planet rather than transient shear flow or horseshoe material; a bound-mass criterion (e.g., bound-energy or particle-trajectory analysis) should be applied to the simulation output before the quoted masses can be interpreted as atmospheric masses.","section":"Section 2, Eq. (1)"},{"comment":"The Hill radius quoted for the 10 Earth-mass planet at a = 0.04 au is 1.5e-4 au, but the stated formula RH = a(Mp/3Mstar)^(1/3) gives approximately 8.6e-4 au; the tabulated value is too small by a factor of about 5.7. This error propagates directly into Rcap = 0.2 RH and hence into the 10 Earth-mass captured masses and transit depths in Table 1. The 10 Earth-mass calculations must be redone with the correct Hill radius, and the revised numbers should be reported.","section":"Table A.2"},{"comment":"The transit-depth estimate uses a spherical, hydrostatic, isothermal atmosphere with a base density rho0 and atmospheric mass Matm (Eqs. C.1-C.5). The simulation, however, provides a 2D surface-density distribution in a disc-like flow with no vertical structure, and Eq. (1) counts surface density inside Rcap. No mapping is given from the simulated 2D mass to the spherical atmospheric mass used in Eq. (C.3), so the effective height AH and transit depth DeltaF are not derivable from the simulation as presented. The authors should either perform a 3D model or provide an explicit, justified conversion that accounts for the vertical structure, temperature, and opacity.","section":"Section 3.2 and Appendix C"},{"comment":"The persistence timescales of 10^6 to 10^8 years are obtained from mass-loss rates taken from Eq. (12) of Alvarado-Montes et al. (2025), a companion paper. The applicability of that formalism to the specific parameter space considered here (1-10 Earth-mass planets at 0.04-0.07 au around a solar-type star) is not demonstrated in this manuscript. Since the observability claim depends on these long persistence timescales, the essential mass-loss equations and the adopted input values should be reproduced in an appendix, or a clear validity argument for this parameter range should be provided.","section":"Section 3.3"},{"comment":"The accretion prescription Mdot = Menv(t)/tKH is used with tKH ~ 10^8 yr for a 1 Earth-mass core, while the gas disc disperses on t_nu ~ 163 yr (Section 3.4). Integrating Mdot over the disc lifetime gives an accreted mass of order Menv * 163/10^8, which is negligible compared with the instantaneous Menv values quoted in Table 1. The paper does not specify at which time the 'captured mass' in Table 1 is evaluated, nor how the instantaneous count of gas inside Rcap becomes the final, persistently bound envelope mass. This logical gap should be addressed, either by revising the accretion model or by clarifying that the quoted masses are instantaneous hydrodynamical gas counts, not necessarily retained atmospheres.","section":"Section 2, Eqs. (2)-(3)"}],"minor_comments":[{"comment":"The text says 'the accretion rate peak of Fig. 2.b', but Fig. 2.b is the density evolution panel; the accretion rate and envelope mass are shown in Fig. 2.c. The cross-reference should be corrected.","section":"Section 3.1"},{"comment":"The text refers to 'Fig. B' for eccentricity excitation; the relevant figure is Fig. B.2 (and the MEGNO maps are Fig. B.1). The cross-references should be made precise.","section":"Section 3.5"},{"comment":"In Eq. (C.2), the term 'p2πRpH' is a typographical rendering of sqrt(2π R_p H); the typeset version should use a proper square-root symbol to avoid confusion.","section":"Appendix C"},{"comment":"Several superscripts are lost in the text version (e.g., '10−10–10−6, M⊕' and '106–108 years'); the published version must format these as 10^-10-10^-6 and 10^6-10^8 years.","section":"Throughout"},{"comment":"Minor typographical issues: 'W ASP-107b' should read 'WASP-107b', and 'HAT-P-11b' has an extra space in the Introduction. These should be corrected during production.","section":"Throughout"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a Letter that draws two key quantitative inputs (Rcap and mass-loss rates) from companion papers by the same group, and one of its own table entries (Hill radius for 10 M_Earth) contains a factor-of-5.7 arithmetic error. These issues, together with the absence of a gravitational-binding test for the counted gas, make the headline numbers (10^-6 M_Earth envelopes, hundreds of ppm transit depths, 10^8 yr persistence) not yet supported. I believe the errors are fixable within the scope of a revision, but the authors should be asked to provide a sensitivity analysis for Rcap, a bound-mass demonstration, corrected Hill radii, and a clearer connection between the 2D simulation masses and the spherical-atmosphere transit model. This is a case where the qualitative idea is appealing but the quantitative claims need substantial additional support before acceptance."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nYou should know two things about this paper: the idea is genuinely novel, and the numbers should not be trusted yet.\n\nWhat's new: they propose that when a close-in giant planet is tidally disrupted, the H/He gas released can migrate outward and be captured by a low-mass planet, creating a transient 'volatile-enriched planet' (VEP). They back this with 2D FARGO3D simulations showing the gas spreading out and entering the Hill region of a 1–10 M_Earth planet, plus N-body stability maps and rough transit-depth and mass-loss estimates. The scenario is not in the cited literature, which focuses on stellar pollution and debris disks. The physics ingredients are standard, so this is a solid new application rather than a revolution. The paper is clearly written and the figures help.\n\nThe soft spots are mainly quantitative. The key number, the envelope mass, comes from Eq. (1): everything inside Rcap = 0.2 R_H is counted as accreted. That capture radius is taken from a coauthored calibration (Montesinos et al. 2025) and there is no sensitivity study around it. More importantly, there is no demonstration that the gas inside Rcap is actually gravitationally bound to the planet. In an isothermal, non-accreting hydro run, the Hill sphere contains unbound shear-flow and horseshoe material. Counting column density inside a fixed radius is not the same as an atmospheric mass. If the bound fraction is significantly below unity, the quoted masses, transit depths, and persistence times all shrink. This is the load-bearing issue.\n\nThere are also smaller problems. Table A.2 gives the Hill radius for a 10 M_Earth planet at 0.04 au as 1.5e-4 au; the correct value is about 8.6e-4 au, a factor of 5.7. The transit depth estimate assumes a spherical, hydrostatic, isothermal atmosphere, but the simulated gas is a 2D disc-like flow; the mapping between counted mass and scale height is unverified. And the viscous timescale argument (t_nu ~ 163 yr) seems at odds with the statement that gas reaches the outer planet within ~3 years, though that may just be a fast initial spreading.\n\nNone of this kills the qualitative mechanism. It is a plausible pathway, and the paper is honest about being a Letter-scale exploration. But the quantitative claims need to be verified with a proper retention check (e.g., 3D simulations or an energy criterion) and sensitivity tests on Rcap and viscosity.\n\nWho should read this? Anyone working on inflated sub-Neptunes, atmospheric escape, or late-stage planetary system evolution. It gives a fresh interpretation for systems like WASP-107b and TOI-421b, even if the match is speculative.\n\nMy recommendation: accept it for peer review. The idea deserves referee time. But expect major revisions. The authors need to either justify Rcap physically, run a bound-fraction test, or substantially soften the quantitative claims.","headline":"A genuinely new capture mechanism with numbers that need a binding-check before you quote them.","tokens_in":10867,"tokens_out":3493,"would_cite":false,"duration_ms":37359,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Tidal disruption of a close-in giant planet can deliver enough hydrogen and helium to a surviving low-mass planet to form a detectable secondary atmosphere lasting up to 100 million years.","keywords":["tidal disruption","volatile-enriched planets","secondary atmospheres","hydrogen-helium envelopes","transit spectroscopy","planet-star interactions","planetary engulfment","warm sub-Neptunes"],"falsifier":"Run a 3D hydrodynamical simulation that tracks whether gas entering the 0.2-Hill-radius zone remains gravitationally bound to the planet after the viscous disk disperses, or take a high-sensitivity transmission spectrum of a 1 to 10 Earth-mass planet at 0.04 to 0.07 au in a system with a recent giant disruption and check whether the predicted tens-to-hundreds of parts per million H/He signal is present.","tokens_in":1812,"feed_emoji":"🪐","tokens_out":2039,"duration_ms":92072,"temperature":0.7,"pith_summary":"The paper asks what happens to the gas of a giant planet that is tidally destroyed by its star. It argues that this hydrogen- and helium-rich gas spreads outward through the disk and can be captured by a low-mass planet on a wider orbit. The captured gas forms a thin secondary atmosphere, up to about a millionth of an Earth mass, which could be seen in transit as a signal of tens to hundreds of parts per million. Because such atmospheres can survive for one to one hundred million years, they remain observable long after the disruption event itself has faded. If true, this gives a new way to explain warm, low-density exoplanets with hydrogen-rich atmospheres and moderate eccentricities, such as TOI-421b and WASP-107b.","feed_headline":"Tidal death of a gas giant can gift a new atmosphere","feed_subtitle":"Transit signals of tens to hundreds of parts per million could reveal atmospheres from past planetary disruptions.","key_machinery":"The load-bearing mechanism is a two-stage capture-and-survival chain. First, tidal stripping of a close-in giant leaves a debris ring whose gas spreads outward by viscous diffusion; the paper treats gas as captured by the outer planet if it enters a circle of radius R_cap = 0.2 R_Hill, an empirical scale from energy-balance considerations. Second, the captured envelope contracts on a Kelvin-Helmholtz timescale, with dust opacity setting the rate, and this contraction regulates further gas accretion. The surviving atmosphere is then eroded by XUV-driven escape and stellar wind, and its transit signal is estimated from the effective height of an isothermal hydrostatic envelope.","core_discovery":"The paper's central claim is that volatile-rich gas expelled when a close-in giant planet is tidally stripped can be re-accreted by a lower-mass outer planet, creating a 'volatile-enriched planet' (VEP) with a transient H/He envelope. In their 2D hydrodynamical simulations, a Jupiter-like planet disrupted near the Roche limit produces a viscous gas ring that spreads outward over a few years; a 1 or 10 Earth-mass planet placed at 0.04 or 0.07 au captures gas within 0.2 Hill radii. The captured envelope masses range from about 2.75 x $10^{-10}$ to 4.58 x $10^{-6}$ Earth masses, with the more massive planet capturing more gas and the less massive planet holding a more extended envelope. These envelopes yield transit depths of roughly 24 to 293 ppm and, under XUV-driven escape, persist for $10^{6}$ to $10^{8}$ years. The paper presents this as a viable pathway for the formation of volatile-rich, inflated low-mass planets, especially when accompanied by dynamical signatures such as eccentric orbits.","pith_inferences":["The 0.2-Hill-radius capture prescription is the assumption to test next; if the region from which gas truly remains bound is smaller, the quoted envelope masses and transit depths scale as the square of the radius ratio and could drop by orders of magnitude.","The scenario predicts that VEP atmospheres should be nearly pure hydrogen and helium even when the host star is metal-rich, so atmospheric metallicity measurements of warm sub-Neptunes could distinguish this pathway from other atmosphere origins.","A statistical correlation between moderate orbital eccentricity and H/He-rich, low-density envelopes among warm Neptune-mass planets would strengthen the case that these are remnants of disruptions."],"forward_implications":["Surviving low-mass planets in systems that host or hosted a close-in giant can acquire H/He atmospheres without forming in a gas-rich protoplanetary disk, extending atmosphere formation to evolved systems.","The captured envelopes outlast the debris disk by orders of magnitude: the gas disk disperses on a viscous timescale of about 160 years, while the atmospheres survive for 1 to 100 million years.","Transit depth depends strongly on planetary mass: 1 Earth-mass VEPs give roughly 180 to 293 ppm, while 10 Earth-mass VEPs give 24 to 35 ppm, making low-mass planets the best targets for detection.","Systems combining a metal-enriched star, an eccentric low-density planet, and an H/He-rich atmosphere, such as WASP-107b, HAT-P-11b, and TOI-421b, are consistent with a past disruption event.","An extended, asymmetric, or optically thick captured envelope can produce transit shapes that mimic rings or disks, potentially biasing radius and atmosphere measurements if ignored."],"supporting_citations":[{"why":"Supplies the empirical R_cap = 0.2 R_Hill capture radius used to define the accreted envelope mass.","marker":"Montesinos et al. 2025"},{"why":"Provides the model of viscous gas redistribution after tidal disruption, which drives the outward spread studied here.","marker":"Metzger et al. 2012"},{"why":"Gives the Kelvin-Helmholtz contraction timescale that sets the gas accretion rate onto the outer planet.","marker":"Ikoma et al. 2000"},{"why":"Supplies the XUV-driven escape and stellar-wind mass-loss formalism used to estimate atmospheric persistence timescales.","marker":"Alvarado-Montes et al. 2025"},{"why":"The FARGO3D code is the numerical engine for the 2D hydrodynamical simulations of gas diffusion and capture.","marker":"Benítez-Llambay & Masset 2016"},{"why":"Provides the transit-depth relation from effective atmospheric height used to convert envelope properties to observable signals.","marker":"de Wit & Seager 2013"},{"why":"The REBOUND package is used for the N-body and MEGNO dynamical stability calculations.","marker":"Rein & Liu 2012"},{"why":"Provides the three-layer internal structure model used to build the disrupted giant's atmosphere, envelope, and core density profiles.","marker":"Miguel et al. 2022"},{"why":"Supplies the Rosseland mean opacities used in the envelope contraction model.","marker":"Semenov et al. 2003"},{"why":"The ZTF SLRN-2020 candidate planetary-engulfment event is the observational motivation for studying the fate of disrupted giant planets.","marker":"Lau et al. 2025"}],"fun_headline_variants":["Gas giant's death can gift a sibling planet a volatile atmosphere","Shredded gas giant's volatile shroud may recreate an atmosphere","A tidal-disruption aftermath: new atmospheres for low-mass planets","Volatile hand-me-downs: how a shredded giant can cloak a sibling","Distant worlds may inherit atmospheres from a cannibalized gas giant"],"cache_read_input_tokens":13056,"weakest_assumption_plain":"The entire inventory of captured gas rests on treating every particle inside 0.2 Hill radii as accreted atmosphere, so if gas there is not actually bound to the planet, the quoted envelope masses and transit depths shrink dramatically.","fun_headline_variants_meta":{"raw":{"variants":["Gas giant's death can gift a sibling planet a volatile atmosphere","Shredded gas giant's volatile shroud may recreate an atmosphere","A tidal-disruption aftermath: new atmospheres for low-mass planets","Volatile hand-me-downs: how a shredded giant can cloak a sibling","Distant worlds may inherit atmospheres from a cannibalized gas giant"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00223,"raw_usage":{"total_tokens":8675,"prompt_tokens":1046,"completion_tokens":7629,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":662,"completion_tokens_details":{"reasoning_tokens":7536}},"tokens_in":662,"tokens_out":7629,"duration_ms":62006,"temperature":1.0,"reasoning_tokens":7536,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T17:05:21.425096+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Run a 3D hydrodynamical simulation that tracks whether gas entering the 0.2-Hill-radius zone remains gravitationally bound to the planet after the viscous disk disperses, or take a high-sensitivity transmission spectrum of a 1 to 10 Earth-mass planet at 0.04 to 0.07 au in a system with a recent giant disruption and check whether the predicted tens-to-hundreds of parts per million H/He signal is present.","supporting_citations":[{"cited_title":"2025, ApJ, 985, 36","cited_arxiv_id":null,"evidence_quote":"Supplies the empirical R_cap = 0.2 R_Hill capture radius used to define the accreted envelope mass."},{"cited_title":"2000, ApJ, 537, 1013","cited_arxiv_id":null,"evidence_quote":"Gives the Kelvin-Helmholtz contraction timescale that sets the gas accretion rate onto the outer planet."},{"cited_title":"A., Sucerquia, M., Zuluaga, J","cited_arxiv_id":null,"evidence_quote":"Supplies the XUV-driven escape and stellar-wind mass-loss formalism used to estimate atmospheric persistence timescales."},{"cited_title":"M., Jencson, J","cited_arxiv_id":null,"evidence_quote":"The ZTF SLRN-2020 candidate planetary-engulfment event is the observational motivation for studying the fate of disrupted giant planets."}],"review_version":1}