{"id":"e767ff5f-c49d-40ef-be9e-daf51e2c01ab","arxiv_id":"2501.04083","paper_version":3,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"CSST and Roman should detect Earth-mass to Moon-mass satellites around free-floating planets in microlensing surveys, with Roman more sensitive than CSST.","lead":"The authors simulated how often the Chinese Space Station Telescope and the Roman Space Telescope could spot moons orbiting free-floating planets in microlensing events. They find Earth-mass moons around Neptune-class free-floating planets should be detectable over a wide range of separations, and Roman is more sensitive than CSST, especially for faint red dwarf sources.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Section 4's Hill-radius threshold for Neptune-class FFPs is off by ~90x; corrected, the claim that the whole Neptune detection zone lies within the Hill radius fails for ejection from a_planet ~1 AU, narrowing the physically plausible parameter space for the headline exomoon detections.","rationale":"The reader's CONDITIONAL verdict is appropriate: the central detection-efficiency claim is supported by standard simulation methodology and the correction of the earlier Roman estimate is well argued. The Hill-radius slip in Section 4 is a real internal error that should be fixed, and it weakens the physical-existence argument more than the manuscript admits, but it does not overturn the feasibility conclusion because the detection maps are conditional on the existence of such systems and remain valid for sufficiently wide ejection orbits. The reader noted the numerical slip but did not treat it as the weakest assumption, which is why my agreement is only partial; the survey-strategy caveat the reader identified is explicitly acknowledged in Section 5, whereas the Hill-radius error is unacknowledged and concretely checkable. On balance, the verdict stays CONDITIONAL rather than moving to ACCEPT or REJECT, so no change to the reader's verdict is needed.","tokens_in":10983,"tokens_out":19504,"duration_ms":183504,"concrete_test":"Recompute r_H/R_E from Eqs. (3)-(4) for the Neptune-class lens using m = 16 M_Earth and the Table 3 Einstein radii, verifying that the equality r_H = R_E occurs at a ~ 1.13 AU (disk) and ~0.79 AU (bulge), not 0.013 and 0.008 AU. If the corrected values hold, re-evaluate the survival statement in Section 4: a satellite at s = 1 (0.03 AU) around a disk Neptune is bound only for a_planet >= ~1.2 AU and satisfies the 0.1 r_H survival threshold only for a_planet >= ~12 AU; the claim that the entire detection zone lies within the Hill radius for typical a >= 1 AU would then be false.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The most load-bearing weak point is the physical-consistency argument in Section 4, specifically Eq. (4). For a Neptune-class lens (m = 16 M_Earth), Eq. (4) gives r_H/R_E = 1.4 (a/1 AU) x 16^(-1/6) = 0.88 a in the disk and 1.26 a in the bulge, so r_H/R_E = 1 at a ~ 1.13 AU (disk) and a ~ 0.79 AU (bulge). The manuscript instead states a = 0.013 (0.008) AU, an error of roughly two orders of magnitude. This is not merely cosmetic: the following sentence uses the erroneous value to conclude that the satellite detection zones for Neptune-class FFPs are entirely within the Hill radius for typical ejection radii >= 1 AU. With the corrected threshold, an Earth-mass satellite at the Einstein radius (r_perp ~ 0.03 AU for a disk Neptune) is outside the Hill radius if the system was ejected from a ~ 1 AU (r_H ~ 0.025 AU), and it satisfies the quoted <= 0.1 r_H survival criterion only for ejection radii >= ~12 AU. Thus the paper overstates the physical parameter space over which detectable Neptune-satellite configurations are expected to survive ejection. The detection-efficiency maps themselves are unaffected, but the link from 'detectable' to 'could exist around ejected FFPs' is weakened.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript presents forward simulations of space-based microlensing observations of free-floating planets (FFPs) with a bound satellite, computing detection efficiency as a function of satellite-to-planet mass ratio q and projected separation s in units of the Einstein radius. The authors model CSST and Roman photometry for G2V and M0V bulge sources and for Earth-mass and Neptune-class lenses in the disk and bulge, using VBBinaryLensing to generate 2L1S light curves and MCMC fits to 1L1S models with a detection threshold of Delta-chi-squared of at least 100. They report that CSST can detect Earth-mass satellites around disk Neptune-class FFPs over roughly a decade of projected separations, with sensitivity down to Moon-mass satellites near s approximately 1, that M-dwarf sources strongly degrade CSST but not Roman sensitivity, and that a previous Roman study by Sajadian and Sangtarash overestimates efficiency by fixing the 1L1S parameters. A final section discusses Roche, Hill, and ejection-survival constraints and the possibility of tidally heated satellites.","tokens_in":1347,"tokens_out":4628,"duration_ms":114100,"significance":"The detection-efficiency calculation is standard, transparent, and carefully executed: the use of free-parameter 1L1S fits rather than fixed-parameter fits is well justified and supported by illustrative examples, and the explicit acknowledgment that the CSST observing strategy is idealized is appropriate. If the efficiency maps are correct, the paper provides the first quantitative CSST exomoon forecast and a useful Roman comparison, with concrete statements about which q-s configurations are detectable. No step in the pipeline equates an output to an input; the survey parameters are externally chosen, so the detection efficiencies are genuine forward-model outputs. The main weakness is in the physical-consistency section: Eq. (4) contains a numerical error that invalidates the claim that the entire Neptune-class detection zone lies within the Hill radius for typical ejection radii, and this weakens the link from detectable configurations to plausibly surviving ejected systems. The forward-model results themselves do not depend on that error.","major_comments":[{"comment":"For a Neptune-class lens (m_p = 16 M_Earth), Eq. (4) yields r_H/R_E = 1.4 (a/1 AU) x 16^(-1/6) approximately 0.88 (a/1 AU) in the disk and r_H/R_E approximately 1.26 (a/1 AU) in the bulge. Setting r_H/R_E = 1 therefore gives a_planet approximately 1.13 AU (disk) and approximately 0.79 AU (bulge), not a_planet = 0.013 (0.008) AU as printed. The following sentence, which concludes that the Neptune-class satellite detection zones lie entirely within the Hill radius for typical ejection radii greater than about 1 AU, is consequently incorrect. For example, an Earth-mass satellite at s approximately 1 around a disk Neptune has r_perp approximately 0.03 AU, which exceeds r_H approximately 0.025 AU for a_planet = 1 AU. The detection-efficiency maps in Figures 4-6 are unaffected, but the physical-consistency argument must be recomputed with the corrected threshold.","section":"Section 4, Eq. (4)"},{"comment":"The statement that most of our detectable satellites around Neptune-class planets will survive under the less-than-or-equal-to 0.1 r_H survival criterion is not supported once Eq. (4) is corrected. For a Neptune at a_planet = 10 AU, 0.1 r_H is approximately 0.025 AU, while the Earth-mass detection zone extends to r_perp approximately 0.1 AU; only a fraction of the efficiency-weighted parameter space satisfies the survival criterion. The paper should quantify the fraction of detectable (s, q) configurations that lie within 0.1 r_H as a function of a_planet and state which ejection radii are consistent with the headline sensitivity claims.","section":"Section 4, last paragraph"}],"minor_comments":[{"comment":"The caption labels the left panel as Earth and the right panel as Neptune, while the body text says the detected regions are significantly larger for Neptune-class FFPs (left) compared to Earth-mass FFPs (right); one of these is reversed.","section":"Figure 3 caption and text"},{"comment":"The phrase 'minimum separations detectable planets by CSST or Roman' should read 'minimum separations detectable by CSST or Roman'.","section":"Section 4, Roche-radius paragraph"},{"comment":"The abstract quotes r_perp approximately 0.02 AU for s approximately 2 around an Earth-mass disk FFP, while Table 3 gives R_E = 0.007 AU, so s approximately 2 corresponds to approximately 0.014 AU; the rounding is loose enough to be misleading.","section":"Abstract and Table 3"},{"comment":"The manuscript does not state availability of simulation code or mock light-curve data; releasing them would materially aid reproducibility of the efficiency maps.","section":"General"},{"comment":"The idealized-strategy caveat is clearly stated, but the quantitative contours in Figures 4 and 5 should be explicitly labeled as upper-bound sensitivities for the assumed CSST cadence, filter, and noise floor.","section":"Section 5"}],"recommendation":"major_revision","confidential_remarks":"The core simulation pipeline and the correction of the Sajadian and Sangtarash comparison are solid and well argued. The Hill-radius error is isolated to the physical-plausibility discussion and is fixable without altering the detection-efficiency calculations. I recommend major revision so that the authors can recompute Section 4, revise the survival claims, and re-scope the headline statements about ejected Neptune-satellite systems."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"You should know this paper gives the first quantitative CSST exomoon detection-efficiency maps for free-floating planets, plus a corrected Roman estimate. The correction of Sajadian & Sangtarash is real: fixing the 1L1S parameters to the 2L1S values inflates sensitivity, and the two worked examples are convincing. The pipeline follows the standard Rhie/Dong method, and the central sensitivity maps are new and usable.\n\nWhat the paper does well: it uses standard detection-efficiency methodology, checks G2V vs M0V sources, disk vs bulge lenses, and nonzero impact parameters. The Roman comparison is framed fairly, and the sensitivity maps are forward-simulation outputs with no circular reasoning. I found the magnification-excess maps and the close/wide degeneracy discussion helpful.\n\nThe soft spots are real but mostly minor, except one that is not. The numerical slip in Eq. (4) is genuine. For a Neptune-class lens (m = 16 M_Earth), Eq. (4) gives r_H/R_E = 0.88 a in the disk, so r_H/R_E = 1 at a ~ 1.1 AU, not 0.013 AU as printed. That invalidates the sentence claiming the satellite detection zones for Neptune-class FFPs are entirely within the Hill radius for typical ejection radii. With the corrected threshold, a detectable Earth-mass satellite at r_perp ~ 0.03 AU lies outside the Hill radius for ejection at 1 AU, and survives the quoted <0.1 r_H criterion only for ejection at ~10 AU. The detection-efficiency maps are unaffected, but Section 4's physical-consistency argument needs to be redone. The other concerns are minor: idealized CSST cadence, a single detection threshold, no released code or data. These are standard caveats, not fatal.\n\nWho gets value from this: observers planning CSST or Roman bulge surveys, and theorists modeling ejection and survival of planet-satellite systems. It deserves a serious referee. Send it out; the referee should check Eq. (4) and the survival discussion in Section 4 carefully.","headline":"A useful forward-simulation feasibility study with a solid Roman correction, but the Hill-radius argument in Section 4 contains a ~90x arithmetic slip that weakens the physical-survival claims for Neptune-class FFPs.","tokens_in":11824,"tokens_out":2004,"would_cite":true,"duration_ms":20123,"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 paper argues that CSST's planned bulge microlensing survey can detect exomoons around free-floating planets, with sensitivity down to Moon-mass satellites for Neptune-class hosts and Earth-mass satellites across a decade of…","keywords":["exomoons","free-floating planets","gravitational microlensing","CSST","Roman Space Telescope","detection efficiency","tidal heating"],"falsifier":"Take the first season of actual CSST bulge data and search short FSPL events for caustic anomalies; if the observed number of Neptune-class FFP events matches current rate estimates but no Moon-mass satellite perturbation appears near the Einstein radius, the predicted detection efficiency is too high. The comparison is also directly testable by re-running the Sajadian & Sangtarash (2023) simulations with free single-lens parameters, which should lower their reported efficiencies toward the values reported here.","tokens_in":10786,"feed_emoji":"🌙","tokens_out":5546,"duration_ms":48486,"temperature":0.7,"pith_summary":"The paper argues that the planned microlensing survey of the Chinese Space Station Telescope can detect satellites (exomoons) orbiting free-floating planets, not just the planets themselves. For a Neptune-class free-floating planet in the Galactic disk with a Sun-like source star, the simulated sensitivity reaches down to Moon-mass satellites near the Einstein radius and covers a decade of projected separations for Earth-mass satellites. This matters because exomoons around ejected planets would be direct fossils of the dynamical ejection process and could be tidally heated, potentially habitable worlds. The same simulations show the Roman Space Telescope is even more sensitive, especially toward fainter M-dwarf sources, and that an earlier Roman study overstated its efficiency by fixing single-lens parameters during fitting.","feed_headline":"CSST can detect exomoons around free-floating planets","feed_subtitle":"Moon-mass satellites around Neptune-size drifters would become visible in the planned bulge survey.","key_machinery":"The load-bearing element is the detection-efficiency map in the $(s,q)$ plane. Mock planet-satellite (2L1S) light curves are generated with the VBBinaryLensing code, then fitted to single-lens finite-source models using MCMC and map-making; a satellite counts as detected when the best-fit $\\Delta\\chi^2$ exceeds 100, and efficiency is the fraction of source-trajectory angles $\\alpha$ meeting that threshold. The caustic structures doing the work are the central caustic, which produces the $s\\leftrightarrow1/s$ degenerate sensitivity pattern, and the satellite caustics, whose perturbations dominate at wide separations; finite-source effects and event timescales control how much of the signal survives.","core_discovery":"Simulating 2L1S microlensing events with a satellite companion and fitting them with single-lens models, the paper computes detection efficiency as a function of mass ratio $q$ and projected separation $s$ (in Einstein radii) for CSST and Roman. For a G2V source and a disk Neptune-class lens, CSST's 50% efficiency zone reaches $q\\sim10^{-3}$ (Moon mass) at $s\\approx1$ and spans roughly a decade in separation for $q\\sim10^{-2}$ (Earth mass), with the close-wide degeneracy making the efficiency pattern symmetric around $s=1$. Sensitivity degrades substantially for Earth-mass lenses, for bulge lenses, and for M0V sources; Roman retains much of its sensitivity for M-dwarf sources because it observes in the infrared. The paper also finds that previously published Roman sensitivity estimates were inflated because the single-lens model parameters were held fixed to the true values rather than freely fitted.","pith_inferences":["If the predicted yields are realized, mass-ratio and separation distributions of FFP exomoons would become a new observable for testing planet-planet scattering models, complementing the FFP mass function itself.","The same simulation pipeline could be turned on bound planets on wide orbits or on 1L2S events, since the paper explicitly defers the binary-source degeneracy.","A null detection in the first few years of Roman's survey would bound the exomoon survival fraction and could be published as a meaningful upper limit, not just a failed search.","The close-wide degeneracy means individual detections will be ambiguous in separation; stacking many events may break the degeneracy statistically."],"forward_implications":["CSST should be able to discover Earth-mass exomoons around Neptune-class free-floating planets across projected separations from about 0.01 to 0.1 AU.","Moon-mass satellites ($q\\sim10^{-3}$) become detectable near $s\\approx1$, plus a narrower Moon-mass window around $s\\approx2$ for Earth-mass hosts.","M-dwarf sources sharply reduce CSST's reach, but Roman's infrared survey should still detect Moon-mass satellites and even sub-Moon-mass ones at wide separations.","Detected exomoon populations would directly probe whether satellites survive planetary ejection and at what orbital radii.","Some detectable Neptune-Earth systems should be tidally heated, making them interesting habitability targets."],"supporting_citations":[{"why":"Supplies the CSST survey simulation conventions (cadence, filter, noise floor) and the source/lens parameter sets.","marker":"Yan & Zhu (2022)"},{"why":"Provides the Roman Galactic Bulge Time Domain Survey design and W149 photometric performance used in the Roman simulations.","marker":"Penny et al. (2019)"},{"why":"The prior Roman exomoon sensitivity study whose efficiency estimates this paper re-derives and finds inflated.","marker":"Sajadian & Sangtarash (2023)"},{"why":"Provides the VBBinaryLensing code used to generate the mock planet-satellite light curves.","marker":"Bozza et al. (2018)"},{"why":"Establishes the detection-efficiency methodology, the map-making algorithm for finite-source models, and the warning against fixing single-lens parameters.","marker":"Dong et al. (2006)"},{"why":"Introduced the fraction-of-trajectories definition of detection efficiency that the paper follows.","marker":"Rhie et al. (2000)"},{"why":"Identifies central-caustic perturbations and the close-wide symmetry that shapes the efficiency maps.","marker":"Griest & Safizadeh (1998)"},{"why":"Shows ejected planet-satellite systems can be tidally heated, motivating the tidal-heating discussion for Neptune-Earth systems.","marker":"Debes & Sigurdsson (2007)"}],"fun_headline_variants":["CSST could spot Moon-mass moons around free-floating planets","Exomoon detection around drifters: CSST vs Roman microlensing","Roman's exomoon sensitivity better than previously claimed","Moon-mass exomoons detectable around Neptune-sized FFPs","CSST and Roman can find moons of ejected planets"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The sensitivity numbers assume the idealized CSST observing pattern adopted in Section 2: 60-second i-band exposures, a 0.001 magnitude systematic noise floor, 40% duty cycle, and 8 exposures per 1.5-hour orbit, so if the real survey uses a different cadence, filter, or noise floor, the quoted mass-ratio and separation limits will move.","fun_headline_variants_meta":{"raw":{"variants":["CSST could spot Moon-mass moons around free-floating planets","Exomoon detection around drifters: CSST vs Roman microlensing","Roman's exomoon sensitivity better than previously claimed","Moon-mass exomoons detectable around Neptune-sized FFPs","CSST and Roman can find moons of ejected planets"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000602,"raw_usage":{"total_tokens":2847,"prompt_tokens":1019,"completion_tokens":1828,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":635,"completion_tokens_details":{"reasoning_tokens":1744}},"tokens_in":635,"tokens_out":1828,"duration_ms":13193,"temperature":1.0,"reasoning_tokens":1744,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T21:41:48.746922+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Take the first season of actual CSST bulge data and search short FSPL events for caustic anomalies; if the observed number of Neptune-class FFP events matches current rate estimates but no Moon-mass satellite perturbation appears near the Einstein radius, the predicted detection efficiency is too high. The comparison is also directly testable by re-running the Sajadian & Sangtarash (2023) simulations with free single-lens parameters, which should lower their reported efficiencies toward the values reported here.","supporting_citations":[{"cited_title":"2022, Research in Astronomy and Astrophysics, 22, 025006","cited_arxiv_id":null,"evidence_quote":"Supplies the CSST survey simulation conventions (cadence, filter, noise floor) and the source/lens parameter sets."},{"cited_title":"2023, MNRAS, 520, 5613","cited_arxiv_id":null,"evidence_quote":"The prior Roman exomoon sensitivity study whose efficiency estimates this paper re-derives and finds inflated."},{"cited_title":"2018, MNRAS, 479, 5157","cited_arxiv_id":null,"evidence_quote":"Provides the VBBinaryLensing code used to generate the mock planet-satellite light curves."},{"cited_title":"H., Bennett, D","cited_arxiv_id":null,"evidence_quote":"Introduced the fraction-of-trajectories definition of detection efficiency that the paper follows."},{"cited_title":"1998, ApJ, 500, 37","cited_arxiv_id":null,"evidence_quote":"Identifies central-caustic perturbations and the close-wide symmetry that shapes the efficiency maps."},{"cited_title":"H., & Sigurdsson, S","cited_arxiv_id":null,"evidence_quote":"Shows ejected planet-satellite systems can be tidally heated, motivating the tidal-heating discussion for Neptune-Earth systems."}],"review_version":1}