{"id":"f0fb5fa6-0480-449a-912c-591c79559fed","arxiv_id":"2501.10571","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"Earth-sized and Earth-irradiated planets around M/K dwarfs are mostly on near-circular orbits, with a mean eccentricity consistent with zero and one clear eccentric outlier.","lead":"Using the duration of planet transits, the authors measure the orbital eccentricities of 17 Earth-like planets around cool stars and find that most orbit almost circularly, like Earth. This matters because stable, nearly circular orbits support habitable climates and favor a calm disk-migration formation history, guiding which worlds to study for habitability.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Grazing-transit cut may preferentially exclude eccentric planets, biasing the sample toward circular orbits; injection-recovery bypasses the selection pipeline.","rationale":"The reader's weakest assumption was about unbiased stellar densities. While that is a valid concern, the paper's gamma=1 centering for the real data plus the internal validation against Gaidos for a subset provides some (though incomplete) support for the densities. A more fundamental threat is the selection pipeline: the grazing cut discards 21 of 74 candidates based on impact parameters derived from circular-orbit fits. Because eccentric transits near periastron shorten the duration and bias the fitted impact parameter upward, this cut can preferentially remove the very planets with gamma>1, flattening the eccentricity distribution. The paper's KS test on periods does not address eccentricity, and its injection-recovery exercises start from the already-selected 17 systems, so they cannot detect selection bias. This is a concrete, testable gap in the argument. However, the bias is not yet demonstrated; a simulation of the full selection would settle it. Thus the appropriate verdict remains CONDITIONAL, as the reader concluded, but for a different reason. The paper should be required to run such a selection-bias simulation before the central claim is accepted.","tokens_in":33746,"tokens_out":11844,"duration_ms":123552,"concrete_test":"Simulate the full selection pipeline: generate roughly 74 synthetic transiting planet candidates around M dwarfs with periods, radii, and impact parameters matching the original candidate distribution, but with eccentricities drawn from a known distribution (e.g., Rayleigh with mean 0.3). Inject these into Kepler/TESS light curves with realistic noise, then run the same detrending, transit fitting, and the grazing/Earth-proxy/TTV cuts as the paper. Apply the HBM to the surviving sample and compare the recovered mean eccentricity to the injected value. If the recovered mean is biased downwards by more than about 0.05, the grazing cut is confirmed to bias the sample toward circular orbits.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The most load-bearing assumption is not the unbiasedness of the stellar densities, but the impartiality of the sample selection. The grazing-transit cut removes any target for which >50% of the circular-orbit fit posterior has b > 1-p (Methods, 'Light curve fits'). For an eccentric orbit, the transit duration is modified—shorter near periastron, longer near apoastron—and the circular model tends to absorb this into a larger fitted impact parameter. Thus, eccentric planets that transit near periastron (gamma > 1) are preferentially classified as grazing and removed, truncating the high-gamma tail. The paper's KS test compares only orbital periods between grazing and non-grazing sets (p=0.96), which is insensitive to eccentricity. The injection-recovery tests (Supplementary Figure 11) inject eccentricity into the already-selected 17 targets, bypassing the selection pipeline, so they cannot detect this bias. If the grazing cut removes a non-negligible fraction of eccentric systems (21 of 74 candidates were removed as grazing), the remaining sample would be biased toward circular orbits, and the conclusion that the population is dynamically cool would be an artifact of the cut.","agreement_with_reader":"disagree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper assembles a sample of 17 transiting 'Earth proxy' planets (radius within a factor of two of Earth, instellation within a factor of four) around late-type stars and uses asterodensity profiling / the photoeccentric effect together with hierarchical Bayesian modeling to infer the ensemble eccentricity distribution. The authors report that, after excluding the outlier KOI-4087.01 (Kepler-440 b), the favored exponential model gives a mean eccentricity of 0.060 (+0.040/-0.028), and that an injection-recovery experiment with forced-circular planets produces the same inferred mean (0.061), leading them to conclude that the bulk population is dynamically cool, with KOI-4087.01 as a possible member of a rare, dynamically warmer subpopulation.","tokens_in":33977,"tokens_out":6639,"duration_ms":73360,"significance":"If the central claim holds, this is the first eccentricity distribution measurement for Earth-sized, Earth-insolated planets around M/K dwarfs, and it has direct implications for climate stability, habitability, and formation pathways. The paper has notable strengths: the posteriors and code are made available, the outlier handling is transparent, multiple eccentricity distribution families are compared, and the circular-injection experiment is a useful placebo test. The main risks are selection effects in the grazing-transit cut, the post-hoc exclusion of the single outlier, and the limited external validation of the new empirical mass-radius relation that sets the circular-orbit baseline. These concern the core conclusion rather than presentation, so the manuscript needs revision before the dynamical-coolness claim is fully supported.","major_comments":[{"comment":"The grazing-transit cut removes any candidate with more than 50% posterior weight at b > 1 - R_p/R_*, and this cut can preferentially remove eccentric planets. In an eccentric orbit, a circular-orbit fit absorbs the transit-duration change produced by e and omega into a larger impact parameter, so planets transiting near periastron (gamma > 1) are especially likely to be classified as grazing and removed. The precautionary KS test on orbital periods (p = 0.96) does not test the eccentricity dimension, and the injection-recovery experiment injects into the already-selected 17 targets, so it bypasses the selection pipeline entirely. Because 21 of 74 candidates were removed by this cut, the reported mean eccentricity of 0.060 may be an artifact of selection rather than a property of the underlying population. I request a forward-modeling test that injects eccentric populations before the light-curve fits and applies the full selection, or an analytic selection correction; without this, the central 'dynamically cool' claim is not yet established.","section":"Methods, 'Light curve fits'; 'Generating fake circular planets'"},{"comment":"The exclusion of KOI-4087.01 is post-hoc and changes the conclusion: with all 17 planets the exponential model gives mean eccentricity 0.100 (+0.040/-0.031) and the Beta model is favored by AIC, whereas after excluding that planet the exponential model gives 0.060 and is strongly favored. The authors are transparent about reporting both fits, but the abstract and discussion foreground only the 16-planet value. Because the same data are used both to identify the outlier and to define the bulk population, a formal robustness check is needed: for example, a leave-one-out analysis, an outlier p-value under the fitted population model, or a mixture model with a prior on the warm fraction. The headline population mean should either include such a robustness treatment or be explicitly framed as the value conditional on the post-hoc exclusion.","section":"Table 2 and 'Results: Hierarchical Bayesian modelling'"},{"comment":"The circular-orbit baseline stellar density is derived from the Mann mass-luminosity relation together with a new probabilistic mass-radius relation trained on 171 stars from Mann et al. (2015). A systematic offset in this M-R relation would propagate directly into the gamma posteriors and hence into the inferred eccentricities. The external validation against Gaidos et al. (2016) covers 13 Kepler candidates, but only three of the 11 Kepler planets in the final sample (the two KOI-1422 planets and KOI-3284.01) have direct counterparts, and none of the six TESS targets is independently validated. I ask for independent density or radius checks for the final 17 targets where available, or a sensitivity analysis quantifying how large an M-R offset would be needed to move the inferred mean eccentricity by a significant amount.","section":"Methods, 'Stellar inference' and 'Stellar properties'; Supplementary Figure 2"}],"minor_comments":[{"comment":"The Figure 2 caption and contour labels include KOI-7706.01, but Table 1 and the text list only 17 Earth proxies and do not include this object; the label count appears to be 18. This inconsistency must be corrected.","section":"Figure 2 and Table 1"},{"comment":"There are unresolved placeholders in the text: 'Zhu & Dong’s recent review?' and 'RoboAO?' should be replaced with proper citations, and the Data Availability section uses 'this URL' placeholders that must be filled in.","section":"Methods, 'Planet-planet scattering' and 'Light curve fits'"},{"comment":"Several typographical errors should be cleaned up, including 'bear little resemble to Earth', 'Space Space Telescopes', 'we do no calculate TTVs', and the grammatically incomplete sentence beginning 'rather than attempt a colour conversion...'.","section":"Throughout"},{"comment":"Reference 90 duplicates reference 89 (both Goldreich & Soter 1966), and the equation in the tidal circularisation paragraph is attributed to 'ref. 90' while the nearby citation list suggests ref. 89; please clarify which source is intended.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is careful and data-transparent, and I do not see evidence of overclaiming in the sense of hiding the all-17 fit or the outlier treatment. The decisive issue is the unmodeled grazing-transit selection effect, which in my reading genuinely threatens the central conclusion and is not addressed by the current KS test or injection-recovery. The requested selection-bias simulation and a more formal outlier-robustness analysis are within the scope of a revision, so I would not reject; I would ask the authors to re-frame or re-derive the headline claim pending those tests."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"David,\n\nThis paper reports the first eccentricity-distribution measurement for a well-defined sample of Earth-size, Earth-insolation planets around late-type stars. That alone makes it useful. The analysis is careful: homogeneous Mann-relation stellar masses, a new empirical M-R relation, multi-method detrending, HBM with transit-geometry bias, and injection-recovery. The circular injection reproducing the observed mean (0.061 vs 0.060) is a genuinely informative check. The outlier KOI-4087.01 is handled transparently and matches its discovery paper.\n\nThe weak point that matters is sample selection. The grazing-transit cut removes 21 of 74 candidates whose circular-fit posteriors are mostly grazing. A circular model fit to an eccentric transit can absorb the shorter duration as a larger impact parameter, so the cut can preferentially remove high-e planets, especially those transiting near periastron. The period KS test (p=0.96) does not address eccentricity, and the injection-recovery starts from the already-selected 17, so it bypasses the selection pipeline. That means the \"dynamically cool\" conclusion could partly be an artifact of the cut. This is a real limitation, not a fatal one — but it deserves a quantitative test: inject eccentric populations into raw candidates, run the full selection, and check what survives.\n\nOther soft spots are secondary. n=17 is small, and the headline number depends on excluding the one outlier, though the paper is explicit about that. The new M-R relation is a reasonable derivation, but only 13 of the 68 Kepler targets are cross-checked against Gaidos et al., and a systematic offset in stellar density would shift the eccentricities directly. The data and code availability statements still say \"this URL,\" so the promised posteriors and code are not yet reproducible from the arXiv version.\n\nNone of this breaks the core conclusion for the selected sample. The paper is honest about its assumptions, the method is appropriate, and the discussion of model mis-specification is mature. I'd send it to a serious referee — someone who will push on the grazing-cut selection — and I'd expect it to come out acceptable after the selection bias is quantified and the data links are fixed.\n\nFor a reading group, it's worth a seat at the table; I'd probably cite it once the selection question is settled.","headline":"First eccentricity-distribution measurement for a carefully chosen Earth-proxy sample around M/K dwarfs; the near-circular result is probably right, but the grazing-transit cut could bias it and needs an explicit injection test.","tokens_in":34533,"tokens_out":2598,"would_cite":true,"duration_ms":26337,"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":"Earth-size planets around small stars orbit nearly in circles","keywords":["exoplanets","eccentricity","photoeccentric effect","M dwarfs","K dwarfs","transit light curves","hierarchical Bayesian model","Earth-like planets"],"falsifier":"A direct, model-independent measurement of the eccentricity of several of the 17 planets via radial velocities, transit timing variations, or high-precision eclipse timing would falsify the claim: if three or more of the nominally circular sample showed eccentricities above about 0.15, the conclusion of a dynamically cool population would fail. Conversely, detecting a second high-eccentricity Earth proxy among a larger sample would confirm the hypothesized dynamically warm subpopulation, whereas finding none in a sample of tens would strengthen the outlier interpretation.","tokens_in":33525,"feed_emoji":"🪐","tokens_out":3330,"duration_ms":27693,"temperature":0.7,"pith_summary":"This paper measures the orbital eccentricities of 17 transiting planets with Earth-like sizes and instellations around M/K-type stars, using the photoeccentric effect, which infers orbital shape from transit durations. The central claim is that this population is dynamically cool: after excluding one outlier, the favored exponential model yields a mean eccentricity of 0.060 (+0.040/-0.028), and injection-recovery tests show the data are indistinguishable from a purely circular population. The one exception, Kepler-440 b, has eccentricity about 0.40 and may belong to a separate, rarer dynamically warm population. A sympathetic reader should care because these planets resemble Earth in radius and starlight received, and their near-circular orbits mean most experience little eccentricity-driven seasonal climate variation, with consequences for habitability studies and formation theories.","feed_headline":"Earth-size planets around small stars orbit nearly in circles","feed_subtitle":"A 17-planet sample yields mean eccentricity 0.060, with only Kepler-440 b as a warm outlier, easing climate and habitability concerns.","key_machinery":"The photoeccentric effect, a form of asterodensity profiling: comparing the stellar density implied by a transit light curve under the assumption of a circular orbit to an independently measured stellar density. The ratio γ of these densities is sensitive to the orbital eccentricity e and argument of periastron ω, and the paper uses marginal posteriors of log γ as data for a hierarchical Bayesian model (HBM). The HBM fits candidate population distributions for eccentricity (Rayleigh, Tremaine, exponential, Beta) with a geometric transit bias correction, selecting models via AIC and using injection-recovery of fake circular and eccentric populations to calibrate the inference. The stellar densities are derived from the Mann empirical mass-luminosity relation plus a new probabilistic mass-radius relation trained on 171 stars, which is the central external input that anchors the circular-orbit baseline.","core_discovery":"The paper establishes that Earth proxies around late-type stars, the closest observationally accessible analog population to true Earth analogs, have a near-circular eccentricity distribution. Using hierarchical Bayesian modeling of the photoeccentric effect on 17 carefully vetted transiting planets, the authors find that the population, excluding the confirmed planet KOI-4087.01 (Kepler-440 b), is best described by an exponential eccentricity distribution with mean eccentricity 1/λ = 0.060 (+0.040/-0.028), consistent with a purely circular population in injection-recovery tests. Kepler-440 b is a distinct outlier with e = 0.40 (+0.20/-0.12), inferred under a uniform prior, and is argued to be genuinely eccentric rather than a blend or TTV artifact. The paper thus claims that Earth-like planets around the most common star types typically have low eccentricities, supporting formation through smooth disk migration and disfavoring violent planet-planet scattering as the dominant dynamical origin.","pith_inferences":["The inference that the population is indistinguishable from circular rests on an assumed parametric family (exponential); a broader nonparametric approach might reveal structure that these one- and two-parameter models cannot capture, such as a bimodality that the single outlier only hints at.","The new probabilistic mass-radius relation, if applied to a larger sample of transiting planets around late-type stars, could be used to test whether the photoeccentric effect itself is systematically biased by small stellar-density errors, for example by comparing independent asteroseismic or eclipse-based densities on a per-star basis.","One could extend the analysis to TESS-discovered Earth proxies with longer baselines as they accumulate more transits, to push the circular-population test below the current saturation floor of about 0.09-0.15 in mean eccentricity.","The finding implies that dynamically warm Earth proxies, if they exist as a distinct class, may be preferentially found in systems with outer giant planets capable of secular excitation, making them valuable targets for radial-velocity searches for long-period companions."],"forward_implications":["The outer edge of the habitable zone for these planets shifts outward by at most about 2% at 2-σ confidence, because low eccentricity keeps the orbit-averaged flux close to the circular value.","Target selection for atmospheric characterization with JWST is simplified: Earth-like planets around M/K dwarfs mostly avoid eccentricity-induced climate variability and can be treated as near-circular for scheduling and interpretation.","Planet-planet scattering producing the maximal eccentricity of about 0.30 is strongly excluded for the bulk population, favoring formation via disk migration in compact resonance-chain systems or as currently single planets.","The existence of a rare dynamically warm subpopulation, represented by Kepler-440 b, is estimated to comprise less than 21.3% of the ensemble at 2-σ confidence, with a prediction that 34 total Earth proxies would be needed for a 50% chance of finding another member.","If true Earth analogs are a subset of Earth proxies, then Earth-like planets around late-type stars, which dominate the cosmos, most often have near-circular orbits similar to the Earth's own eccentricity of 0.0167."],"supporting_citations":[{"why":"Introduces asterodensity profiling, the method of comparing light-curve-derived stellar density to an independent value, which forms the basis of the eccentricity measurement.","marker":"[13]"},{"why":"Defines the photoeccentric effect and the mathematical mapping between transit durations, stellar density, eccentricity, and argument of periastron.","marker":"[14]"},{"why":"Provides the empirical mass-luminosity relation used to derive stellar masses and the training sample for the new mass-radius relation.","marker":"[21]"},{"why":"Provides the 171 empirically calibrated stars with masses and radii used to train the new probabilistic mass-radius relation.","marker":"[55]"},{"why":"Supplies the hierarchical Bayesian modeling formalism used to infer the ensemble eccentricity distribution.","marker":"[15]"},{"why":"Derives the transit geometric bias correction applied to the eccentricity priors in the HBM.","marker":"[16]"},{"why":"Provides the independent validation of Kepler-440 b's eccentricity and the blended-light checks for several target stars.","marker":"[33]"}],"fun_headline_variants":["Earth twins around small stars orbit almost circularly","Most Earth-size exoplanets around cool stars have near-circular orbits","Photoeccentric survey finds Earth-like planets circle calmly","Kepler-440 b stands out as eccentric planet among Earth-like sample"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The independent stellar densities used as the circular-orbit baseline are unbiased, particularly the new mass-radius relation trained on 171 stars; a systematic offset in these densities would shift the γ ratios and hence the inferred eccentricities directly.","fun_headline_variants_meta":{"raw":{"variants":["Earth twins around small stars orbit almost circularly","Most Earth-size exoplanets around cool stars have near-circular orbits","Photoeccentric survey finds Earth-like planets circle calmly","Kepler-440 b stands out as eccentric planet among Earth-like sample"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000701,"raw_usage":{"total_tokens":3160,"prompt_tokens":937,"completion_tokens":2223,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":553,"completion_tokens_details":{"reasoning_tokens":2152}},"tokens_in":553,"tokens_out":2223,"duration_ms":17506,"temperature":1.0,"reasoning_tokens":2152,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T19:06:46.632948+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A direct, model-independent measurement of the eccentricity of several of the 17 planets via radial velocities, transit timing variations, or high-precision eclipse timing would falsify the claim: if three or more of the nominally circular sample showed eccentricities above about 0.15, the conclusion of a dynamically cool population would fail. Conversely, detecting a second high-eccentricity Earth proxy among a larger sample would confirm the hypothesized dynamically warm subpopulation, whereas finding none in a sample of tens would strengthen the outlier interpretation.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the 171 empirically calibrated stars with masses and radii used to train the new probabilistic mass-radius relation."}],"review_version":1}