{"id":"a52f2c91-7c24-4ae7-8bc0-b739955a532b","arxiv_id":"2505.00898","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":9,"one_line_summary":"HD 35843 hosts a 9.90-day non-transiting planet (minimum mass 5.84 M⊕) and a 46.96-day transiting sub-Neptune (radius 2.54 R⊕, mass 11.32 M⊕).","lead":"Astronomers report two planets around the Sun-like star HD 35843: a close, non-transiting super-Earth and a cooler, transiting sub-Neptune on a 47-day orbit. The system is bright enough that the outer planet may be studied with the James Webb Space Telescope, adding a rare data point for temperate sub-Neptunes.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 9.9-day planet b signal is not fully secured because the final fit excludes PFS RVs that make Pb bimodal, and a 27-day residual activity peak remains; a joint activity-aware fit is needed.","rationale":"The reader's weakest assumption correctly identifies the 9.9-day RV signal and the exclusion of the PFS data as the soft spot in the paper. I partly agree: my concern also centers on the planet b detection, but I place more weight on the post hoc exclusion of PFS and the bimodal Pb posterior in the alternative fit, rather than on activity indicators alone, since the star appears inactive and the activity-correlation checks are reasonably thorough. The transiting planet c is well validated by TESS photometry, ground-based follow-up, high-resolution imaging, and ESPRESSO RVs, so the central claim is not invalidated. However, the inner planet's existence is conditional on the 9.9-day signal surviving a joint fit that includes PFS and a flexible activity model. Since the paper already provides an alternative fit with PFS and clearly discloses the exclusion, the appropriate disposition remains conditional acceptance pending that test. Therefore I do not change the reader's verdict, but I would make the requested joint fit an explicit condition rather than a suggestion.","tokens_in":36449,"tokens_out":3762,"duration_ms":41506,"concrete_test":"Re-do the Section 3.4 allesfitter fit using both ESPRESSO and PFS RVs, adding a shared sinusoid or Gaussian-process term for stellar activity with a period prior of 20-30 d, and compute the Bayes factor between models with and without a 9.9 d Keplerian. Also record whether the Pb posterior becomes unimodal. If K_b remains above 5σ and Pb is unimodal with the activity term, the planet is confirmed; if the 9.9 d signal is absorbed or Pb remains bimodal, planet b should be reported as a candidate pending additional RVs.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim that HD 35843 hosts an inner, non-transiting 9.9-day planet rests entirely on the ESPRESSO radial velocities. Two features make that claim less secure than the transiting planet c. First, the star shows a strong rotation-period signature in the bisector span at 25.49 d (FAP 1e-8), and after removing both fitted planets the residual RVs still show a peak at 26.95 d with FAP 0.02 (Section 3.1.1, Figure 10). The 9.9-day signal has K = 1.81 ± 0.25 m/s and is therefore asserted against a not-fully-modeled activity background. Second, and more concretely, Section 3.4 states that the PFS RVs are excluded from the global fit because they make the period of planet b bimodal; the alternative fit with PFS shown in Appendix D still has a bimodal Pb posterior. PFS is an independent dataset with 18 epochs and ~1 m/s precision, so excluding it post hoc removes the most direct check on whether the 9.9-day period is unique or an alias. The activity-indicator correlations and stacked BGLS periodogram argue against a pure activity origin, so this is not a fatal flaw, but the planetary interpretation of planet b is exactly the assumption that needs explicit testing before the two-planet architecture is treated as established.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports the discovery and characterization of two planets around the metal-poor Sun-like star HD 35843 (TOI 4189). The outer planet, HD 35843 c, is a transiting sub-Neptune with P = 46.9622 d, R = 2.54 R⊕, M = 11.32 M⊕, and e = 0.15, validated through TESS photometry, ground-based follow-up, speckle imaging, and ESPRESSO radial velocities, with a triceratops false-positive probability of 0.05%. The inner planet, HD 35843 b, is inferred from ESPRESSO RVs with P = 9.90 d and a minimum mass of 5.84 M⊕, and is not observed to transit. The authors combine TESS and ESPRESSO data in a joint allesfitter fit, explore model scenarios with BIC/AIC, check activity indicators, and discuss composition and atmospheric prospects.","tokens_in":36824,"tokens_out":4425,"duration_ms":47813,"significance":"If both planets are real, the system is valuable: HD 35843 c is a bright (V = 9.4), temperate sub-Neptune with a precise mass and radius, adding to the sparse population of long-period transiting sub-Neptunes with well-measured masses. The validation of planet c is thorough and community-oriented, and the TSM and equilibrium temperature make it a plausible JWST target. Planet b, if confirmed, would make the system one of only a few with a non-transiting inner planet interior to a transiting sub-Neptune, with implications for system architecture and formation. The analysis is generally careful, with explicit activity checks, injection-recovery tests, and an appendix with the alternative fit including PFS. The main weakness is the security of planet b, whose detection rests on a single instrument and the post-hoc exclusion of an independent dataset.","major_comments":[{"comment":"The exclusion of the PFS radial velocities from the final joint fit is a load-bearing step for the 9.9-day planet b claim. The text states that PFS data are excluded because they 'result in a bimodal posterior for the period of planet b'; Appendix D shows that the joint fit with PFS still yields a bimodal Pb posterior (printed median 9.935 d over a 9.75-10.05 d prior, with two modes). Since PFS is an independent 18-epoch dataset with ~1 m/s precision, the bimodality indicates that the 9.9-day period is not uniquely determined when a second, independent dataset is included. Please provide a periodogram and a joint model of the ESPRESSO and PFS RVs (with and without an activity component), and discuss whether the 9.9-day signal is an alias or is genuinely present in both datasets. The current treatment amounts to removing the dataset that challenges the claimed period, and that is not sufficient support for the discovery claim.","section":"Section 3.4, Appendix D"},{"comment":"A ~25-27 d stellar activity signal is detected in the bisector span (25.49 d, FAP 1e-8) and remains in the RV residuals at 26.95 d with FAP 0.02 after subtracting both planets, yet the RV fits model only white noise (jitter) plus the two Keplerian signals. The 9.9-day signal has K = 1.81 ± 0.25 m/s, only a few times the expected activity-induced RV amplitude for a slowly rotating G star. To secure the planetary interpretation of the 9.9-day signal, the authors should perform a joint fit that includes a quasi-periodic Gaussian-process activity model (or at least a sinusoid at the adopted rotation period) and show that the 9.9-day Keplerian remains stable in period, amplitude, and significance. The checks against activity indicators are useful but do not rule out a non-sinusoidal or harmonic activity signal that could project onto the 9.9-day period.","section":"Section 3.1.1, Section 3.3.1, Section 3.4"},{"comment":"The model comparison in Table 2 prefers the two-planet flat model over the two-planet linear-trend model by ΔBIC = 2.55 but by only ΔAIC = 0.94, which is marginal evidence against a linear trend; the text states the preference is 'nearly indistinguishable' between the flat and linear two-planet models. This is not itself a problem, but the derived parameter tables and discussion should note that the trend is not strongly constrained and that omitting a trend could slightly bias Kb or Kc. A sentence in Section 3.3.1 or Section 3.4 would suffice.","section":"Section 3.3.1, Table 2"},{"comment":"The discussion states a minimum mass for HD 35843 b of 5.47 ± 0.82 M⊕, which is inconsistent with the abstract, Table 4, and Section 5 (5.84 ± 0.84 M⊕). Because this is the only reported parameter for planet b that appears in multiple places, the inconsistency should be corrected before publication.","section":"Section 4"}],"minor_comments":[{"comment":"The caption says 'Ground-based photometry of HD 35843 b', but the transits shown belong to HD 35843 c; the figure and text refer to the 46.96-day transiting planet. Please correct the caption.","section":"Figure 3 caption"},{"comment":"The phrase 'among the coolest ~5% of planets discovered by TESS' lacks a quantitative definition or citation; please specify the comparison sample (e.g., TESS confirmed planets with measured radii) and provide the percentile calculation.","section":"Abstract"},{"comment":"The inner planet's eccentricity is fixed to zero in the global fit (√eb cosωb = √eb sinωb = 0), but a test with a free eccentricity for planet b is not reported. Given the low Kb, an eccentric solution could affect the period and mass; please report such a test or justify why circularity is a safe assumption.","section":"Section 3.4, Table 3"},{"comment":"The triceratops FPP is quoted as 0.05 ± 0.01 %, but the sentence immediately before states an NFPP of (2.7 ± 0.7) × 10−8 and then says 'We calculate an FPP of 0.05 ± 0.01 %'. It would be clearer to define FPP and NFPP in the text, since the former is the more standard validation metric.","section":"Section 3.2"},{"comment":"The PFS RVs are listed as relative velocities with an arbitrary zero point; because the final fit excludes them, the table would benefit from a note stating the zero-point convention and whether the absolute velocities were adjusted to a common barycentric frame.","section":"Table A1"}],"recommendation":"major_revision","confidential_remarks":"The central issue is the planetary status of HD 35843 b. The transiting planet c is well validated, but the 9.9-day signal rests entirely on ESPRESSO, and the exclusion of the PFS dataset that introduces a bimodal Pb posterior is a serious concern that the authors must address head-on. If a joint ESPRESSO+PFS fit with an activity model still supports a single 9.9-day period, the paper would be acceptable for publication; otherwise, the discovery claim for planet b should be downgraded to a 'candidate' or 'tentative' signal. The paper is otherwise well-organized and the data products are valuable."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Bottom line: HD 35843 c is a solid, well-characterized long-period sub-Neptune. HD 35843 b is plausible but not fully secured, and the paper's own handling of the PFS RVs is the reason.\n\nThe transiting planet c is a genuinely useful addition: a 46.96-day, 2.54 R⊕ sub-Neptune with a 3-σ mass of 11.3 M⊕ around a bright (V=9.4) metal-poor Sun-like star. The validation is thorough — TESS and follow-up photometry, high-resolution speckle imaging, triceratops FPP at 0.05%, and ESPRESSO RVs. The RV model comparison is careful, with activity-indicator checks and a stacked BGLS that behaves properly for a coherent signal. I also credit the authors for reporting the alternative fit with PFS in the appendix, even though they do not adopt it. And the citizen-science identification of the transit is a nice touch.\n\nThe soft spot is the inner planet. The 9.9-day signal is only K = 1.8 m/s, and the star shows rotation-scale variability at 25-27 days in the bisector and in the residual RVs (FAP 0.02). The authors exclude the PFS RVs from the global fit because they make Pb bimodal, and the appendix fit with PFS still shows a bimodal Pb posterior. That is a post hoc choice that removes the most independent check on a low-amplitude signal living in the same period range as stellar activity. The activity indicators at 9.9 days are clean and the signal grows with observations, so this is very likely a real planet, but the current treatment does not close the case. A joint fit that models the activity with a Gaussian process, alongside a clearer statement of what the PFS data do and do not rule out, would make the claim load-bearing rather than assumed.\n\nTwo minor points. The TSM of ~25 makes 'promising atmospheric target' a bit generous; toning that down would be more honest. And the potential TTVs rest on partial ground-based transits; the paper already labels them as uncertain, which is appropriate.\n\nThis is not a fatal flaw. The two-planet architecture is probably right, and planet c is on solid ground. The paper deserves a serious referee; I would accept with revision and ask the authors to address the PFS exclusion directly.","headline":"HD 35843 c is a solid, well-characterized long-period sub-Neptune; HD 35843 b is plausible but the paper's exclusion of PFS RVs leaves the inner planet less certain than advertised.","tokens_in":37602,"tokens_out":3356,"would_cite":true,"duration_ms":33623,"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":"HD 35843 hosts two planets: a transiting 46.96-day sub-Neptune and a non-transiting 9.90-day super-Earth.","keywords":["exoplanets","sub-Neptune","super-Earth","transit photometry","radial velocities","TESS","planet validation","atmospheric characterization"],"falsifier":"A decisive test is to add more ESPRESSO radial velocities over a longer baseline and include the independent radial-velocity data in a single joint fit: if the 9.9-day signal does not stay phase-coherent with one well-determined period near 9.90 days, or if its amplitude tracks the bisector or line-width activity indicators, then planet b is not established.","tokens_in":36260,"feed_emoji":"🪐","tokens_out":13682,"duration_ms":118245,"temperature":0.7,"pith_summary":"The paper sets out to establish that the metal-poor Sun-like star HD 35843 hosts two planets: a temperate transiting sub-Neptune on a 46.96-day orbit and an inner, non-transiting super-Earth-mass planet on a 9.90-day orbit. A joint analysis of TESS photometry and high-precision radial velocities gives the outer planet a radius of $2.54\\,R_\\oplus$, a mass of $11.32\\,M_\\oplus$, and a slightly eccentric orbit, while the inner signal has a minimum mass of $5.84\\,M_\\oplus$. If correct, the system joins the small sample of well-characterized long-period, temperate sub-Neptunes bright enough for atmospheric follow-up, and it provides a rare architecture in which the inner planet does not transit.","feed_headline":"Sun-like star hosts a temperate sub-Neptune and an inner super-Earth","feed_subtitle":"A 46.96-day transiting world with a measured mass joins the rare cool sub-Neptunes bright enough for JWST follow-up.","key_machinery":"The central object is a two-planet Keplerian model constrained by the transits of planet c and the Doppler wobble of both planets. The load-bearing technique is a joint nested-sampling fit of the TESS light curve with the ESPRESSO radial velocities, supported by a Lomb-Scargle periodogram and a stacked periodogram that show the 9.9-day signal grows stronger as more data are added and does not correlate with stellar activity indicators. False-positive scenarios for the transiting planet are excluded with ground-based photometry, high-resolution imaging, and a statistical validator that returns a false-positive probability of about $0.05\\%$.","core_discovery":"The paper reports the discovery and confirmation of two planets around HD 35843 (TOI 4189), a metal-poor G dwarf. The outer planet, HD 35843 c, transits with period $P=46.9622$ d, radius $R=2.54\\,R_\\oplus$, mass $M=11.32\\,M_\\oplus$, and eccentricity $e=0.153$; the inner planet, HD 35843 b, is detected only in radial velocities with period $P=9.8991$ d and minimum mass $M\\sin i=5.84\\,M_\\oplus$. The outer planet's bulk density of $3.80$ g/cm$^3$ places it in the degenerate region between a rocky planet with a substantial hydrogen envelope and a water world, and its equilibrium temperature of about $480$ K makes it one of the coolest sub-Neptunes found by TESS.","pith_inferences":["The bimodal period for planet b that appears when the independent radial-velocity data are included is a warning sign; if future data do not sharpen the 9.9-day period into a single coherent solution, the inner planet could turn out to be activity or an alias, leaving HD 35843 as a one-planet system.","If the apparent transit-timing variations in the ground-based partial transits are real, they imply a third body in the system; full transits from Sectors 87 and 95 could confirm this and constrain the perturber's mass.","A rocky, non-transiting b with $M\\sin i\\approx5.8\\,M_\\oplus$ would put the system on both sides of the radius valley, offering a single-star test bed for how super-Earths and sub-Neptunes form in the same disk.","The host's low metallicity suggests that temperate sub-Neptunes can form around metal-poor stars; a targeted search for such planets around other metal-poor FGK stars would test how common this population is."],"forward_implications":["HD 35843 c joins the small set of long-period ($P>40$ d) transiting sub-Neptunes with a well-measured mass orbiting a bright host star, making it a high-value target for atmospheric characterization.","The measured density of $3.80$ g/cm$^3$ means the planet's composition is ambiguous between a rocky world with a hydrogen envelope and a water world; only atmospheric spectra can break that degeneracy.","If planet b truly does not transit, HD 35843 becomes one of only six known systems with a non-transiting inner planet and a transiting outer sub-Neptune, an architecture that may preserve a record of past dynamical instability.","Upcoming TESS re-observations in Sectors 87 and 95 can test whether b transits and can check the apparent transit-timing variations of c."],"supporting_citations":[{"why":"identified the 46.96-day transit signal through the citizen-science search that first flagged HD 35843 c as a candidate.","marker":"Eisner et al. 2021"},{"why":"produced the SPOC TESS light curves used for transit detection and validation.","marker":"Jenkins et al. 2016"},{"why":"describes the ESPRESSO spectrograph whose 70 radial velocities carry the two-planet detection and mass measurements.","marker":"Pepe et al. 2021"},{"why":"supplies the radial-velocity modeling package used to compare one- versus two-planet models and select the two-planet flat model.","marker":"Fulton et al. 2018"},{"why":"provides the joint photometric and radial-velocity fitting framework that yields the adopted system parameters.","marker":"Günther & Daylan 2021"},{"why":"gives the statistical validator used to compute the false-positive probability for the transiting planet.","marker":"Giacalone & Dressing 2020"},{"why":"defines the transmission spectroscopy metric used to rank HD 35843 c as a follow-up target.","marker":"Kempton et al. 2018"},{"why":"supplies the interior-model tool used to infer the water-rich composition of planet c.","marker":"Baumeister & Tosi 2023"}],"fun_headline_variants":["Cool sub-Neptune and super-Earth orbit Sun-like star","Temperate sub-Neptune joins inner super-Earth at HD 35843","Two new planets: a cool sub-Neptune and a super-Earth","Cool sub-Neptune with mass measured around HD 35843"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the 9.9-day radial-velocity wobble assigned to HD 35843 b comes from an orbiting planet rather than from stellar activity or an alias of the observing window; the paper's own analysis leaves a residual ~27-day peak with false-alarm probability 0.02, and adding independent radial-velocity data makes the period of planet b bimodal, so this is the premise that would collapse the two-planet claim.","fun_headline_variants_meta":{"raw":{"variants":["Cool sub-Neptune and super-Earth orbit Sun-like star","Temperate sub-Neptune joins inner super-Earth at HD 35843","Two new planets: a cool sub-Neptune and a super-Earth","Cool sub-Neptune with mass measured around HD 35843"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000263,"raw_usage":{"total_tokens":1661,"prompt_tokens":1069,"completion_tokens":592,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":685,"completion_tokens_details":{"reasoning_tokens":511}},"tokens_in":685,"tokens_out":592,"duration_ms":5074,"temperature":1.0,"reasoning_tokens":511,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-16T04:32:04.990401+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A decisive test is to add more ESPRESSO radial velocities over a longer baseline and include the independent radial-velocity data in a single joint fit: if the 9.9-day signal does not stay phase-coherent with one well-determined period near 9.90 days, or if its amplitude tracks the bisector or line-width activity indicators, then planet b is not established.","supporting_citations":[],"review_version":1}