{"id":"2a737218-5590-42b9-b92e-b92ed46c7f83","arxiv_id":"2501.11660","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Using age and metallicity, the authors infer that exoplanet host stars formed at smaller Galactic radii than non-host stars, with high-mass planet hosts forming innermost and later in time.","lead":"Exoplanet-hosting stars in the solar neighborhood appear to have been born closer to the Galactic center than stars without detected planets, with high-mass planets tracing the innermost birthplaces. The study projects stars back to their birth radii using age and metallicity, linking where planets form to the Milky Way's chemical enrichment history.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The central radial and temporal trends in F_p are not measured independently: r_birth is inferred from [Fe/H] via the assumed Minchev et al.","rationale":"I agree with the reader's verdict of CONDITIONAL. The single most load-bearing assumption is the birth-radius inversion, because the central abstract claim is built on it. If the assumed [Fe/H]-radius relation were wrong, all r_birth values shift and the radial and temporal trends in F_p would change systematically. Even if the relation is correct, the projection does not add empirical information beyond the host-single [Fe/H] and age differences; the radial dependence is a re-expression of the planet-metallicity correlation. This does not make the paper wrong, but it means the main novelty is not the spatial measurement itself. The authors explicitly concede in Sect. 4.4 that F_p is not a true frequency due to missing completeness corrections, which further weakens quantitative claims. The internal inconsistency in Sect. 4.3 (ELMPHs mean r_birth is largest, not smallest, in the quoted numbers) supports the need for a careful reframing. No ad hominem intended; the work is careful in many respects (use of homogeneous stellar parameters, two samples, KS tests, bootstrap uncertainties). The concrete test above would settle whether the observed radial trends can be reproduced solely from the metallicity correlation. If so, the verdict remains CONDITIONAL with emphasis on reframing; if not, the claims gain independent support. Since the reader already identified the same weakest assumption, I mark agreement as 'agree' and recommend no change to the verdict.","tokens_in":14807,"tokens_out":5881,"duration_ms":64297,"concrete_test":"Test whether the radial trend in F_p is independent of the [Fe/H]–planet correlation by constructing a null model: use the observed F_p vs. [Fe/H] relation (Fig. 6) as the only input, assign pseudo-r_birth to every star by applying the same Minchev et al. (2018) mapping to the star's [Fe/H] and age, and generate predicted F_p vs. r_birth and F_p vs. age curves (Figs. 8 and 9). If the null model matches the observed curves within the quoted binomial uncertainties, the central claim reduces to a remapping of the well-known planet-metallicity correlation and should be reframed accordingly. If the null model fails to reproduce the trends (e.g., an excess at low r_birth or a different mass dependence), then the radial and temporal results contain real spatial information beyond the [Fe/H] relation.","verdict_should_be":"UNCHANGED","load_bearing_attack":"In Section 3 the authors adopt the Minchev et al. (2018) method to infer r_birth from [Fe/H] and age. In this model the ISM metallicity is a strictly monotonic function of radius at each age, so the inversion assigns smaller r_birth to higher-[Fe/H] stars. Since planet hosts are systematically metal-richer (Sect. 4.1), the F_p vs. r_birth decline in Fig. 8 is, to first order, a remapping of the F_p vs. [Fe/H] increase in Fig. 6; no spatial information is added by the projection. The central abstract claim that 'formation efficiency ... decreases with galactocentric distance' is therefore not an independent measurement of a Galactic spatial trend but is imposed by the assumed chemical evolution model. The same logic applies to the time evolution in Sect. 4.5: younger stars are assigned larger r_birth because the adopted ISM gradient flattens with time, so the conclusion that high-mass planet formation 'encompasses a larger galactocentric distance over time' may be a direct consequence of the assumed flattening. The authors do not validate the Minchev et al. calibration on their own stars, and no alternative radial mapping is tested. An internal inconsistency in Sect. 4.3 (text states ELMPHs have the smallest r_birth while the quoted means show they have the largest) further suggests the radial results are not robustly interpreted. Because the qualitative picture and comparisons with models (Baba et al. 2023; Boettner et al. 2024) are consistent with the projection, the paper's value is as a conditional application, not as a new empirical constraint on the radial dependence.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper infers the Galactic birth radii of exoplanet host stars by combining stellar ages from PARAM/PARSEC isochrones with the Minchev et al. (2018) method, which maps a star's [Fe/H] and age onto the radius where the ISM had the same [Fe/H] at the star's birth. Using SWEET-Cat planet hosts (548 stars) and HARPS-GTO stars with (83) and without (491) planets, the authors find that hosts are more metal-rich, younger, and have smaller inferred r_birth than non-hosts, with high-mass planet hosts showing the strongest offsets. Defining F_p as the relative frequency of planetary systems, they report that F_p increases with [Fe/H], decreases with age, and decreases with r_birth, more steeply for high-mass than for low-mass planets; splitting by age, they report that high-mass planet formation efficiency increases with time and extends to larger galactocentric radii, in agreement with the assumed ISM enrichment and gradient flattening. They conclude that exoplanet formation follows Galactic chemical evolution.","tokens_in":14986,"tokens_out":19857,"duration_ms":186652,"significance":"If the central result were an independent measurement, the paper would establish an empirical radial and temporal map of exoplanet formation efficiency across the Galactic disk, a valuable benchmark for chemical evolution and planet formation models (Baba et al. 2023; Boettner et al. 2024). The paper has real strengths: homogeneous host and comparison samples from SWEET-Cat and HARPS-GTO, a transparent age-inference pipeline (PARAM with PARSEC isochrones), bootstrap-based uncertainties on ages and r_birth, binomial confidence intervals on F_p, KS significance tests, an explicit statement of the incompleteness caveat (Sect. 4.4), and predictions that future surveys such as PLATO can falsify. The confirmation of the planet-metallicity and planet-mass-metallicity trends is solid and useful. However, the central spatial claim is not an independent measurement: it is the well-established planet-metallicity correlation remapped through the assumed Minchev et al. (2018) ISM metallicity evolution, whose time-dependent gradient also prescribes the reported temporal expansion. Reframed as a model-conditional projection, the paper is a reasonable application with modest novelty.","major_comments":[{"comment":"The central claim of the abstract—that planet formation efficiency decreases with galactocentric distance, and that high-mass planet formation 'increases with time and encompasses a larger galactocentric distance over time'—is largely prescribed by the construction rather than measured. In Section 3, r_birth is inferred by inverting the Minchev et al. (2018) relation between [Fe/H], age, and the ISM metallicity, in which the ISM [Fe/H] is a strictly monotonic decreasing function of radius at every age; any star with above-average [Fe/H] is therefore assigned a below-average r_birth by construction. Since Fig. 6 shows that F_p increases with [Fe/H] (an independent, well-established result), the decline of F_p with r_birth in Fig. 8 is, to first order, the same relation relabeled through the assumed chemical evolution model, and the KS tests on r_birth in Table 1 are tests on a deterministic transform of [Fe/H] and age rather than on independent spatial information. The time-evolution claims (Fig. 9, Sect. 4.5) inherit the same structure: the adopted gradient flattens with time (from about -0.15 to -0.07 dex kpc^-1), so younger stars are assigned larger r_birth automatically, making the 'encompasses a larger galactocentric distance over time' conclusion a consequence of the assumed gradient flattening. Accordingly, the characterization of the method as 'semi-empirical and model-independent' (Section 3) is not supportable, and the closing statement of Section 5 that the results 'are in agreement with the observed negative ISM metallicity gradient and its enrichment and flattening with time' is circular, since that gradient is an input to the analysis. To make the central claim supportable, the authors should (i) validate the inferred r_birth against an independent estimate such as kinematic guiding radii from Gaia astrometry for the HARPS-GTO sample; (ii) test the sensitivity of Figs. 8-9 to the assumed gradient and its time evolution, e.g., by freezing the present-day gradient or by perturbing the Minchev et al. (2018) fits within their uncertainties; and (iii) examine F_p versus r_birth within fixed [Fe/H] bins, which would isolate the age-dependent part of the projection. Without such tests, the abstract's 'we show' should be revised to a model-conditional statement.","section":"§3, §4.4, §4.5, Figs. 8-9"},{"comment":"The construction of F_p in Eq. (2) is ambiguous for the SWEET-Cat panels. SWEET-Cat contains 548 host stars and no stars without detected planets, so the denominator 'total number of stars' must draw on the HARPS-GTO single-star sample; the figures (Figs. 6-8) indeed show single-star counts in the SWEET-Cat panels, but the text never states that HARPS-GTO stars are used as the denominator there. This matters because the two catalogues have different selection functions: HARPS-GTO is a volume-limited radial-velocity survey within 500 pc, whereas SWEET-Cat is a compiled catalogue of planet hosts within 2 kpc assembled from heterogeneous surveys. The paper acknowledges that 'this is not the mathematically correct way to compute the frequency of planetary systems' but then asserts that 'the observed trends should reflect the true dependencies' without demonstrating that the trends survive the incompleteness; mixing a local single-star denominator with a more distant host numerator can imprint spurious trends in age and metallicity through distance-dependent detectability. Please specify exactly how N_total is computed for each panel of Figs. 6-8, and show whether the reported trends persist when the analysis is restricted to the volume-limited HARPS-GTO sample alone or when basic completeness corrections are applied.","section":"§4.4, Eq. (2), Figs. 6-8"},{"comment":"There is a direct internal contradiction in Section 4.3. The text states that 'HMPHs have, on average, smaller r_birth than LMPHs and ELMPHs, the latter having the smallest r_birth among the three groups,' but the quoted mean values are 5.7 ± 0.1, 5.9 ± 0.2, and 6.1 ± 0.2 kpc for SWEET-Cat HMPHs, LMPHs, and ELMPHs, respectively, and 5.6 ± 0.2, 5.6 ± 0.3, and 6.0 ± 0.4 kpc for the HARPS-GTO sample. In both samples the ELMPHs have the largest mean r_birth, not the smallest; the sentence should read 'the latter having the largest r_birth.' More importantly, because Table 1 shows no statistically significant differences in r_birth among the three planet-host groups in either sample, the discussion in Section 5 should not present differences in mean r_birth between the planetary groups as a measured result.","section":"§4.3"}],"minor_comments":[{"comment":"Because systems containing both a high- and a low-mass planet are counted in both the HMPH and LMPH groups (as noted in Section 4), the KS tests comparing HMPHs with LMPHs are not comparisons of independent samples, and the two F_p curves in Figs. 6-9 are not mutually exclusive; this should be acknowledged where the tests are interpreted.","section":"§4, Table 1"},{"comment":"F_p is repeatedly called the 'formation efficiency of planets,' but Eq. (2) defines it as the ratio of detected planetary systems to sample stars with no completeness correction; a more neutral term such as 'detected planet-host fraction' would better match the quantity actually measured.","section":"Abstract; §4.4-4.5"},{"comment":"The rule that a star is retained when only one of its two age estimates (tau_G or tau_KS) falls below the 13.3 Gyr limit, with the below-limit estimate used in isolation, is asymmetric and could bias the inferred ages of the oldest stars; the authors should either justify the rule or demonstrate that it does not affect the age and r_birth distributions.","section":"§3"},{"comment":"The paper quotes mean ages and standard errors but never the typical 68% uncertainty on individual PARAM ages; because r_birth depends on age through the time-evolving metallicity gradient, the median individual age uncertainty should be reported (the acknowledgement in the discussion that ages are a key limiting factor is welcome but does not replace this information).","section":"§3, §4.2"},{"comment":"The low-mass-planet time-evolution claims rest on 23, 40, and 17 SWEET-Cat LMPHs in the three age bins (and only 19 HARPS-GTO LMPHs in total); the text should quote these counts next to the claims in abstract items (ii) and (iii) and should hedge wherever the binomial uncertainties are comparable to the reported trends.","section":"§4.5, Fig. 9"},{"comment":"The manuscript does not provide a machine-readable table of the derived ages and birth radii or a data/code availability statement; providing these would materially help reproducibility.","section":"§5 (Data availability)"}],"recommendation":"major_revision","confidential_remarks":"The manuscript header shows 'Received 31 July 2024; Revised 19 December 2024; Accepted 23 December 2024; DOI: 10.1002/asna.20240076,' indicating prior acceptance at Astronomische Nachrichten; the editor should clarify the submission status and any duplication issue. Substantively, the decisive issue is the model-dependence of the birth-radius projection. I recommend that acceptance be conditional on a robustness test against an alternative ISM metallicity gradient or a kinematic validation for the HARPS-GTO subsample, and on revising the abstract's 'we show' claims to model-conditional statements."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The short version: this is a clean, careful application of Minchev et al.'s birth-radius reconstruction to two well-known planet-host samples, and the qualitative results (hosts metal-richer, younger, smaller inferred birth radii; high-mass hosts more extreme) align with earlier work. But the headline claim—that planet formation efficiency declines with galactocentric radius—is not an independent spatial measurement. Because r_birth is computed by inverting an assumed monotonic [Fe/H]-radius relation, the radial trend in F_p is largely the well-established planet-metallicity correlation remapped onto radius. The paper overstates what the projection adds.\n\nWhat earns credit: the authors are transparent. They state plainly in Section 4.4 that their F_p is not a true frequency because completeness corrections are missing. They use homogenized stellar parameters from SWEET-Cat and HARPS-GTO, derive ages with PARAM, and quote bootstrap uncertainties. The comparison with Baba et al. and Boettner et al. is sensible. The mass grouping into HMPHs/LMPHs/ELMPHs follows an observed mass gap. This is a reasonable exploratory analysis that quantifies a known expectation.\n\nThe soft spots are real and load-bearing. First, the circularity: Section 3 adopts Minchev et al.'s calibration without validating it on these stars. Since planet hosts are metal-rich, they automatically get small r_birth. The time trend in Section 4.5 is similarly driven by the assumed flattening of the gradient with time. An alternative radial mapping or a test against the data would be needed to claim a new Galactic constraint. Second, the text in Section 4.3 says ELMPHs have the smallest r_birth, while the quoted means in the same paragraph show ELMPHs with the largest (6.1 kpc vs 5.7 and 5.9 in SWEET-Cat; 6.0 vs 5.6 and 5.6 in HARPS-GTO). That is an internal inconsistency. Third, sample sizes for LMPHs and ELMPHs are small, especially in HARPS-GTO; the KS tests mostly have no power there. These issues don't erase the qualitative picture, but they do mean the central quantitative claim about F_p(r_birth) is not new empirical evidence.\n\nWho is this for? Readers interested in Galactic chemical evolution and planet demographics might use it as a worked example of the Minchev technique. It deserves a serious referee, but the authors should be asked to reframe the claims as conditional on the adopted chemical evolution model, fix the Section 4.3 contradiction, and discuss how much of the radial trend is inherited from the [Fe/H] input. I would not cite the radial-efficiency numbers in my own work.","headline":"A careful but model-dependent application of Minchev et al.'s birth-radius reconstruction; the radial gradient in F_p is essentially the planet-metallicity correlation remapped onto radius, so the central claim needs reframing.","tokens_in":15692,"tokens_out":2301,"would_cite":false,"duration_ms":23213,"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":"The formation efficiency of exoplanets decreases with galactocentric distance, and this decline is steeper for high-mass planets than for low-mass planets, tracking the Milky Way's chemical evolution.","keywords":["exoplanet formation","Galactic chemical evolution","birth radii","metallicity gradient","planet formation efficiency","stellar ages","Milky Way disk","high-mass planets"],"falsifier":"Compare the birth radii inferred from [Fe/H] and age with kinematic birth radii (guiding radii) from Gaia astrometry for the same stars; if the two do not agree, or if stars in open clusters with known distances do not lie on the assumed [Fe/H]–radius relation at their cluster age, the radial and temporal trends in formation efficiency would be artifacts of the chemical evolution model rather than real spatial patterns.","tokens_in":14443,"feed_emoji":"🪐","tokens_out":10025,"duration_ms":83129,"temperature":0.7,"pith_summary":"This paper tries to establish where in the Milky Way exoplanets preferentially form by reconstructing the Galactic birth radii of planet-hosting stars from their ages and iron abundances. The authors find that stars with planets are born closer to the Galactic center than stars without detected planets, and that this displacement is larger for stars hosting high-mass planets than for those hosting low-mass planets. They define the formation efficiency of planets as the relative frequency of planetary systems among all stars in a bin and show that this efficiency declines with galactocentric distance while rising over cosmic time for high-mass planets. The trends match the Galaxy's inside-out chemical enrichment, in which the inner disk is metal-rich and the ISM metallicity gradient flattens with time. If correct, the work connects exoplanet demographics to Galactic chemical evolution and predicts where future surveys should find the most planetary systems.","feed_headline":"Exoplanets form most efficiently in the inner Milky Way","feed_subtitle":"Planet-hosting stars are born closer to the Galactic center, with the steepest decline for high-mass planets.","key_machinery":"The central machinery is the birth-radius inference of Minchev et al. (2018), which maps a star's [Fe/H] and age to a unique Galactic birth radius by inverting logarithmic functions for the time evolution of the ISM metallicity at the solar radius and of the radial metallicity gradient. Stellar ages come from PARAM isochrone fitting with PARSEC models, using effective temperature, [Fe/H], and bolometric luminosities from Gaia and 2MASS photometry. The relative frequency $F_p = \\frac{\\text{number of planetary systems}}{\\text{total number of stars}}$ is then computed in bins of [Fe/H], age, and $r_{\\mathrm{birth}}$ as a proxy for formation efficiency.","core_discovery":"The central claim is that the formation efficiency of planets, measured as the relative frequency of stars hosting a given planet type, declines with galactocentric distance and that this decline is more pronounced for high-mass planets (≥50 Earth masses) than for low-mass planets (≤30 Earth masses). High-mass planet formation efficiency also rises with time and spreads to larger galactocentric radii, while low-mass planet efficiency is nearly flat, with a mild increase between 4 and 8 Gyr. Stars without detected planets appear to form at progressively larger galactocentric distances with time. The authors attribute these trends to Galactic chemical evolution: the ISM's negative metallicity gradient makes the inner disk metal-rich and planet-friendly, and enrichment with time allows planet formation to reach larger radii.","pith_inferences":["A direct testable extension is to compare the [Fe/H]-based birth radii with kinematic guiding radii from Gaia astrometry for the same stars; if they do not reproduce the same radial gradient, the reported $F_p$ trends would be artifacts of the chemical evolution model rather than real spatial variation.","The paper's interpretation implies that the first generation of planets formed almost exclusively in the inner disk; bulge or thick-disk planetary systems may represent an older, metal-poor population with distinct mass demographics.","The reported increase of $F_p$ with time for high-mass planets could be sharpened into a quantitative prediction for the PLATO mission: the fraction of stars hosting giant planets among young (<4 Gyr) inner-disk stars should exceed that of older populations by a measurable factor.","Because the HARPS-GTO comparison sample is small and volume-limited, a larger homogeneous survey could test whether the host-star versus single-star differences persist after accounting for detection biases."],"forward_implications":["Planet formation efficiency is highest in the inner Galactic disk and declines outward, implying that the Galaxy's planetary systems are centrally concentrated.","High-mass planets form preferentially in metal-rich, inner regions and increasingly at later times, consistent with core accretion's metallicity dependence.","Low-mass planets form more uniformly, with a slight peak at intermediate ages, suggesting their formation is less sensitive to metallicity.","The time-spreading of formation efficiency to larger radii means younger planetary systems are found farther out, a signature that can be tested with large-area surveys.","If the birth-radius mapping is correct, exoplanet occurrence rates should correlate with stellar birth radius, not just present-day Galactocentric distance."],"supporting_citations":[{"why":"Supplies the [Fe/H]-age to birth-radius mapping and the logarithmic ISM metallicity evolution functions that generate all r_birth values.","marker":"Minchev et al. (2018)"},{"why":"Defines the SWEET-Cat catalogue of planet-host stars with homogeneous stellar parameters.","marker":"Santos et al. (2013)"},{"why":"Provides the update and quality flags for the SWEET-Cat sample used here.","marker":"Sousa et al. (2021)"},{"why":"Defines the HARPS-GTO sample of stars with and without detected planets used as the comparison set.","marker":"Adibekyan et al. (2012)"},{"why":"Supplies homogeneous stellar parameters for the HARPS-GTO stars.","marker":"Delgado Mena et al. (2017)"},{"why":"Provides the PARAM code used for stellar age estimation.","marker":"Rodrigues et al. (2014)"},{"why":"Updates the PARAM code and isochrone fitting used for stellar age estimation.","marker":"Rodrigues et al. (2017)"},{"why":"Provides the PARSEC isochrone set used in age estimation.","marker":"Bressan et al. (2012)"},{"why":"Supplies astrometric distances and photometry for luminosity and sample selection.","marker":"Gaia Collaboration (2022)"}],"fun_headline_variants":["Exoplanets form most often in the inner Milky Way","Inner galaxy is the sweet spot for exoplanet formation","High-mass exoplanets favor the Milky Way's inner disk","Exoplanet birth rates drop with distance from galactic center","Milky Way's chemical evolution shapes exoplanet locations"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The entire birth-radius reconstruction rests on the adopted Minchev et al. (2018) relation between a star's [Fe/H] and age and its birth radius; if that chemical evolution calibration is wrong, every inferred $r_{\\mathrm{birth}}$ value and every trend in formation efficiency shifts systematically.","fun_headline_variants_meta":{"raw":{"variants":["Exoplanets form most often in the inner Milky Way","Inner galaxy is the sweet spot for exoplanet formation","High-mass exoplanets favor the Milky Way's inner disk","Exoplanet birth rates drop with distance from galactic center","Milky Way's chemical evolution shapes exoplanet locations"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001018,"raw_usage":{"total_tokens":4340,"prompt_tokens":1032,"completion_tokens":3308,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":648,"completion_tokens_details":{"reasoning_tokens":3226}},"tokens_in":648,"tokens_out":3308,"duration_ms":25881,"temperature":1.0,"reasoning_tokens":3226,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T17:59:56.275822+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Compare the birth radii inferred from [Fe/H] and age with kinematic birth radii (guiding radii) from Gaia astrometry for the same stars; if the two do not agree, or if stars in open clusters with known distances do not lie on the assumed [Fe/H]–radius relation at their cluster age, the radial and temporal trends in formation efficiency would be artifacts of the chemical evolution model rather than real spatial patterns.","supporting_citations":[],"review_version":1}