{"id":"985fc9e1-407f-4f6c-8bd8-2504ee9b9f60","arxiv_id":"2506.04605","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":7,"one_line_summary":"HIP94235b shows no detectable helium escape (mass loss below 10^11 g/s) and no detectable water absorption in two CRIRES+ transits, implying it likely lacks a large hydrogen-helium envelope.","lead":"Two transit observations of the young sub-Neptune HIP94235b found no escaping helium and no water vapor, placing an upper limit on its atmospheric mass loss. The result suggests the planet has already shed most of its primordial hydrogen-helium envelope by 120 million years of age.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 10^11 g/s mass-loss upper limit is the load-bearing result; it depends on p-winds with fixed T=6000 K and XUV scaled from EK Dra, with no propagated uncertainty in either input.","rationale":"The reader's weakest assumption is the same one I would single out: the conversion from a credible helium non-detection to a quantitative mass-loss upper limit is dominated by unpropagated p-winds inputs, especially the EK Dra-scaled XUV flux and the fixed 6000 K wind temperature. The manuscript's own introduction flags the G-star sensitivity limitation, and Section 3.2's rounding to one significant figure acknowledges model simplicity, but no calculation shows how the limit varies under plausible alternatives. That leaves the central quantitative claim, and the 3-10% initial envelope fraction derived from it, more fragile than the observational null itself. I do not see an internal inconsistency or a data-handling error; the concern is model-dependent conservatism, which is precisely what a conditional verdict should capture. The injection-recovery results for the atmosphere search are weaker and would not change my conclusion, since the solar-metallicity exclusion is already qualified by the missing mass constraint. The reader's conditional verdict is appropriate, and no verdict change is needed.","tokens_in":13554,"tokens_out":6494,"duration_ms":67046,"concrete_test":"Re-run the p-winds mapping in Section 3.2 with (1) an XUV flux bracket of ±0.5 dex around the EK Dra-scaled value, (2) an alternative XUV estimate derived from HIP94235's measured X-ray luminosity, and (3) T_upper = 5000, 6000, and 8000 K with He/H = 0.1 and 0.3. If the resulting 5 sigma Mdot upper limit stays within a factor of 2 of 10^11 g/s across all plausible inputs, the headline survives; if any plausible combination pushes it above 10^12 g/s, the abstract and conclusions should state that the mass-loss constraint is conditional on the assumed stellar XUV and wind temperature.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Section 3.2 converts the helium non-detection into a 5 sigma Mdot upper limit of 10^11 g/s through p-winds, a 1D Parker wind model, using T_upper = 6000 K, H number fraction = 0.9, and an XUV flux scaled from the 100 Myr G star EK Dra. The paper reports visit limits of 7.5e10, 3.9e10, and 3.9e10 g/s, then rounds to 10^11 'to reflect uncertainties' without propagating any specific uncertainty in the model inputs. This matters because the metastable helium triplet is not a linear tracer of mass loss: the 2^3S population is controlled by the balance between recombination and photoionization, and a G-type stellar SED can suppress the triplet population for the same outflow. The authors themselves note in the introduction that helium is most effective around K-type stars. If HIP94235's true XUV flux is lower than the EK Dra-scaled value, or its SED produces less metastable helium per unit mass loss, the same observed null would be consistent with Mdot well above 10^12 g/s. The follow-on conclusion that the initial envelope fraction is 3-10% inherits this same assumption through the energy-limited evolution models of Section 3.3. The non-detections and data reduction are credible; the quantitative headline is the fragile link.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper presents CRIRES+ Y-band transit spectroscopy of the young sub-Neptune HIP94235b over two transits. The authors search for excess metastable helium at 1083 nm and for water vapor via high-resolution cross-correlation, reporting null detections in both searches. Using the p-winds 1D Parker wind model with an assumed upper-atmosphere temperature of 6000 K, a hydrogen fraction of 0.9, and an XUV flux scaled from EK Dra, they convert the helium non-detection into a 5 sigma mass-loss rate upper limit of about 10^11 g/s. They then use energy-limited photoevaporation models to infer an initial envelope mass fraction of 3-10% of the planet mass. Injection-recovery tests show that a 10x solar metallicity 5 Earth-mass template would be retrievable at the 3 sigma level, while a solar metallicity template is recovered at only 2 sigma.","tokens_in":13743,"tokens_out":4824,"duration_ms":48298,"significance":"If the quantitative constraints hold, this is a valuable addition to the sparse sample of escape searches around young sub-Neptunes. The data reduction is careful, the median stellar subtraction and residual maps are clearly presented, and the injection-recovery tests are a useful check on the cross-correlation methodology. The paper's strongest contribution is the direct null detection and its demonstration that the observations would have been sensitive to some atmospheric models. However, the headline mass-loss upper limit and the follow-on evolutionary constraint rest on unpropagated model assumptions, particularly the stellar XUV/SED scaling, and the paper overstates the robustness of the 'likely lacks a large hydrogen-helium envelope' conclusion.","major_comments":[{"comment":"The conversion of the helium non-detection into a 5 sigma Mdot upper limit of 10^11 g/s is highly model-dependent, and no sensitivity analysis is provided. The p-winds calculation assumes T=6000 K, a hydrogen number fraction of 0.9, and an XUV flux scaled from EK Dra, but the metastable helium population is sensitive to both the magnitude and spectral shape of the ionizing flux. As the paper itself notes in Section 1, helium is most effective as an escape tracer around K-type stars; for a G-type host the same mass-loss rate can produce weaker helium absorption. A lower true XUV flux or a less favorable SED would permit mass-loss rates well above 10^11 g/s. Please provide a grid of p-winds models over plausible ranges of T, H fraction, and XUV scaling (for example 0.1-10x the EK Dra-scaled value) and report the resulting range of Mdot limits, or state the limit as explicitly conditional on the adopted XUV model. As written, the abstract and conclusions present the limit without this essential caveat.","section":"Section 3.2"},{"comment":"The inferred initial envelope mass fraction of 3-10% inherits the same XUV model dependence as the mass-loss upper limit. The text states that this constraint follows from incorporating Mdot < 10^11 g/s into the energy-limited evolution models, so it is only as strong as the p-winds conversion. If the helium null is consistent with Mdot up to 10^12 g/s under alternative XUV assumptions, the allowed initial envelope fraction could be substantially larger. The authors should show how the envelope fraction constraints vary with the alternative Mdot limits derived from the sensitivity grid requested above; without this, the conclusion that HIP94235b 'likely lacks a large hydrogen-helium envelope' is not adequately supported.","section":"Section 3.3"},{"comment":"The planet mass used in the p-winds model is not stated in this section. The mass-loss rate corresponding to a given helium absorption depends on the planet's gravitational potential, and HIP94235b has no measured mass; the paper assumes 5 Earth masses later for the transmission models, but it is unclear whether the same mass is used for the p-winds calculation. Please specify the adopted planet mass for the mass-loss modeling and show how the Mdot upper limit changes for plausible masses (for example 3 and 10 Earth masses). This is necessary for reproducibility and for assessing the robustness of the quoted limit.","section":"Section 3.2"}],"minor_comments":[{"comment":"There are several typographical errors, including 'HIP 943235 b' instead of HIP 94235 b in Section 1, 'reaonsable' in Section 3.2, 'of lines of lines' in Section 1, and 'T op' in the Figure 3 caption. A careful proofread is needed.","section":"Throughout"},{"comment":"The set of excluded orders is inconsistent: Section 3 states orders 1, 8, and 9 are discarded, while Section 4.2 states orders 1, 6, 8, and 9 are excluded. Please clarify which orders are used in the helium analysis and which in the cross-correlation analysis.","section":"Section 4.2"},{"comment":"The statement that a 10x solar metallicity atmosphere 'would have been retrievable if present' is based on a 3.0 sigma injection-recovery significance, which is marginal. Please phrase this conclusion with the significance level explicit, and consider whether 3 sigma meets the intended retrieval threshold.","section":"Section 4.4"},{"comment":"The overplotted light curves for Mdot = 10^11 and 10^12 g/s are useful, but the text does not describe how these mass-loss rates are converted into transit-depth light curves. A brief explanation in Section 3.2 would make the figure self-contained.","section":"Figure 5"}],"recommendation":"major_revision","confidential_remarks":"The observational analysis is competent and the null detections appear credible, but the paper's central quantitative claims are over-interpreted relative to the model assumptions. The requested sensitivity analysis is essential before publication; without it, the 10^11 g/s limit and the 3-10% envelope fraction should not appear as headline results. The manuscript also needs a thorough proofread."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Take this as a well-executed null result, not a detection paper. Two CRIRES+ transits of the 120 Myr sub-Neptune HIP94235b, median stellar subtraction, telluric masking, clear baselines, and injection-recovery checks: the work is diligent. The helium non-detection is credible, and the mass-loss upper limit of 10^11 g/s is a reasonable order-of-magnitude statement given the p-winds assumptions. The paper's real value is adding a G-type-host young planet to the still-small census of helium escape searches, most of which have also been nulls.\n\nWhat's new: first helium and Y-band molecular search for this target. The methods are standard, but that's fine; the object is the novel part. The water cross-correlation shows no detection, and the injection-recovery demonstrates that a 10x-solar metallicity template would have been seen at ~3 sigma. That is a useful sensitivity statement.\n\nSoft spots, in order of actual softness. The mass-loss upper limit is not a direct measurement. It depends on p-winds with T=6000 K, H:He=0.9, and XUV scaled from EK Dra. The authors round 3.9-7.5e10 up to 10^11 to reflect this, but they don't propagate any specific uncertainty. If the true XUV flux is lower or the SED less favorable to metastable helium, the same null could hide a much higher mass-loss rate. They are honest about this in the text, but the abstract states the limit without the hedge. The 3-10% initial envelope fraction from the energy-limited evolution models inherits the same XUV assumption; treat it as a model-dependent illustration, not an empirical constraint. The water conclusion is the weakest point: the solar-metallicity template recovers at only 2.1 sigma, yet the paper says 'solar metallicity atmosphere is unlikely.' That's overstated even with the 'if low density' qualifier. A 2 sigma injection-recovery limit doesn't exclude anything.\n\nNone of this undermines the core non-detections. The paper doesn't claim a detection; it reports nulls and interprets them with appropriate caveats. The citation pattern is normal, and the discussion of prior young-planet targets (V1298 Tau, TOI-1807, K2-100) is accurate.\n\nWho should read it: anyone working on atmospheric escape or the evolution of small planets. It's a solid data point, not a paradigm shift. A serious referee should engage because the target is valuable and the analysis is careful, even though the headline number shrinks to 'unconstrained at the factor-of-a-few level' when you propagate the model assumptions.\n\nRecommendation: send to peer review. I'd accept it with minor revision suggestions—mainly softening the 'unlikely' language and making the XUV/model-dependence more prominent in the abstract.","headline":"Solid null results for a valuable young sub-Neptune; the helium and water non-detections are credible, while the mass-loss and envelope constraints are model-dependent and should be read with the paper's own caveats in mind.","tokens_in":14433,"tokens_out":3727,"would_cite":true,"duration_ms":33692,"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":"This paper argues that the 120-million-year-old sub-Neptune HIP94235b shows no detectable helium escape, with a present-day mass-loss upper limit of $10^{11}$ g/s and an initial hydrogen-helium envelope of only 3--10 percent of its mass.","keywords":["exoplanet atmospheres","atmospheric escape","metastable helium","sub-Neptune","photoevaporation","transmission spectroscopy","high-resolution spectroscopy","young planets"],"falsifier":"A future transit observed at higher signal-to-noise that detects the 1083 nm helium triplet in absorption at the planet's expected velocity, together with a stellar XUV measurement showing HIP94235's high-energy flux is at least as strong as assumed, would overturn the $10^{11}$ g/s upper limit. A JWST transmission spectrum revealing prominent water or methane features from a low-metallicity hydrogen-helium atmosphere would contradict the conclusion that HIP94235b lacks a large envelope.","tokens_in":13216,"feed_emoji":"🪐","tokens_out":8431,"duration_ms":75161,"temperature":0.7,"pith_summary":"Using two transits observed with the infrared spectrograph CRIRES+, this paper searches for signs of ongoing atmospheric escape from the 120-million-year-old sub-Neptune HIP94235b. It finds no excess absorption in the metastable helium triplet at 1083 nm and no trace of water in the Y-band transmission spectrum. Converted through a one-dimensional Parker wind model, the helium non-detection sets an upper limit on the planet's current mass loss rate of $10^{11}$ g/s. Energy-limited evolution models then restrict the planet's initial hydrogen-helium envelope to 3--10 percent of its total mass. If correct, the planet was stripped of its primordial gas very early, matching the picture in which photoevaporation reshapes close-in small planets.","feed_headline":"No helium escape from a 120-million-year-old sub-Neptune","feed_subtitle":"Two infrared transits cap its mass loss below 10^11 g/s, hinting at a stripped rocky world.","key_machinery":"The load-bearing tool is the metastable helium triplet at 1083.33 nm, a spectral feature that traces neutral helium escaping from a planet's upper atmosphere and is immune to the interstellar absorption that cripples Lyman-$\\alpha$ observations. The analysis pipeline removes stellar and telluric features by fitting telluric models and dividing out a median stellar spectrum, then integrates the residual flux in a 0.15 nm window to build a helium light curve. To turn the measured sensitivity into a physical limit, the authors fit a light-curve model to set the shallowest detectable transit depth and feed that through a one-dimensional Parker wind model of the escaping atmosphere, assuming a 6000 K upper atmosphere, a hydrogen fraction of 0.9, and XUV irradiation scaled from the young Sun-like star EK Dra. For the molecular search, synthetic transmission spectra from line-by-line radiative transfer are cross-correlated with the residuals, and injection-and-recovery tests quantify which model atmospheres would have been detectable.","core_discovery":"The central discovery is a null result with a quantitative consequence: across two independent CRIRES+ transits, HIP94235b shows no detectable metastable helium absorption, no variability in the helium light curve, and no water signal in cross-correlation with synthetic transmission spectra. The authors convert the helium light-curve noise into a $5\\sigma$ upper limit on extra transit depth of about 0.0015, which the Parker wind model translates into a mass-loss upper limit of $10^{11}$ g/s ($0.53\\,M_\\oplus$/Gyr). Combining that limit with energy-limited photoevaporation tracks implies the planet's initial envelope mass fraction was only 3--10 percent. They therefore conclude that HIP94235b likely lacks a large hydrogen-helium envelope today, consistent with its earlier Lyman-$\\alpha$ non-detection and with models in which most small planets lose their primordial envelopes within 100 Myr.","pith_inferences":["Because helium is a less sensitive escape tracer around G-type stars than around K-type stars, the non-detection may underestimate the true escape rate; a direct measurement of HIP94235's XUV luminosity would test the assumed irradiation level.","If the energy-limited mass-loss efficiency is lower than assumed, the same present-day mass-loss cap would allow a larger initial envelope; independent constraints on the planet's core mass would break this degeneracy.","A similar helium survey of young sub-Neptunes around K-type hosts would be a sharper test of whether photoevaporation strips envelopes within 100 Myr, since the metastable helium signal is strongest there.","The apparent absence of a large H/He envelope leaves open a water-rich or steam-atmosphere composition; a JWST transmission spectrum at longer wavelengths could distinguish that scenario from a bare rocky core."],"forward_implications":["The present-day mass-loss rate of HIP94235b is below $10^{11}$ g/s, so the planet is not shedding its atmosphere at an observable rate at 120 Myr.","The planet's initial envelope must have been only 3--10 percent of its mass, ruling out a formation history as a gas-rich 40-percent-envelope Neptune like those seen around V1298 Tau or HIP67522b.","The helium null reinforces the earlier Lyman-$\\alpha$ null, making it unlikely that HIP94235b retains any substantial hydrogen-helium envelope today.","Ground-based infrared high-resolution spectroscopy is nearly sensitive enough to detect water in a low-metallicity sub-Neptune: a 5 $M_\\oplus$, 10$\\times$ solar-metallicity cloud-free model would have been recovered at the $3\\sigma$ level.","The absence of active escape and of molecular features is consistent with either a stripped rocky core or a heavy, volatile-rich envelope, both endpoints expected from photoevaporation models."],"supporting_citations":[{"why":"established metastable helium absorption during transit as a practical tracer of atmospheric escape.","marker":"Spake et al. 2018"},{"why":"provided the theoretical model linking metastable helium triplet absorption to the escape rate and stellar ionizing flux.","marker":"Oklopčić & Hirata 2018"},{"why":"supplied the EK Dra XUV spectrum used to scale the assumed high-energy irradiation of HIP94235.","marker":"Ribas et al. 2005"},{"why":"provided the one-dimensional Parker wind model used to convert the helium transit-depth upper limit into a mass-loss rate limit.","marker":"Dos Santos et al. 2022"},{"why":"discovered HIP94235b and supplied the stellar parameters, age, and transit ephemeris used throughout.","marker":"Zhou et al. 2022"},{"why":"reported the earlier Lyman-α non-detection for the same planet, which the helium limit extends.","marker":"Morrissey et al. 2024"},{"why":"contributed the energy-limited photoevaporation tracks used to constrain the initial envelope mass fraction.","marker":"Owen & Wu 2017"},{"why":"provided the radiative-transfer framework for the synthetic transmission templates used in the water cross-correlation search.","marker":"Mollière et al. 2019"}],"fun_headline_variants":["No helium escape from young sub-Neptune, likely stripped to rock","Two CRIRES+ transits cap mass loss below 10^11 g/s for HIP94235b","Young sub-Neptune shows no helium or water, suggests bare core","Photoevaporation stripped HIP94235b's atmosphere within 100 Myr"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The mass-loss cap rests on assuming that HIP94235 irradiates its planet as strongly as the young Sun-like star EK Dra, with a 6000 K upper atmosphere and a 0.9 hydrogen fraction; if the star's XUV output is lower, the same helium non-detection would allow faster escape.","fun_headline_variants_meta":{"raw":{"variants":["No helium escape from young sub-Neptune, likely stripped to rock","Two CRIRES+ transits cap mass loss below 10^11 g/s for HIP94235b","Young sub-Neptune shows no helium or water, suggests bare core","Photoevaporation stripped HIP94235b's atmosphere within 100 Myr"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000316,"raw_usage":{"total_tokens":1819,"prompt_tokens":1007,"completion_tokens":812,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":623,"completion_tokens_details":{"reasoning_tokens":723}},"tokens_in":623,"tokens_out":812,"duration_ms":7216,"temperature":1.0,"reasoning_tokens":723,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T10:46:34.310534+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A future transit observed at higher signal-to-noise that detects the 1083 nm helium triplet in absorption at the planet's expected velocity, together with a stellar XUV measurement showing HIP94235's high-energy flux is at least as strong as assumed, would overturn the $10^{11}$ g/s upper limit. A JWST transmission spectrum revealing prominent water or methane features from a low-metallicity hydrogen-helium atmosphere would contradict the conclusion that HIP94235b lacks a large envelope.","supporting_citations":[{"cited_title":"P., Huang, C","cited_arxiv_id":null,"evidence_quote":"discovered HIP94235b and supplied the stellar parameters, age, and transit ephemeris used throughout."},{"cited_title":"X., et al","cited_arxiv_id":null,"evidence_quote":"reported the earlier Lyman-α non-detection for the same planet, which the helium limit extends."}],"review_version":1}