{"id":"c282443b-e95a-4ad8-b64a-877b280798e1","arxiv_id":"2608.03857","paper_version":2,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Across all simulated climates, Ross 128 b reflects only 0 to 20 percent of starlight, well below the commonly assumed 0.3, which would overestimate its detectability.","lead":"This paper simulates possible climates of Ross 128 b, a rocky exoplanet close to its M dwarf star, and computes how much light it reflects in the bandpasses of the upcoming RISTRETTO and ANDES instruments. Across all scenarios, the planet reflects far less light than the common Earth-like albedo assumption of 0.3, suggesting detection predictions for such planets should be revised.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The abstract's albedo ranges omit the surface-albedo assumption that the paper itself says dominates the result; the 0.3-overestimate conclusion is therefore scoped more narrowly than stated.","rationale":"The reader's conditional verdict is appropriate. The paper is unusually transparent, and its model outputs are internally consistent, so no rejection is warranted. The single most load-bearing soft spot is the unscoped generalization of the albedo values and the '0.3 overestimate' conclusion. The numeric ranges are anchored to A_surf = 0.2; because the transparent-atmosphere cases scale linearly with A_surf, plausible brighter rock surfaces would move the upper RISTRETTO albedo above the 0.3 benchmark. The paper flags this itself in Section 5, so the issue is not an omission but a presentation-and-robustness concern: the abstract states the ranges without the qualifier, and the population-level conclusion requires either a constraint on surface albedo or a conditional phrasing. The water-mass non-conservation in Section 3.1.3 is small (10^-3 %) and unlikely to affect the albedo claim. The haze caveat is real but secondary because the claim is explicitly scoped to hazeless planets; the surface albedo is not similarly excluded from the population statement. Hence the reader's conditional verdict should stand unchanged, with the abstract and conclusions tightened to carry the A_surf qualifier.","tokens_in":31205,"tokens_out":5979,"duration_ms":53034,"concrete_test":"Recompute the band-integrated geometric albedo for the transparent-atmosphere scenarios (Case 2 dry at 1 bar N2, Case 1 at 0.1 bar N2, and Case 2A) with Pytmosph3R using A_surf = 0.4 and 0.6 instead of 0.2, keeping all other inputs identical. If the RISTRETTO-band mean Ag exceeds 0.3 for A_surf = 0.6, the quoted ranges and the 0.3-overestimate conclusion are conditional on the assumed surface albedo and must be re-scoped or qualified in the abstract.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The strongest claim's quantitative content—geometric albedos of 0.07–0.2 (RISTRETTO) and 0–0.14 (ANDES)—is computed with a fixed surface albedo A_surf = 0.2 (Section 2.1, Table 2). For radiatively transparent atmospheres the geometric albedo approaches Ag = (2/3) A_surf for a Lambertian surface (Section 2.2.2), so the upper end of the RISTRETTO range is essentially set by Rayleigh scattering on top of this assumed dark surface. Section 5 explicitly concedes: 'these results are highly sensitive to the assumed surface albedo' and lists feldspathic, granitoid, and clay surfaces as plausible brighter alternatives. If A_surf = 0.4–0.6, the clear-atmosphere cases would yield Ag ≈ 0.27–0.40 in the visible, at or above the 0.3 Earth-like value the paper argues overestimates reflectivity. The haze caveat is partially covered by the word 'hazeless' in the abstract, but the surface-albedo dependence is an internal assumption, not an excluded process, and the abstract's ranges do not state it. Thus the central quantitative conclusion is not yet robust for the population as a whole without a constraint on the distribution of surface albedos.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper uses the Generic-PCM 3D global climate model to simulate a broad suite of climate states for Ross 128 b, varying atmospheric composition (N2, N2+CO2, CO2), surface pressure (0.1-10 bar), water inventory (dry to 83.3 cm GEL), and spin-orbit resonance (1:1 and 5:2). The GCM outputs are post-processed with Pytmosph3R to produce synthetic reflectance spectra and mean Bond and geometric albedos in the RISTRETTO and ANDES bandpasses. The authors identify collapsed, transient, and runaway climate states, find geometric albedos of 0.07-0.2 in the RISTRETTO bandpass and 0-0.14 in the ANDES bandpass across all scenarios, and argue that the common 0.3 Earth-like albedo assumption likely overestimates reflectivity for this planet population.","tokens_in":31525,"tokens_out":4992,"duration_ms":42370,"significance":"If the low-albedo result is robust, it directly affects the predicted contrast ratios and exposure times for reflected-light characterization of non-transiting rocky planets with RISTRETTO, ANDES, and PCS, and it provides a useful alternative to the ad hoc 0.3 albedo assumption commonly used in observability studies. The paper is transparent about many of its limitations, publishes the GCM outputs on Zenodo, and grounds the climate bistability in earlier work rather than assuming it. The main weakness is that the headline albedo ranges are computed for a fixed surface albedo of 0.2, and the authors themselves state in Section 5 that the results are highly sensitive to this assumption; the abstract and conclusions do not carry this caveat forward.","major_comments":[{"comment":"The abstract and Section 4.3 state, as a population-level result, that \"hazeless rocky planets receiving stellar irradiations similar to Ross 128 b exhibit rather low reflectivity, with geometric albedos ranging from 0.07 to 0.2 in the RISTRETTO bandpass and from 0 to 0.14 in the ANDES bandpass across all simulated scenarios,\" and conclude that the 0.3 Earth-like value overestimates reflectivity. These statements omit the fact that every simulation assumes a surface albedo of A_surf = 0.2 (Section 2.1, Table 2). As Section 2.2.2 notes, a Lambertian surface alone gives A_g = 2/3 A_surf; hence the upper end of the quoted RISTRETTO range is set by the assumed dark surface plus Rayleigh scattering. Section 5 concedes that \"these results are highly sensitive to the assumed surface albedo\" and lists feldspathic, granitoid, and clay surfaces as plausible brighter alternatives; with A_surf = 0.4-0.6 the clear-atmosphere geometric albedo would reach 0.27-0.40, at or above the 0.3 value the paper argues is an overestimate. The central population-level conclusion is therefore scoped more narrowly than the abstract and conclusions suggest. Please qualify the abstract and conclusions with the A_surf = 0.2 assumption, or add a sensitivity analysis (e.g., recompute clear-atmosphere and thin-atmosphere geometric albedos for A_surf = 0.3-0.6) to determine the range of surface albedos over which the low-albedo conclusion holds.","section":"Abstract; Sections 4.3 and 5"}],"minor_comments":[{"comment":"The footnote reporting a 10^-3% non-conservation of global water mass is important for reproducibility; please move this information into the main text or appendix with a brief explanation of the likely cause, since the transient state (Case 2B) is a central result.","section":"Section 3.1.3, footnote 1"},{"comment":"The \"dry\" scenarios still include a residual water amount in the correlated-k tables, which leaves trace water features in the spectra (footnote 3 of Section 4.2.2). Please state quantitatively how much residual water is present and how it affects the reported albedo values, so that readers do not interpret the dry cases as strictly water-free.","section":"Sections 2.1.3 and 4.2.2"},{"comment":"The color scales differ between panels in several multi-panel maps, which makes cross-case comparison difficult; consider using unified color scales or explicitly labeling the color-bar limits in each panel.","section":"Figures 3, 4, and 5"},{"comment":"The text mentions both the lower spectral resolution of the GCM correlated-k tables (58/28 bands) and the higher resolution used by Pytmosph3R (R=300 or 500); please clarify the distinction between these two resolutions to avoid confusion about the fidelity of the synthetic spectra.","section":"Section 2.2.1"},{"comment":"There are a few typographical errors, including \"Institut Poytechnique\" in the affiliations and \"https://svn.lmd.jussieu.fr/Planeto/\" in the Data availability section; these should be corrected before publication.","section":"Title page and Data availability"}],"recommendation":"major_revision","confidential_remarks":"The paper is a good fit for A&A and the modeling effort is substantial and well documented. The main concern for me is that the headline claim in the abstract and conclusions is broader than what the simulations actually support, given the fixed surface albedo. The authors already acknowledge this in Section 5, so the fix could be as simple as re-scoping the abstract and conclusions; a short sensitivity test for A_surf would make the claim considerably stronger. I would not reject the paper on this basis, but I do think the central claim needs this qualification before it is suitable for publication."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The one thing you should know: this is a solid, useful grid of geometric albedo values for Ross 128 b-like planets, and it makes a good case that the default 0.3 Earth-like albedo is too high for hazeless, low-water planets at this irradiation. But the quantitative ranges in the abstract are narrower than the assumptions that produced them.\n\nWhat's actually new is the systematic sweep: water inventories from 0 to 83 cm GEL, N2 and CO2 atmospheres, 0.1 to 10 bar, synchronous and 5:2 resonance, with bandpass-averaged geometric albedos for RISTRETTO and ANDES computed consistently from GCM and radiative transfer. The climate bistability itself is reproduced from Leconte et al. 2013 and Chaverot et al. 2023, not claimed as new. That's fair. The observability-oriented synthesis—which instrument bandpasses see what, how clouds shift to the nightside, how Rayleigh scattering boosts the visible—is genuinely useful for target selection.\n\nThe main soft spot is exactly where the stress-test points: everything rests on A_surf = 0.2. For an optically thin atmosphere, Ag approaches 2/3 of A_surf, so the upper end of the RISTRETTO range (0.2) is essentially that chosen surface, not a prediction. Section 5 says the results are 'highly sensitive to the assumed surface albedo,' and then lists feldspathic and clay surfaces as plausible brighter alternatives. The abstract says 'hazeless' but does not say 'for A_surf=0.2,' which overstates the scope of the conclusion. That is fixable with either a sensitivity scan or a one-sentence caveat.\n\nThe water mass non-conservation (10^-3%) is a real but minor bug, and they flagged it. The dry-scenario residual water is also minor. The paper is transparent, the code and data are available, and the citations are to the right prior work. No circularity.\n\nWho this is for: anyone planning reflected-light observations with RISTRETTO/ANDES/PCS, and anyone doing climate-to-observable modeling of hot rocky planets.\n\nRecommendation: send it to peer review. The central mechanism is sound; it just needs the surface-albedo caveat in the abstract and ideally a short sensitivity test in Section 5.","headline":"A genuinely useful albedo grid for Ross 128 b-like planets, but the headline low-albedo ranges silently depend on the assumed dark surface.","tokens_in":32037,"tokens_out":1994,"would_cite":true,"duration_ms":17779,"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":"Close-in rocky exoplanets around M dwarfs are likely much darker than the standard 0.3 Earth-like albedo used in detection forecasts.","keywords":["Ross 128 b","geometric albedo","reflected-light spectroscopy","tidally locked exoplanets","moist bistability","terrestrial exoplanet atmospheres","high-contrast imaging","M dwarf habitable zone"],"falsifier":"Measure the reflected-light phase curve of Ross 128 b with PCS: a band-integrated geometric albedo above 0.2 in the 0.62 to 0.84 micron RISTRETTO band, or a near-infrared spectrum showing cloud or haze scattering instead of saturated water-vapor absorption, would rule out the paper's low-albedo conclusion for this population.","tokens_in":31037,"feed_emoji":"🔭","tokens_out":9182,"duration_ms":71407,"temperature":0.7,"pith_summary":"The paper claims that warm, close-in rocky exoplanets around M dwarfs probably reflect much less starlight than the 0.3 Earth-like value routinely used in detection forecasts. Using Ross 128 b as a prototype, it couples three-dimensional climate simulations across many atmospheric compositions, pressures, water inventories, and spin states with synthetic reflectance spectra for the RISTRETTO and ANDES bandpasses. Across every simulated scenario, the geometric albedo stays between 0.07 and 0.2 in the visible RISTRETTO band and between 0 and 0.14 in the near-infrared ANDES bands. If true, this means planning observations on the assumption of 0.3 reflectivity would overestimate planet-to-star contrast, and darker targets may need longer exposures or may be missed entirely.","feed_headline":"Close-in rocky planets are darker than the usual 0.3 albedo","feed_subtitle":"Ross 128 b models put visible geometric albedo at 0.07-0.2 and near-infrared at 0-0.14, dimming detection forecasts.","key_machinery":"The carrying mechanism is the climate moist bistability of close-in, low-water-reservoir rocky planets: for the same star and orbit, the climate can settle into either a collapsed state with water frozen out on the nightside and a cloud-free dayside, or a runaway state with all water vaporized, with a narrow transient state between them. Because cloud formation occurs almost exclusively on the nightside in these regimes, the dayside that observers see lacks reflective clouds and ice, so the geometric albedo is controlled by the surface albedo, Rayleigh scattering by the atmospheric gas, and water vapor and carbon dioxide absorption in the near-infrared. The paper couples this climate output to a radiative-transfer computation of phase-dependent reflected-light spectra to convert each simulated climate into a wavelength-dependent geometric albedo in the instrument bandpasses.","core_discovery":"The central claim is that the reflectivity of close-in, non-transiting rocky planets is set by climate, not by an arbitrary Earth-like constant, and that for Ross 128 b-like irradiation the climate almost always acts to lower albedo. The 3D climate simulations produce two stable end states characteristic of moist bistability: a collapsed state where water is trapped as nightside surface ice and the dayside atmosphere is dry and cloud-free, and a runaway state where all water is vaporized and its strong near-infrared absorption darkens the planet, with a transient state of localized nightside liquid water between them. In all cases, dayside cloud decks and dayside ice are absent, so visible reflectivity stays close to the assumed dark rocky surface, while water vapor and carbon dioxide absorb most of the near-infrared flux. The resulting geometric albedo ranges are 0.07 to 0.2 in the RISTRETTO band and 0 to 0.14 in the ANDES YJH bands, with dense nitrogen or carbon dioxide atmospheres raising the visible albedo through Rayleigh scattering and water-rich runaway states driving it toward zero in the near-infrared.","pith_inferences":["If real planetary surfaces turn out to be brighter than the assumed 0.2 albedo, for example feldspathic, clay-like, or covered by photochemical hazes, the quoted albedo ranges would rise, so measuring surface mineralogy or haze refractive indices is the fastest way to tighten these forecasts.","A null or very dark detection of Ross 128 b by PCS would corroborate the low-albedo picture, whereas a visible-band geometric albedo above 0.2 would point to missing reflectors such as dayside clouds or hazes.","The paper's Case 2B water budget shows a small non-conservation of total water mass, of order 10^-3%, which the authors flag as needing investigation; the transient-state statistics rest on this approximation, even though the albedo impact is likely negligible.","The same modeling chain could be run for less irradiated targets where dayside cloud formation is expected; the albedo suppression found here should not be assumed for planets near the outer part of the habitable zone."],"forward_implications":["Detection-limit charts that assume a 0.3 geometric albedo overstate the reflected-light contrast of Ross 128 b-like planets; using the simulated albedos lowers predicted contrast and lengthens required exposure times for RISTRETTO, ANDES, and PCS.","The visible RISTRETTO bandpass mainly reports atmospheric density through Rayleigh scattering, while the ANDES near-infrared bands mainly report water vapor and carbon dioxide absorption, so combining both bands can distinguish a thick transparent atmosphere from a water-rich runaway atmosphere.","Even a planet inside the inner edge of the habitable zone can host localized liquid water in nightside cold traps for a narrow range of water inventory, so the climate state is not a monotonic function of irradiation alone.","Runaway states occur even at modest water inventories, with a transition around 8 cm of global equivalent layer, implying that highly irradiated rocky planets with small water reservoirs may commonly be dark in the near-infrared."],"supporting_citations":[{"why":"Defines the collapsed and runaway moist-bistability states and the circulation regime used to interpret the GCM results.","marker":"Leconte et al. 2013b"},{"why":"Provides the GCM methodology for close-in M-dwarf rocky planets and the CO2 atmospheric-collapse feedback used for the thin CO2 case.","marker":"Turbet et al. 2016"},{"why":"Shows that water clouds form on the nightside of water-rich tidally locked planets, justifying the absence of reflective dayside clouds.","marker":"Turbet et al. 2021"},{"why":"Quantifies nightside cloud warming and low Bond albedo for water-rich land planets, supporting the low-albedo interpretation.","marker":"Chaverot et al. 2023"},{"why":"Documents reflective dayside clouds for somewhat less irradiated synchronous planets, the contrast case the paper argues does not apply at Ross 128 b irradiation.","marker":"Yang et al. 2013"},{"why":"Supplies the habitable-zone inner-edge limit and runaway-greenhouse criterion placing Ross 128 b interior to the inner edge.","marker":"Kopparapu et al. 2017"},{"why":"Provides the 5:2 spin-orbit resonance, eccentricity, and obliquity used for the asynchronous-rotation scenarios.","marker":"Valente & Correia 2022"},{"why":"Discovery paper supplying Ross 128 b's orbital period, semi-major axis, and projected mass used to set up simulations.","marker":"Bonfils et al. 2018"},{"why":"Source of the common 0.3 Earth-like geometric albedo assumption that the paper's estimates are compared against.","marker":"Madden & Kaltenegger 2018"}],"fun_headline_variants":["Ross 128 b: albedo 0.07–0.2, not 0.3","Climate drives albedo, as seen on Ross 128 b","Close-in rocky worlds are darker than assumed","Moist bistability suppresses reflectivity on Ross 128 b","Rocky exoplanet albedo: 0.07–0.2, not Earth-like"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The low albedo range rests on assuming a dark rocky surface with albedo 0.2 and omitting photochemical hazes and dayside clouds; if real surfaces are brighter or hazes form, the reflectivity could be substantially higher.","fun_headline_variants_meta":{"raw":{"variants":["Ross 128 b: albedo 0.07–0.2, not 0.3","Climate drives albedo, as seen on Ross 128 b","Close-in rocky worlds are darker than assumed","Moist bistability suppresses reflectivity on Ross 128 b","Rocky exoplanet albedo: 0.07–0.2, not Earth-like"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000417,"raw_usage":{"total_tokens":2250,"prompt_tokens":1142,"completion_tokens":1108,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":758,"completion_tokens_details":{"reasoning_tokens":1009}},"tokens_in":758,"tokens_out":1108,"duration_ms":9223,"temperature":1.0,"reasoning_tokens":1009,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T04:13:11.719866+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the reflected-light phase curve of Ross 128 b with PCS: a band-integrated geometric albedo above 0.2 in the 0.62 to 0.84 micron RISTRETTO band, or a near-infrared spectrum showing cloud or haze scattering instead of saturated water-vapor absorption, would rule out the paper's low-albedo conclusion for this population.","supporting_citations":[],"review_version":2}