{"id":"9290df8e-2f69-4b55-b1f3-fa3147ea1814","arxiv_id":"2507.07165","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"The first NIRSpec G395H transmission spectrum of GJ 357 b is featureless, ruling out low mean molecular weight atmospheres at 3-sigma and pointing to a bare rock or a high molecular weight secondary atmosphere.","lead":"JWST observations of the super-Earth GJ 357 b show a flat transmission spectrum with no atmospheric features, ruling out hydrogen-rich atmospheres lighter than about 8 grams per mole and metallicities below 300 times solar. The planet is likely either a bare rock or a world with a heavy, high-molecular-weight atmosphere, and upcoming thermal emission data could distinguish the two.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 3-sigma MMW and metallicity exclusions hinge on the assumption of a strictly constant NRS1-NRS2 detector offset; wavelength-dependent offsets are not tested and could bias the flatness finding and the model limits.","rationale":"I read the paper's central claim as the featureless transmission spectrum and the resulting exclusions of low-MMW/low-metallicity atmospheres. The analysis is careful: two independent reductions, nested-sampling model comparison, and consistent results between chi-square and Bayesian approaches. The escape argument is suggestive but not load-bearing for the spectral interpretation. The most load-bearing assumption is the constant NRS1-NRS2 offset, because it underpins both the flatness assessment and all physical model comparisons. The paper does not provide a test for wavelength dependence of this offset. This matches the reader's weakest_assumption. I agree with the reader's conditional verdict: the paper should either test this assumption or soften the abstract's unconditional exclusions. The abstract overstatement is a secondary concern, but the offset test is the one concrete check that could change the central claims. No ad hominem; the issue is a modeling assumption, not a question of integrity.","tokens_in":19677,"tokens_out":4531,"duration_ms":50460,"concrete_test":"Re-run the non-physical flat-model fit on the 53-bin transmission spectrum adding a linear (and optionally quadratic) wavelength term per detector, i.e., a slope in transit depth versus wavelength for NRS1 and NRS2, in addition to the constant offsets. Then recompute the Bayesian evidence (flat + slope model versus Gaussian model) and re-run the physical model retrievals (metallicity and H2O-H2 grids) with the same slope terms. If the preferred model changes, or if the 3-sigma exclusion contours shift by more than the reported uncertainties, the constant-offset assumption is falsified and the central constraints require revision. A complementary check is to split each detector into two or three wavelength sub-bins and fit independent offsets per sub-bin; if the offsets differ by more than their 1-sigma uncertainties, the offset is wavelength-dependent.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central quantitative claims are the exclusions of MMW < 8 g/mol and metallicity < 300-500x solar. These constraints are derived by comparing the observed transmission spectrum to model spectra while allowing a single vertical offset per NIRSpec detector (Section 3.1, Table 3). The offset is treated as a constant and absorbed as a free parameter. However, if the detector-to-detector systematic varies with wavelength (e.g., a slope, curvature, or fringing within NRS1 or NRS2), the constant-offset model will leave wavelength-dependent residuals. Those residuals could be misinterpreted as atmospheric features, or conversely could absorb real features, biasing the flat-spectrum conclusion and the derived exclusion contours. The paper tests time-dependent systematics (exponential ramp, linear/quadratic time terms) and limb-darkening choices, but never tests a wavelength-dependent offset. The two reductions agree in offset amplitude (56 vs 57 ppm), but both reductions share the same instrument and similar systematics, so agreement does not demonstrate constancy. Without a test for wavelength dependence, the claimed 3-sigma exclusions are not fully robust. The abstract also states the exclusions unconditionally, while Section 3.2 shows low-MMW atmospheres remain possible with high-altitude clouds, but the offset assumption is the more fundamental issue because it affects all model comparisons.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"Adams Redai et al. present a single JWST/NIRSpec G395H transmission observation of the super-Earth GJ 357 b, reduced independently with the Tiberius and Eureka! pipelines. From white-light and 53-bin spectroscopic light-curve fits they obtain a spectrum that is consistent with a flat line plus a constant offset between the NRS1 and NRS2 detectors; a non-physical Gaussian-feature model is mildly disfavored by Bayesian evidence. Comparing the binned spectrum to 1D equilibrium-chemistry and H2O-H2 forward models, they report 3-sigma exclusions of mean molecular weight below about 8 g/mol and metallicity below about 300-500x solar for cloud-free cases, with a high-altitude cloud/haze caveat stated in the body. They combine mass-radius constraints and energy-limited escape calculations to argue that a primordial H2-rich envelope would have escaped, and conclude that GJ 357 b most likely has either a high-MMW secondary atmosphere (e.g., CO2/O2 rich) or no atmosphere at all. The paper also predicts that an archived JWST MIRI F1500W secondary eclipse can provide tentative discrimination between these scenarios.","tokens_in":19924,"tokens_out":15084,"duration_ms":158928,"significance":"If the reported constraints hold, this is a valuable addition to the small but growing JWST sample of warm, rocky planets around M dwarfs with featureless transmission spectra. The paper's strengths include two independent reductions with consistent results, use of publicly available reduction and modeling tools, high per-bin precision (18-27 ppm), and clear presentation of the model-dependent exclusion contours. The quantitative lower bounds on mean molecular weight and metallicity are useful for population synthesis and for planning future observations, and the MIRI eclipse prediction is concrete and testable. The result is not paradigm-breaking, but it is exactly the kind of careful atmospheric constraint that the field currently needs.","major_comments":[{"comment":"The central quantitative claims - the 3-sigma exclusions of MMW < 8 g/mol and Z < 300-500x solar - are derived after modeling the NRS1-NRS2 discontinuity with a single, wavelength-independent vertical offset per detector. The paper tests time-dependent systematics and limb-darkening choices, but it never tests a wavelength-dependent component of this offset (e.g., a slope, curvature, or fringing within NRS1 or NRS2). Because the molecular features of interest are also wavelength-dependent, such a systematic could either mimic or mask spectral features and thereby bias the flatness conclusion and the exclusion contours. Agreement between the Tiberius and Eureka! reductions does not remove this concern, since both reductions use the same instrument data and similar systematics. I recommend adding tests with per-detector linear or low-order polynomial offset terms in both the non-physical and physical model fits, and/or deriving the exclusions independently from NRS1 and NRS2 and from wavelength subsets, to demonstrate that the reported 3-sigma boundaries are robust to the offset parameterization.","section":"Sections 3.1-3.2; Table 3; Figs. 2 and 4"},{"comment":"I am unable to reproduce the quoted escape rate and lifetimes from the stated inputs. With F_XUV = 1.156e2 erg/s/cm2, R_p = 1.217 R_Earth, M_p = 1.84 M_Earth, a = 0.035 AU, and eta = 0.3, Equation (6) gives about 7e4 kg/s, not 6.63e5 kg/s; the corresponding lifetime for the 0.01 wt% H2-He envelope is about 0.5 Gyr, not 50 Myr. Similarly, the 1.97 wt% envelope under the saturation flux of about 1.13e5 erg/s/cm2 is lost in roughly 100 Myr (or about 10 Myr if the paper's 6.63e5 kg/s rate is used), not 500 kyr. The qualitative conclusion that a primordial envelope is unlikely to survive may still hold, but the numerical values and the '50 Myr' and '500 kyr' statements need to be corrected and checked. If F_XUV was intended to be 1.156e3 erg/s/cm2, that value and the conversion to L_XUV should be stated consistently.","section":"Section 4.1, Eq. (6)"},{"comment":"The abstract and the summary bullets state that MMW <= 8 g/mol and metallicity <= 300-500x solar are ruled out without the high-altitude cloud caveat that is explicit in Section 3.2 ('A low MMW atmosphere remains possible only if the atmosphere has a high altitude cloud or haze layer (e.g., < 10^-2 bar; Figure 4)'). As written, the headline claims overstate the constraints. The abstract and conclusions should carry the same condition, for example 'in the cloud-free case' or 'for opaque pressure levels above about 10^-2 bar'.","section":"Abstract and Section 5"}],"minor_comments":[{"comment":"There is a missing space in 'theTiberius pipeline', and the text refers to 'GJ-527-b' where 'GJ 357 b' is intended.","section":"Section 2.2.1"},{"comment":"The typeset manuscript title contains 'COMP ASS' and 'T ransmission'; these should be 'COMPASS' and 'Transmission'.","section":"Title and Abstract"},{"comment":"The text uses 'Baysian' instead of 'Bayesian' in the description of the model comparison approaches.","section":"Section 3.2"},{"comment":"The notation is confusing because the text reports an X-ray luminosity L_X in erg/s and then an XUV flux F_XUV in erg/s/cm2 without explicitly stating how L_XUV in watts is obtained for Equation (6); please state the conversion relation used.","section":"Section 4.1"},{"comment":"The caption states 'MMW <~ 10 g/mol' for the metallicity panels, while the text quotes a range of 10-15 g/mol for the corresponding threshold metallicities; these numbers should be harmonized.","section":"Figure 4 caption"},{"comment":"There is a typo in 'the tranmission spectrum'; it should be 'transmission spectrum'.","section":"Section 4.3"}],"recommendation":"major_revision","confidential_remarks":"This is a solid, well-executed observational paper, and I do not see grounds for rejection. The main risk is that the headline exclusion claims rest on an untested assumption of wavelength-independent detector offsets; that needs to be addressed with explicit tests. The escape section also contains numerical inconsistencies that should be corrected. I recommend a focused revision rather than a new round of broad changes."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Bottom line: this is a solid, well-executed non-detection paper, the first NIRSpec G395H transmission spectrum of GJ 357 b, and the new exclusion limits (MMW <8 g/mol, metallicity <300-500x solar) improve on the prior NIRISS/SOSS constraint. The spectrum is featureless, and the result is a clean addition to the growing COMPASS population sample.\n\nWhat the paper does well: two fully independent reductions (Tiberius and Eureka!) that agree within uncertainties, a careful non-physical feature search with Bayes factors, and a consistent model-comparison analysis using both chi2 and Bayesian retrievals. The authors are appropriately careful about the cloud degeneracy in the body text, noting that a low-MMW atmosphere remains possible if the cloud top is at high altitude (<10^-2 bar). They also ship data products on Zenodo and use open-source tools, which is reproducible and a credit to the program.\n\nWhere it gets soft: the abstract states the MMW and metallicity exclusions as unconditional, which is an overstatement; the body correctly limits them to opaque pressure levels above ~10^-4 bar. That should be fixed in the abstract no matter what else happens. The more substantive concern is the treatment of the NRS1-NRS2 offset as a single constant vertical shift per detector. The paper tests time-dependent systematics but never a wavelength-dependent offset (e.g., a slope or curvature within a detector). If such a systematic is present, it could bias the measured flatness and the derived exclusion contours. The two reductions agree in offset amplitude (56 vs 57 ppm), but both share the same instrument and similar 1/f correction, so agreement is not a test of wavelength constancy. I think this is a legitimate limitation, though not a fatal one: the spectrum is flat by eye, the Gaussian-feature test prefers the flat model, and the exclusion limits are order-of-magnitude scale. Still, the authors should either test a per-detector slope or state the limits as conditional on the offset being constant.\n\nThe escape argument is fine as a consistency check, not load-bearing. The discussion of secondary atmosphere stability is honest about the model disagreements.\n\nOverall: a worthwhile paper that deserves a serious referee. The main fixes are a corrected abstract and a robustness test for the wavelength dependence of the detector offset. I'd cite it as a data point in population work, but I wouldn't center anything on the exact limits without the extra test.","headline":"Solid single-transit non-detection that sharpens the GJ 357 b constraints, but the abstract overstates the exclusion limits and the constant detector-offset assumption deserves a second look.","tokens_in":20580,"tokens_out":3268,"would_cite":true,"duration_ms":36847,"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":"JWST's NIRSpec G395H spectrum of the warm super-Earth GJ 357 b is featureless, and forward models exclude low-mean-molecular-weight and low-metallicity atmospheres at 3σ, leaving a heavy secondary atmosphere or a bare rock.","keywords":["GJ 357 b","super-Earth","transmission spectroscopy","NIRSpec G395H","JWST","exoplanet atmospheres","mean molecular weight","atmospheric escape"],"falsifier":"Split the observed visit into halves and refit the detector offset separately for each half; if the two inferred offsets differ by more than their uncertainties, the flat-spectrum conclusion and the atmospheric exclusions would need revision.","tokens_in":19467,"feed_emoji":"🪐","tokens_out":8351,"duration_ms":80757,"temperature":0.7,"pith_summary":"This paper reports the JWST NIRSpec G395H transmission spectrum of GJ 357 b, a warm ($T_{\\mathrm{eq}}\\approx 525$ K) rocky super-Earth orbiting a nearby M dwarf at 9.44 pc. The spectrum, binned into 53 channels with median precisions of 18 and 27 ppm on the two detectors, is flat: no molecular absorption features appear, and a two-flat-line model is preferred over a model with an agnostic Gaussian feature. Comparing the data with 1D forward models rules out atmospheres with mean molecular weight below $8$ g/mol and metallicities below roughly $300$–$500\\times$ solar at $3\\sigma$, for cloud tops above about $10^{-4}$ bar. The paper concludes that GJ 357 b most likely has either a high-mean-molecular-weight secondary atmosphere, perhaps rich in CO$_2$ or O$_2$, or no atmosphere at all. This matters because it adds one of the closest super-Earths to the evidence that warm rocky planets around M dwarfs rarely retain light primordial envelopes, and it sets up a scheduled thermal-emission observation to distinguish the two remaining scenarios.","feed_headline":"JWST spectrum rules out light atmospheres on super-Earth GJ 357 b","feed_subtitle":"A 3–5 µm look at the warm rocky world shows no spectral features; only heavy CO2/O2-type air or bare rock remains.","key_machinery":"The argument is carried by the flat transmission spectrum together with a specific treatment of a known instrument systematic. The 53 spectroscopic channels are fit with two zero-slope lines, one per detector, allowing a single constant vertical offset between the NRS1 and NRS2 detectors; a Bayes factor of $0.49$–$0.68$ prefers this flat model over a model that adds a Gaussian feature. The physical exclusions come from forward models: chemical-equilibrium spectra at multiples of solar metallicity, H$_2$O–H$_2$ mixtures, an analytical pressure–temperature profile, and a transmission-spectrum code, all compared with the data using both $\\chi^2$ tests and Bayesian retrievals with an error-inflation term. The detector offset is the load-bearing systematic, since absorbing it as one fitted constant per detector is what prevents a known instrumental jump from masquerading as an atmospheric feature.","core_discovery":"The central claim is that the featureless 3–5 μm transmission spectrum of GJ 357 b is an informative null result. Against chemical-equilibrium models, the data exclude metallicities below about $300$–$500\\times$ solar, and against H$_2$O–H$_2$ mixtures they exclude mean molecular weights below about $8$ g/mol, both at $3\\sigma$, for opaque pressure levels above roughly $10^{-4}$ bar. Because the planet's bulk density allows at most a $\\sim$180 bar H$_2$–He envelope and energy-limited escape would strip such an envelope within about 50 Myr, a primordial low-MMW atmosphere is implausible at the planet's $\\gtrsim$5 Gyr age. The paper therefore argues that the two viable states are a high-MMW secondary atmosphere, most plausibly O$_2$- or CO$_2$-rich given preferential hydrogen loss, or a bare rock with no atmosphere, which fits the data at $0.3\\sigma$.","pith_inferences":["A natural extension is to apply the same two-offset-line analysis to the other planets in the same survey; if most of them also come back flat, the conclusion that M-dwarf super-Earths routinely lose their primordial envelopes becomes a population statement rather than a single-object result.","The escape-lifetime argument assumes an energy-limited efficiency of 30%; if the true efficiency is much lower, a heavier primordial envelope could survive longer, and the interpretation would shift from 'escaped long ago' to 'never accreted in appreciable amounts.'","Thermal emission at longer wavelengths than the single F1500W point would do more than separate airless from aired: a full MIRI spectrum of the 15 μm CO$_2$ band could directly measure the secondary atmosphere's composition if one is present.","Time-resolved fits of the detector offset on this same visit would directly test the weakest assumption, and could be reported as a robustness check in a follow-up paper."],"forward_implications":["A primordial hydrogen-dominated envelope is ruled out at $3\\sigma$, so GJ 357 b joins the growing set of warm rocky planets around M dwarfs with no detectable low-mean-molecular-weight atmosphere.","If an atmosphere exists, it must be a high-mean-molecular-weight secondary atmosphere, and evolutionary escape models make a CO$_2$- or O$_2$-rich composition more likely than H$_2$O- or CH$_4$-rich air.","The single archived MIRI F1500W secondary eclipse should distinguish a bare basalt surface from an atmosphere with $\\gtrsim$0.1 bar CO$_2$ at $\\gtrsim$2$\\sigma$, giving a near-term empirical test.","A joint analysis with the published NIRISS/SOSS spectrum could push the metallicity exclusion beyond $500\\times$ solar, but because both spectra are flat it will not separate a bare rock from a high-MMW atmosphere with high clouds."],"supporting_citations":[{"why":"supplies the planet mass, radius, and transit ephemeris used in all light-curve fits.","marker":"Luque et al. 2019"},{"why":"provides the X-ray luminosity and the 5 Gyr lower age limit that anchor the escape-lifetime calculation.","marker":"Modirrousta-Galian et al. 2020"},{"why":"gives the energy-limited escape framework and the expectation that hydrogen is lost while oxidized species remain.","marker":"Luger & Barnes 2015"},{"why":"models the self-consistent outcome of primordial-envelope erosion on M-dwarf rocky worlds, predicting O2- or CO2-rich secondary atmospheres.","marker":"Krissansen-Totton et al. 2024"},{"why":"reports a similarly featureless JWST transmission spectrum of a warm rocky planet, the comparison class the paper's result joins.","marker":"Moran et al. 2023"},{"why":"provides the NIRISS/SOSS transmission spectrum of the same planet whose weaker constraints this G395H spectrum improves.","marker":"Taylor et al. 2025"},{"why":"supplies the thermodynamic data used in the chemical-equilibrium forward models.","marker":"Wogan et al. 2024"},{"why":"provides the transmission-spectrum code used to generate synthetic spectra for the model comparisons.","marker":"Batalha et al. 2019"}],"fun_headline_variants":["JWST excludes light atmospheres on super-Earth GJ 357 b","Featureless JWST spectrum: GJ 357 b may be bare rock or CO2-rich","No low-MMW air: JWST data narrow GJ 357 b to heavy or none","Super-Earth GJ 357 b: JWST rules out thin hydrogen atmospheres","JWST: GJ 357 b's flat spectrum rules out metal-poor air"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The atmospheric limits assume that the brightness offset between the two detectors is a single constant that does not change with wavelength or time; if that offset drifts, the measured flatness and the resulting exclusions could be biased.","fun_headline_variants_meta":{"raw":{"variants":["JWST excludes light atmospheres on super-Earth GJ 357 b","Featureless JWST spectrum: GJ 357 b may be bare rock or CO2-rich","No low-MMW air: JWST data narrow GJ 357 b to heavy or none","Super-Earth GJ 357 b: JWST rules out thin hydrogen atmospheres","JWST: GJ 357 b's flat spectrum rules out metal-poor air"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000897,"raw_usage":{"total_tokens":3921,"prompt_tokens":1061,"completion_tokens":2860,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":677,"completion_tokens_details":{"reasoning_tokens":2752}},"tokens_in":677,"tokens_out":2860,"duration_ms":20738,"temperature":1.0,"reasoning_tokens":2752,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T18:46:59.180489+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Split the observed visit into halves and refit the detector offset separately for each half; if the two inferred offsets differ by more than their uncertainties, the flat-spectrum conclusion and the atmospheric exclusions would need revision.","supporting_citations":[{"cited_title":"2020, Astronomy and Astrophysics, 641, A113, doi: 10.1051/0004-6361/202038280","cited_arxiv_id":null,"evidence_quote":"provides the X-ray luminosity and the 5 Gyr lower age limit that anchor the escape-lifetime calculation."}],"review_version":1}