{"id":"0b50a080-3b42-4f04-9faf-1283a8139df1","arxiv_id":"2506.02188","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"LP 791-18d's outgassed atmosphere is stable only for highly oxidized interiors (fO2-IW greater than about 2); reduced interiors lose their volatiles to hydrodynamic escape within the planet's lifetime.","lead":"This paper models the atmosphere of the volcanic rocky exoplanet LP 791-18d, linking the planet's interior oxidation state to whether its atmosphere survives. It finds that only strongly oxidized interiors can keep a stable atmosphere, and proposes a three-color JWST observation scheme to tell bare rock from a real atmosphere.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The stability threshold fO2-IW >~2 rests on an underdetermined escape closure: Section 5 claims T0 is solved from Eqs. (14)-(20), but Eq. (20) contains no T0, leaving r_s and the wind/stable boundary unconstrained.","rationale":"The paper's core contribution is a coupled interior-atmosphere model with a sharp prediction: reduced interiors (fO2-IW <~2) lose their secondary atmospheres to hydrodynamic escape, while oxidized ones persist. The stability analysis in Section 5 is therefore the load-bearing pillar. The weakest step is the escape closure. As written, Eq. (20) gives Mdot but no T0; without T0, Eq. (17) cannot yield r_s, and the criterion r_s <= R_exo is indeterminate. The paper even offers two inconsistent descriptions of how T0 is set (solved from 'the system of equations' in Sec. 5, versus the peak temperature of the thermal profile in Sec. 8). This is not merely a presentation issue: because the authors concede the isothermal treatment yields only upper-bound mass-loss rates, a self-consistent thermosphere with radiative cooling would lower T0 and reduce escape, potentially stabilizing reduced atmospheres and shifting the redox threshold. The proposed variable-T0 test would settle whether the threshold is robust. The verdict remains CONDITIONAL: the qualitative framework and the color-color diagnostic are valuable and testable, but the central stability claim is not yet uniquely determined by the equations presented. The reader's weakest_assumption identified exactly this point, so agreement is 'agree'.","tokens_in":30689,"tokens_out":6971,"duration_ms":64055,"concrete_test":"Take a representative reduced case (e.g., fO2-IW = 0, P_s = 1 bar, a_C = 1e-6) and recompute the Section 5 stability classification while varying the isothermal wind temperature T0 over a physically plausible range (approximately 200-2000 K). For each T0, compute r_s from Eq. (17) and compare with the exobase radius; if the case switches from 'wind regime' to 'stable thermosphere' across that T0 range, then the wind/stable boundary in Figure 8 is not fixed by the stated equations. This directly tests whether the fO2 ~ 2 threshold is an artifact of the missing T0 closure.","verdict_should_be":"UNCHANGED","load_bearing_attack":"In Section 5, the planetary-wind classification is governed by whether the isothermal sonic radius r_s = GM_p/(2 v_s^2) (Eq. 17) lies below the exobase, with v_s = sqrt(k T0/(mu m_H)) (Eq. 16). The paper states that 'closure' for T0 is achieved via the energy-limited mass-loss formula (Eq. 20): Mdot = eta pi F_XUV R_xuv^3/(G M_p). This equation contains neither T0 nor a base density, so on its own it does not determine v_s, r_s, or the density profile. Section 8 then offers a different description (T0 'captures the peak temperature of the thermal profile' near the wind base), which is not derived from the Section 5 system. If T0 is instead taken from the model's own thermospheric peak, the stability boundary becomes sensitive to that choice; if it is to be solved from the stated system, an additional matching condition is missing. The central claim that stability requires fO2-IW >~2 depends directly on r_s. A lower T0 (consistent with the radiative cooling the authors concede would reduce escape) moves r_s outward, expanding the stable region toward reduced compositions. Because the 10^5-10^8 kg/s mass-loss rates and the resulting volatile-exhaustion argument (Eq. 34) are themselves labeled 'qualitative upper bounds', the threshold could shift below fO2 ~ 0, undermining the abstract's headline conclusion.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper presents a coupled modeling study of the tidally heated rocky exoplanet LP 791-18 d, combining an interior outgassing model (Tian & Heng 2024), chemical kinetics and photochemistry (VULCAN), radiative-convective transfer (HELIOS), and synthetic secondary-eclipse spectra. The authors estimate a mantle temperature of ~1680-1880 K from fluid tidal heating, compute steady-state atmospheric compositions over a grid of oxygen fugacity, surface pressure, and graphite activity, and then classify each atmosphere as stable or as undergoing hydrodynamic escape using an isothermal planetary-wind criterion. The central claims are that the atmospheric mean molecular weight is controlled by oxygen fugacity rather than bulk metallicity, that stable atmospheres require highly oxidized interiors (fO2-IW ≳ 2), that reduced interiors suffer mass loss of order 10^5-10^8 kg/s and likely exhaust their volatiles, and that a three-band JWST/MIRI color-color diagram can distinguish bare-rock surfaces from thick oxidized atmospheres.","tokens_in":30996,"tokens_out":4582,"duration_ms":46841,"significance":"If the stability threshold fO2-IW ≳ 2 holds, the paper would establish a direct connection between interior redox state and the survivability of secondary atmospheres on M-dwarf rocky planets, with clear observational predictions for LP 791-18 d and similar targets. The study is valuable for its integration of outgassing, photochemistry, radiative transfer, and observing-strategy analysis in a single framework, and it explicitly labels its escape rates as qualitative upper bounds. The color-color diagnostic is a useful new idea, and the comparison of HELIOS and petitRADTRANS spectra is a welcome validation step. The central results are model outputs rather than fitted targets, so the circularity burden is low; the main risks are the technical closure of the escape model and the strength of a claim that is not actually varied in the parameter grid.","major_comments":[{"comment":"The closure for T0 is not specified in the text. Eq. (20) gives an energy-limited mass-loss rate that contains neither T0 nor a base density, so on its own it does not determine the isothermal sonic speed v_s, the sonic radius r_s = GM_p/(2 v_s^2), or the stable-versus-wind boundary. One can close the system if the simulated density at R_xuv is used in Eq. (14) together with Eqs. (18)-(19), but this step is never stated. Section 8 introduces a different prescription, that T0 'captures the peak temperature of the thermal profile' near the wind base, which is not derived from the §5 system. Since the headline threshold fO2-IW ≳ 2 depends directly on r_s, please state the closure explicitly, show how T0 is obtained, and test the sensitivity of the stability boundary to the adopted T0 or to the thermospheric peak temperature.","section":"§5, Eqs. (14)-(20)"},{"comment":"The claim that the atmospheric mean molecular weight is controlled by oxygen fugacity 'rather than bulk metallicity' is not tested by the simulations. The grid varies oxygen fugacity, surface pressure, and graphite activity, but no independent bulk-metallicity axis is varied. Either add simulations that vary the total volatile inventory or bulk metallicity, or restate the conclusion as dominance of fO2 over the other varied parameters. As written, the abstract overstates what the parameter space can show.","section":"Abstract and §4.3, Table 1"},{"comment":"The volatile-exhaustion argument uses the mass-loss rates that the paper itself labels as 'qualitative upper bounds' because radiative cooling is neglected. At the lower bound of 10^5 kg/s, the cumulative loss over 500 Myr is ~1.6×10^21 kg, which is below the adopted conservative reservoir of ~6×10^21 kg; a reduction of the escape rate by a factor of a few, as expected from radiative cooling, would remove the conclusion that reduced interiors are 'likely exhausted'. Please propagate the stated uncertainty in Mdot into the lifetime estimate and either quantify a lower bound on the escape rate or soften the abstract and concluding claims accordingly.","section":"§8, Eq. (34)"}],"minor_comments":[{"comment":"The text describes R_xuv as the deposition radius, but the equation's variable list mentions R_p; please make the notation consistent.","section":"§5, Eq. (20)"},{"comment":"The text mentions a species-specific correction factor Γ_ij, but the equation as printed does not include Γ_ij; please clarify where the correction enters.","section":"§4.1, Eq. (6)"},{"comment":"The dashes in the grid could mean either 'not computed' or 'did not converge'; please state which.","section":"Table 1"},{"comment":"The legend for the convective flux curves with different melt-fraction coefficients B is hard to read; please make the curve labels explicit in the figure.","section":"Fig. 2"},{"comment":"The phrase 'energy-limited constant flow' is misleading because Eq. (20) is an integrated energy budget, not a flow closure; consider renaming it as an energy-limited mass-loss constraint.","section":"§5"},{"comment":"The citation to Drant et al. (2025) as 'in minor revision' should be updated to the published version or marked as submitted.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The paper is potentially publishable after the escape-model closure is made explicit and the metallicity and volatile-exhaustion claims are appropriately qualified. The central threshold may survive, but as written the underdetermined closure of Eqs. (14)-(20) is a load-bearing gap that a careful reader cannot fill without additional assumptions."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The short version: this is a worthwhile modeling paper. The new pieces are a coupled interior-outgassing–atmosphere grid for LP 791-18d and a three-band F1000W/F1500W/F2100W color–color diagram that separates stable oxidized atmospheres from bare-rock scenarios. But the headline stability threshold (fO2-IW ≳ 2) is less certain than the abstract implies, and one abstract claim—'controlled by oxygen fugacity rather than bulk metallicity'—isn't actually tested.\n\nWhat I like: the authors do real work. They update the tidal heating estimate using the fluid-tide model (Farhat et al. 2025), which pushes the mantle temperature to 1680–1880 K, and they couple VULCAN/HELIOS with a lower-boundary outgassing scheme across a redox–pressure grid. They check sensitivity to albedo, graphite activity, hazes, and gray clouds. The three-band diagram is a concrete advance over Hammond et al.'s two-band degeneracy discussion. And in Section 8 they are appropriately honest that the mass-loss rates are qualitative upper bounds and that a full upper-atmosphere treatment is needed.\n\nThe soft spots, in order of importance. First, the escape closure. Section 5 says the isothermal wind temperature T0 is solved using the energy-limited formula (Eq. 20), but that formula contains no T0. The sonic radius, and therefore the wind/stable boundary, is not uniquely determined from the stated system. Section 8 later implies T0 is the peak temperature of the thermal profile near the wind base—a different statement. This matters because the stability threshold depends directly on r_s; a cooler thermosphere would move the boundary toward more reduced compositions. The qualitative direction—reduced interiors lose light atmospheres faster—survives, but the abstract's crisp 'stability only at fO2-IW ≳ 2' overstates the precision. Second, the 'rather than bulk metallicity' claim is unsupported: bulk metallicity is not varied in the grid. It should be softened or tested. Third, the central coupling code is unpublished (Drant et al. 2025, in minor revision). A public version would strengthen the reproducibility.\n\nWho this is for: people planning JWST observations of temperate rocky planets around M dwarfs, and modelers working on interior–atmosphere coupling. I'd send it to a serious referee. The referee should ask for a clear statement of how T0 is set, a softening of the metallicity claim, and ideally a public coupling code. With those changes, it's a solid contribution.","headline":"Useful case study with a novel three-band diagnostic, but the stability threshold is less certain than the abstract implies.","tokens_in":31604,"tokens_out":3862,"would_cite":true,"duration_ms":35439,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"The interior oxidation state decides whether an outgassed rocky planet retains its atmosphere.","keywords":["LP 791-18 d","secondary atmospheres","outgassing","oxygen fugacity","hydrodynamic escape","JWST/MIRI photometry","color-color diagram","tidal heating"],"falsifier":"If JWST/MIRI observations of LP 791-18 d detect a CO2-rich atmosphere under conditions where the interior is inferred to be reduced ($f_{O_2}-\\mathrm{IW}$ below about 2), or if a non-isothermal upper-atmosphere model including radiative cooling finds stable thermospheres for reduced compositions, the paper's central claim would be contradicted.","tokens_in":30459,"feed_emoji":"🌋","tokens_out":7781,"duration_ms":74664,"temperature":0.7,"pith_summary":"This paper tries to establish that on tidally heated, volcanically outgassing rocky planets like LP 791-18 d, the interior's oxidation state, not its bulk metallicity, decides whether a secondary atmosphere can survive. Using a coupled model of mantle outgassing, photochemistry, and escape, the authors find that only strongly oxidized interiors (oxygen fugacity about two orders of magnitude above the iron–wüstite buffer) yield atmospheres heavy enough to resist hydrodynamic escape. Reduced interiors lose mass at roughly $10^{5}$ to $10^{8}$ kg/s and would likely exhaust their volatile budget within the system's roughly 500 million year lifetime. The paper also proposes a three-band JWST color–color diagram that separates surviving atmospheres from bare-rock surfaces even when hazes and clouds are present. If correct, atmospheric detections around small M-dwarf planets would preferentially point to oxidized interiors, and bare or tenuous surfaces should be common.","feed_headline":"Only oxidized rocky interiors can keep secondary atmospheres","feed_subtitle":"On LP 791-18 d, reduced envelopes blow away while oxidized ones survive; three JWST bands tell survivors from bare rock.","key_machinery":"The controlling mechanism is the mean molecular weight at the XUV-deposition layer, which fixes the isothermal sound speed $v_s = \\sqrt{k T_0/(\\mu m_H)}$ and therefore the sonic radius $r_s = G M_p/(2 v_s^2)$. The paper classifies an atmosphere as unstable when this sonic radius lies below the exobase, so a hydrodynamic wind forms; when it lies above, the thermosphere is treated as stable. Because oxygen fugacity determines which molecules the magma outgasses, light H$_2$/CH$_4$-rich compositions under reducing conditions versus heavier CO$_2$/H$_2$O-rich compositions when oxidized, the interior redox state effectively chooses the escape regime. The modeling chain couples a Gibbs-energy melt–gas equilibrium at the lower boundary, 1D radiative–convective and photochemical-kinetic steady states, and an isothermal wind solution closed by the energy-limited mass-loss formula.","core_discovery":"The paper's central claim is that atmospheric stability on outgassing rocky exoplanets is controlled by the interior redox state: stability is achieved only for highly oxidized scenarios, roughly $f_{O_2}-\\mathrm{IW} \\gtrsim 2$, while reduced interior states fall into the hydrodynamic escape regime with mass-loss rates on the order of $10^5$–$10^8$ kg/s. The authors further find that the mean molecular weight gradient of the outgassed atmosphere is set by oxygen fugacity rather than bulk metallicity, and that the atmosphere's survivability follows from that gradient because it sets the sound speed at the XUV-heated wind base. For the specific case of LP 791-18 d, they estimate a mantle temperature of about 1680–1880 K from fluid tidal heating, outgassing rates of roughly 20–27 km$^3$/yr of magma, and conclude that reduced-interior scenarios would have exhausted their volatiles over the planet's lifetime. They also predict that a color–color diagram using JWST/MIRI F1000W, F1500W, and F2100W photometry breaks the degeneracy between bare rock and thick atmospheres, with the separation robust to surface pressure, graphite activity, photochemical hazes, and gray clouds.","pith_inferences":["If the $f_{O_2}-\\mathrm{IW} \\gtrsim 2$ threshold holds generally, the population of rocky planets around M dwarfs with detectable atmospheres should be systematically oxidized, which would bias any census of volatile inventories and habitability indicators.","The same three-band color–color strategy could be applied to other JWST-observed rocky planets like TRAPPIST-1 b; if a bare-rock planet fell in the stable-atmosphere region of the diagram, the classification would need revision.","The intermediate redox range $0 \\lesssim f_{O_2}-\\mathrm{IW} \\lesssim 2$ may self-stabilize through preferential escape of light species and diffusive enrichment of heavy ones, a feedback the paper mentions but does not model; time-dependent escape–outgassing models could test whether such atmospheres survive longer than the static criterion predicts.","Because outgassed pressure scales exponentially with melt temperature, the mantle temperature of 1680–1880 K, derived from fluid tidal heating, is a sensitive input; a lower temperature would reduce outgassing and could shift the redox threshold, so pinning down the rheological transition is critical."],"forward_implications":["Reduced interiors ($f_{O_2}-\\mathrm{IW} \\lesssim 2$) are unlikely to retain secondary atmospheres over gigayear timescales; such planets should appear as bare or tenuous rocky worlds.","Atmospheric detections on small, tidally heated planets around M dwarfs would preferentially indicate oxidized interiors, making the observed sample biased toward high oxygen fugacity.","The color–color diagram with F1000W, F1500W, and F2100W can resolve the bare-rock versus thick-atmosphere degeneracy at roughly 30–45 ppm uncertainty, which is within JWST/MIRI reach for thin, highly oxidized atmospheres.","A single 15 µm band, or even two bands, cannot unambiguously separate an atmosphere from a bare rock; only the three-band combination does, and it is insensitive to surface pressure and graphite activity.","Mean molecular weight of the atmosphere tracks $\\log(f_{O_2})$, so emission spectra can be used to infer the planet's interior oxidation state."],"supporting_citations":[{"why":"Supplies the LP 791-18 system parameters, planet discovery, and the baseline solid-mantle tidal heating model that this work extends with fluid tides.","marker":"Peterson et al. (2023)"},{"why":"Provides the fluid tidal heating model that shifts the mantle equilibrium temperature up to 1680–1880 K, controlling the outgassing temperature.","marker":"Farhat et al. (2025)"},{"why":"Supplies the melt–gas equilibrium outgassing model that converts oxygen fugacity, surface pressure, and graphite activity into the initial atmospheric composition.","marker":"Tian & Heng (2024)"},{"why":"Provides the VULCAN chemical kinetics and photochemistry code used to reach steady-state atmospheric compositions.","marker":"Tsai et al. (2017)"},{"why":"Provides the HELIOS radiative-convective code that computes the atmospheric thermal structure coupled with chemistry.","marker":"Malik et al. (2017)"},{"why":"Gives the analytic heat-redistribution factor used to set the dayside temperature across the wide range of atmospheric mean molecular weights.","marker":"Koll (2022)"},{"why":"Supplies the energy-limited mass-loss formula used to close the isothermal wind model and compute escape rates.","marker":"Sanz-Forcada et al. (2011)"},{"why":"Provides the M-dwarf XUV luminosity evolution used to set the incident XUV flux and the system age for the escape calculation.","marker":"Johnstone et al. (2021)"},{"why":"Defines the planned JWST Cycle 3 observations of LP 791-18 d whose uncertainty budget the detectability analysis adopts.","marker":"Benneke et al. (2024)"},{"why":"Establishes the bare-rock versus thick-atmosphere photometric degeneracy that the paper's three-band color–color diagram aims to break.","marker":"Hammond et al. (2025)"}],"fun_headline_variants":["Redox state decides if rocky exoplanets keep atmospheres","Only oxidized rocky interiors retain secondary atmospheres","Reduced interiors blow atmospheres away on LP 791-18 d","Oxygen fugacity controls atmosphere survival on LP 791-18 d","Color-color diagram can spot hidden atmospheres on rocky worlds"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The whole stability verdict rests on an isothermal wind model whose closure equation does not actually fix the wind temperature, so the $f_{O_2}$ threshold near 2 is approximate and could shift if radiative cooling in the thermosphere is included.","fun_headline_variants_meta":{"raw":{"variants":["Redox state decides if rocky exoplanets keep atmospheres","Only oxidized rocky interiors retain secondary atmospheres","Reduced interiors blow atmospheres away on LP 791-18 d","Oxygen fugacity controls atmosphere survival on LP 791-18 d","Color-color diagram can spot hidden atmospheres on rocky worlds"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00022,"raw_usage":{"total_tokens":1534,"prompt_tokens":1121,"completion_tokens":413,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":737,"completion_tokens_details":{"reasoning_tokens":328}},"tokens_in":737,"tokens_out":413,"duration_ms":4097,"temperature":1.0,"reasoning_tokens":328,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T11:29:28.592429+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"If JWST/MIRI observations of LP 791-18 d detect a CO2-rich atmosphere under conditions where the interior is inferred to be reduced ($f_{O_2}-\\mathrm{IW}$ below about 2), or if a non-isothermal upper-atmosphere model including radiative cooling finds stable thermospheres for reduced compositions, the paper's central claim would be contradicted.","supporting_citations":[{"cited_title":"2025, ApJ, 979, 133","cited_arxiv_id":null,"evidence_quote":"Provides the fluid tidal heating model that shifts the mantle equilibrium temperature up to 1680–1880 K, controlling the outgassing temperature."},{"cited_title":"& Heng, K","cited_arxiv_id":null,"evidence_quote":"Supplies the melt–gas equilibrium outgassing model that converts oxygen fugacity, surface pressure, and graphite activity into the initial atmospheric composition."},{"cited_title":"R., Grosheintz, L., et al","cited_arxiv_id":null,"evidence_quote":"Provides the VULCAN chemical kinetics and photochemistry code used to reach steady-state atmospheric compositions."},{"cited_title":"M., et al","cited_arxiv_id":null,"evidence_quote":"Provides the HELIOS radiative-convective code that computes the atmospheric thermal structure coupled with chemistry."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Gives the analytic heat-redistribution factor used to set the dayside temperature across the wide range of atmospheric mean molecular weights."},{"cited_title":"P., Bartel, M., & Güdel, M","cited_arxiv_id":null,"evidence_quote":"Provides the M-dwarf XUV luminosity evolution used to set the incident XUV flux and the system age for the escape calculation."},{"cited_title":"M., Lichtenberg, T., et al","cited_arxiv_id":null,"evidence_quote":"Establishes the bare-rock versus thick-atmosphere photometric degeneracy that the paper's three-band color–color diagram aims to break."}],"review_version":1}