{"id":"dfa0310a-efc3-432e-9331-ff3d908ccf84","arxiv_id":"2509.10136","paper_version":1,"verdict":"ACCEPT","confidence":"HIGH","novelty_score":6.0,"correctness_risk":"low","formal_verification":"none","parameter_count":2,"one_line_summary":"TOI-1203 hosts four planets, including two transiting planets with precisely measured masses and radii, around a very old, alpha-enhanced thick-disk star.","lead":"Astronomers used HARPS radial velocities and CHEOPS photometry to confirm one known planet around the bright star TOI-1203 and discover three additional ones, yielding a four-planet system. The star is old, metal-poor, and alpha-enriched, likely a member of the Galaxy's thick disk, so the system offers a benchmark for early planet formation.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"No significant objection identified: the RV-only signals (13.1 d and 204.6 d) are the key risk, but the evidence is strong and the residual gap is testable.","rationale":"The reader's weakest_assumption correctly identifies the planetary interpretation of the two RV-only signals as the most load-bearing element. I reach the same conclusion, but after reading the full analysis I do not find a concrete flaw that should change the verdict. The paper addresses the main confounders explicitly: FAP bootstrap limits, absence of activity-indicator counterparts, the Th-Ar instrumental-profile analysis, the alias structure of the FWHM signal, and the lack of an RV counterpart to the 615 d FWHM periodicity. The transiting planets b and d are independently supported by TESS and CHEOPS, and the stellar companion is shown to have negligible dynamical effect. The only residual gap is that a low-amplitude RV signal (c) was selected through pre-whitening under a white-noise null; a GP or cross-pipeline re-analysis would either confirm or refute that gap, but the current evidence is well within normal standards for a discovery paper. I therefore keep the ACCEPT verdict unchanged.","tokens_in":42634,"tokens_out":10175,"duration_ms":123704,"concrete_test":"Re-run the full joint fit of Sect. 9 on the published TERRA RVs with a quasi-periodic Gaussian-process noise term (amplitude and timescale free) replacing the white jitter, and compare to the white-noise 4-Keplerian model via ΔlnZ. If K_c and K_e remain >3σ and the GP component is not preferred by ΔlnZ > 5, the white-noise assumption is adequate and the planet claims are robust; if the GP absorbs either signal, the pre-whitening FAPs are overconfident.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The four-planet claim depends most heavily on the two RV-only signals, TOI-1203 c (K_c = 1.62±0.14 m/s, P_c ≈ 13.08 d) and TOI-1203 e (K_e = 5.02±0.17 m/s, P_e ≈ 204.6 d), which lack transit confirmation. The paper argues convincingly that these are not stellar activity: the star is very inactive (log R'_HK = −4.998, vsini = 1.4 km/s, no rotation signal), and neither signal has a counterpart in BIS or log R'_HK periodograms (Sect. 4). The 204.6 d signal is also carefully separated from the 230 d alias of the 615–629 d instrumental FWHM variation: the FWHM peak at 230 d disappears when the 615 d signal is removed, and the RVs show no peak near 615 d. The main residual risk is methodological rather than empirical: the significance of the 13.1 d signal in particular is established through pre-whitening with bootstrap FAPs that assume white noise (Sect. 4), while the final fit uses only a white jitter term (Sect. 9). For a 1.62 m/s signal sitting above a 0.83 m/s jitter, unmodeled correlated noise could in principle affect the detection significance. I do not see evidence that this has happened, but it is the one place where a standard robustness check would materially increase confidence.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports the discovery and characterization of a four-planet system around the bright, old, metal-poor G3V star TOI-1203. Using 190 HARPS RVs, TESS and CHEOPS photometry, and a joint MCMC analysis, the authors confirm the previously known transiting sub-Neptune TOI-1203 d (P≈25.5 d, M=7.39±0.62 M⊕, R=2.918±0.045 R⊕), discover and confirm a transiting super-Earth TOI-1203 b (P≈4.16 d, M=3.51±0.33 M⊕, R=1.520±0.045 R⊕), and report two RV-only planets: TOI-1203 c (P≈13.08 d, M sin i=5.46±0.51 M⊕) and TOI-1203 e (P≈204.6 d, M sin i=42.10±1.8 M⊕, e=0.152±0.029). A stability analysis shows that configurations consistent with the data can be stable over Gyr timescales, and an interior-structure analysis of b and d is presented. The paper also identifies a ~615–630 d systematic in the HARPS CCF FWHM, traced to Th-Ar line widths, and attributes it to instrumental profile variations with no counterpart in the RVs.","tokens_in":43001,"tokens_out":4213,"duration_ms":48794,"significance":"If the detections hold, this is a valuable addition to the small sample of precisely characterized multi-planet systems around very old, α-enhanced thick-disk stars. The two transiting planets have masses and radii measured to better than ~10% and ~3%, respectively, placing them on the mass–radius diagram with clear compositional implications. The RV-only planets, especially the 13.1 d signal at K≈1.6 m/s, are the weakest link, and the paper would benefit from a correlated-noise robustness check. The HARPS instrumental-profile finding is an important cautionary result for precision-RV programs. Strengths include the large homogeneous HARPS dataset, the independent CHEOPS confirmation of TOI-1203 b, the use of ancillary activity indicators, the bootstrap FAP calculations, and the explicit forward stability and interior-structure checks that use the fitted parameters as inputs rather than as predictions.","major_comments":[{"comment":"The two RV-only signals (TOI-1203 c at 13.08 d with K_c=1.62±0.14 m/s, and TOI-1203 e at 204.6 d) are load-bearing for the four-planet claim. Their detection significance is established through pre-whitening with bootstrap FAPs that assume white noise, and the final fit models all noise with a single white jitter term (σ_HARPS=0.83±0.10 m/s). For a signal whose amplitude is only ~2× the jitter, unmodeled correlated noise could inflate the significance. I request a robustness check, e.g., a joint fit that includes a Gaussian-process or moving-average term for the RVs, or an injection-recovery test with red-noise residuals. This would materially increase confidence in planets c and e.","section":"Sects. 4 and 9; Table B.2"},{"comment":"The TESS Sector 36 transits of TOI-1203 b are excluded 'due to the lack of a detectable transit signal' in that sector. This is a post-hoc data selection that could bias the transit parameters and ephemeris if the non-detection is due to an unmodeled systematic rather than noise. Since CHEOPS confirms the transit near the same epoch, the exclusion likely does not affect the planet's existence, but the paper should quantify the consistency, e.g., by performing an injection-recovery test in Sector 36 or by modeling the Sector 36 data with a high-noise term.","section":"Sect. 9 and Sect. 5"}],"minor_comments":[{"comment":"The reported RV semi-amplitude for TOI-1203 d is listed as K_d=1.74±0.014 m/s. Given the values for the other planets and the mass uncertainty, the error bar is likely 0.14 m/s, not 0.014. Please check and correct.","section":"Table B.2"},{"comment":"The text 'from 5 January to 2 March 2026, 2025.1' contains a stray '2025.1'; the intended date should be cleaned up.","section":"Sect. 2"},{"comment":"'Adopting the LRS determination' should read 'LSR determination'.","section":"Sect. 8.5"},{"comment":"Typo: 'Markow chains' should be 'Markov chains'.","section":"Sect. 9"}],"recommendation":"major_revision","confidential_remarks":"This is a strong discovery paper with high-quality data and a careful analysis. The central four-planet claim is defensible, but it rests on two RV-only signals; a correlated-noise robustness check is needed to rule out the main alternative interpretation. The Sector 36 exclusion is a secondary but legitimate concern. I do not see grounds for rejection, and the manuscript fits the journal's scope well. The HARPS IP finding is a useful ancillary result."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this is a thorough, well-executed follow-up that turns a single TESS candidate into a four-planet system around a genuinely interesting star. If you care about planet formation in the early galaxy, the radius valley in old populations, or what intensive RV follow-up of TESS targets returns, it is worth your time.\\n\\nWhat is actually new: the 4.2-day super-Earth b (M=3.51±0.33 M⊕, R=1.52±0.05 R⊕), the 13.1-day c (M sin i=5.46±0.51 M⊕), and the 204.6-day eccentric e (M sin i=42.1±1.8 M⊕, e=0.152±0.029) are all new; planet d now has a real mass and a refined radius (7.39±0.62 M⊕, 2.918±0.045 R⊕). The star is a nice find: 12.5 Gyr, [α/Fe]=0.21, thick-disk membership from kinematics and chemistry. The 615-day HARPS FWHM signal, traced into the Th-Ar line widths, is a useful instrumental result for the precision-RV community.\\n\\nWhat is solid: the detections are well supported. 190 HARPS RVs, bootstrap FAPs below 0.1% for all four signals, and no counterparts in BIS, log R'HK, or FWHM periodograms. CHEOPS independently confirms the 4.2-day transit. The handling of the 615-day FWHM variation is careful—the 230-day peak is correctly identified as a one-year alias that disappears when the 615-day signal is removed. The joint MCMC is standard but transparent, and the RVs and photometry go to CDS in machine-readable form.\\n\\nSoft spots: the two RV-only planets carry the main risk. Planet c's K=1.62±0.14 m/s sits not far above the fitted jitter of 0.83 m/s, and its significance rests on pre-whitening with bootstrap FAPs that assume white noise. I see no evidence that correlated noise is faking it—the star is extremely inactive and the activity indicators are clean—but a red-noise robustness check would make the 13.1-day signal bulletproof. The missing Sector 36 transit of planet b is plausibly explained as background noise but never fully closed. Minor: K_d in Table B.2 appears to be 1.74±0.014, presumably ±0.14, and \"one of the earliest planetary systems\" overstates what a 12.5±~1.3 Gyr age supports.\\n\\nBottom line: the central argument holds. Nothing here looks like a fitting artifact or an overinterpreted signal. A referee will have small things to tighten, not a load-bearing flaw. This paper deserves serious review and will be useful to people working on old-star architectures and small-planet composition.","headline":"Solid characterization paper: three new planets around an old thick-disk star, two with precisely measured masses and radii; the two RV-only planets are the main residual risk, but the evidence is strong.","tokens_in":44222,"tokens_out":3308,"would_cite":true,"duration_ms":33754,"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":"Four planets orbit a 12.5-billion-year-old thick-disk star, the paper shows.","keywords":["four-planet system","super-Earth","sub-Neptune","radial velocity","transit photometry","thick disk","stellar abundances","dynamical stability"],"falsifier":"Two more years of high-precision radial velocities tracking the 204.6-day signal through at least two additional cycles: if it is not coherent as a single Keplerian, or if modeling the instrument-profile variation removes it, the planetary interpretation of TOI-1203 e collapses. A secondary check would be detecting transits of c or e, which the paper argues are unlikely but which would settle their geometry.","tokens_in":42548,"feed_emoji":"🪐","tokens_out":6281,"duration_ms":64969,"temperature":0.7,"pith_summary":"The paper reports that the bright G3V star TOI-1203, a 12.5-billion-year-old, alpha-element-enhanced member of the galactic thick disk, hosts four planets: a transiting super-Earth on a 4.2-day orbit, a non-transiting super-Earth on a 13.1-day orbit, the previously known transiting sub-Neptune on a 25.5-day orbit (now with a measured mass), and a non-transiting eccentric Neptune-mass planet on a 204.6-day orbit. Masses and radii of the two transiting planets are measured to 8-9% precision, and dynamical integrations find configurations stable over billion-year timescales. If correct, this is one of the oldest known multi-planet systems, with implications for when rocky planets could form in the metal-poor early galaxy. The paper also identifies a ~615-day variation in the HARPS instrumental profile that leaves no detectable imprint on the radial velocities, a cautionary result for ultra-precise Doppler surveys.","feed_headline":"Four planets found around a 12.5-billion-year-old star","feed_subtitle":"HARPS and CHEOPS data reveal a rocky super-Earth and an eccentric Neptune joining an old, metal-poor thick-disk system.","key_machinery":"The analysis rests on a joint Markov-chain Monte Carlo fit of TESS and CHEOPS transit light curves together with HARPS radial velocities modeled as four Keplerians, combined with iterative pre-whitening of GLS periodograms to isolate the Doppler signals. The long-period systematic in the HARPS line-profile FWHM is diagnosed by comparing the CCF FWHM against the FWHM of Th-Ar calibration lines, identifying a ~615-day instrumental profile variation. Dynamical stability is assessed with global frequency analysis maps and long symplectic integrations, and internal compositions are inferred from mass-radius modeling.","core_discovery":"TOI-1203 is a four-planet system. The 25.5-day transiting sub-Neptune previously flagged by TESS is spectroscopically confirmed, with its mass determined (7.39±0.62 M⊕) and radius refined (2.918 R⊕). A new transiting super-Earth, TOI-1203 b, is confirmed by CHEOPS photometry with mass 3.51 M⊕ and radius 1.52 R⊕. Two additional Doppler signals at 13.1 and 204.6 days are attributed to planets with minimum masses 5.46 and 42.10 M⊕; the outer planet is eccentric (e=0.152). The host is an old (12.5 Gyr), metal-poor, alpha-enhanced thick-disk star. Stability maps show the system is stable for Gyr, sits near but not inside mean-motion resonances, and has the pericenters of c and d anti-aligned. A l","pith_inferences":["If the 204.6-day signal is confirmed as a planet, TOI-1203 will be a reference for how early-galaxy rocky planets form, since the system assembled when the universe was about 1.3 Gyr old.","The stability analysis maps out stable niches between b and c and between d and e; additional RV monitoring could test whether those niches are empty or occupied by smaller companions.","The Th-Ar line-width diagnostic used here could be reapplied to archival HARPS data to flag long-period RV signals that coincide with instrument-profile variations, potentially reclassifying some published planet candidates."],"forward_implications":["TOI-1203 b becomes one of the rare small planets whose mass and radius are both known to better than ~10%, placing it in the rocky/silicate regime of the mass-radius diagram.","The system straddles the radius valley, with a rocky super-Earth and a volatile-rich sub-Neptune orbiting the same old star, offering a test of how wide binaries and stellar age affect the valley's location.","The near-but-not-exact period commensurabilities (3:1, 2:1, 8:1) and the anti-aligned pericenters of c and d provide a benchmark for models of migration, tidal damping, and secular evolution in ancient systems.","The detected ~615-day instrumental profile variation, with no RV counterpart, shows that symmetric profile changes can hide in line-width diagnostics; monitoring IP shape is therefore essential for RV surveys aiming at 10 cm/s precision."],"fun_headline_variants":["Four planets found around 12.5-billion-year-old star","Old thick-disk star TOI-1203 hosts four planets","Super-Earth and eccentric Neptune join ancient system","HARPS and CHEOPS confirm four planets around ancient star","12.5 Gyr star from the thick disk has four planets"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The 13.1-day and 204.6-day radial-velocity signals are genuine planets, not artifacts of the pre-whitening procedure, stellar activity, or the ~615-day instrumental profile drift whose 230-day alias sits within the frequency resolution of the 204.6-day signal.","fun_headline_variants_meta":{"raw":{"variants":["Four planets found around 12.5-billion-year-old star","Old thick-disk star TOI-1203 hosts four planets","Super-Earth and eccentric Neptune join ancient system","HARPS and CHEOPS confirm four planets around ancient star","12.5 Gyr star from the thick disk has four planets"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000251,"raw_usage":{"total_tokens":1575,"prompt_tokens":1107,"completion_tokens":468,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":851,"completion_tokens_details":{"reasoning_tokens":381}},"tokens_in":851,"tokens_out":468,"duration_ms":5247,"temperature":1.0,"reasoning_tokens":381,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-04T18:05:36.343886+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Two more years of high-precision radial velocities tracking the 204.6-day signal through at least two additional cycles: if it is not coherent as a single Keplerian, or if modeling the instrument-profile variation removes it, the planetary interpretation of TOI-1203 e collapses. A secondary check would be detecting transits of c or e, which the paper argues are unlikely but which would settle their geometry.","supporting_citations":[],"review_version":1}