{"id":"18c2099d-0c03-4733-92d0-d54fdd479f47","arxiv_id":"2501.17241","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":9,"one_line_summary":"The observed edges of the short-period rocky planet population can be explained by photoevaporation, stellar tides, and magnetic drag on planets orbiting inside the stellar magnetic field.","lead":"This paper finds that the maximum mass of short-period rocky planets is set by a combination of photoevaporation and tidal decay, while a deficit of tiny planets inside one-day orbits is caused by magnetic drag from the host star. It offers a single physical explanation for several observed edges in the exoplanet population and predicts where future surveys should find, or not find, small planets.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Concern: the tidal edge hinges on a hot-Jupiter Q'_star(P) extrapolation to untested periods and masses, and the paper concedes a constant Q' can fit the data within age scatter; a statistical model comparison is needed before the edge can be called a physical destruction boundary.","rationale":"Agree with the reader's weakest assumption. The Q' extrapolation is load-bearing because the entire tidal component of the central claim—that observed edges are physical destruction boundaries—depends on it. The paper gives some reasons for optimism: Q'_star is a stellar quantity and Mp/Mstar≪1 in both populations, and the simulations consistently reproduce the analytic edge. But those are not independent tests of Eq. (15): the simulations adopt it as an input, and the analytic comparison to data is visual. The paper's own caveat in §2.1.2—that a constant Q' with realistic age scatter can also provide an adequate fit—is the key admission: if the data cannot reject constant Q', then the period-dependent shape of the edge is not actually constrained by the observations. A conditional verdict is therefore appropriate: the central idea is coherent and physically motivated, but the empirical support for the specific tidal boundary is weaker than the text implies. The magnetic drag boundary has a similar parameter-uncertainty problem (B_star_i, wind mass-loss rate and velocity), but it concerns a separate prediction (the sub-Earth desert) and is not what gives the 10 M⊕ edge its claimed physical origin. The proposed Bayesian comparison would settle whether the Q' extrapolation lands; if it does not, the central claim should be weakened from 'demonstrated' to 'proposed.'","tokens_in":24806,"tokens_out":6062,"duration_ms":60259,"concrete_test":"Perform a hierarchical Bayesian fit to the same mass-period sample used in Figure 1, with a forward model of the upper envelope that includes the RV/TTV selection function and host-star age and radius priors. Compare three models: no tidal edge, a constant Q'_⋆=10^7 edge (Eq. 13), and the period-dependent Q'_⋆ edge (Eqs. 15–16), and in a fourth model allow the normalization and period index of Q'_⋆ to be free. If the period-dependent model does not beat the constant-Q' model by Δln Z > 2.3, or the free-index model does not prefer an index near −3.1 with tight posteriors, then the current data do not establish that a period-dependent hot-Jupiter-style Q' carves the mass-period edge.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The most load-bearing step is the tidal boundary used to explain why the maximum rocky-planet mass declines only mildly inside P≈1 day. Eq. (16), Mp,tide ≈ 10.8 M⊕ (Q'_⋆,0/10^6)(M⋆/M☉)^{-7/3}(P/1 d)^{1.23}, is not an independent physical prediction: it follows from inserting Eq. (15), Q'_⋆ = 10^6(P/2 d)^{-3.1}, into Eq. (13). Eq. (15) is a fit to hot Jupiters; the rocky planets used to define the observed edge are at shorter periods and lower masses, and the stellar mass range extends to 0.09–1.42 M☉. If Q'_⋆ has a different normalization or a different period index, Eq. (16) changes by a large factor and the predicted edge can become a steep cliff (constant Q' gives Mp,tide ∝ P^{13/3}). The paper explicitly acknowledges in §2.1.2 that a constant Q' may also fit the current data within the age scatter, and in §4.2 that the stellar-type dependence of Q' is uncertain. Because the comparison to data in Figure 1 is visual, not a statistical fit, the data shown do not yet discriminate between the period-dependent tidal model and alternative explanations, including selection effects or a different Q'. The simulations in §3 use Eq. (15) as an input, so they corroborate the analytic edge but do not test this extrapolation.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"Lee and Owen present an analytic and numerical study of the short-period rocky planet population, arguing that the observed edge near ~10 Earth masses in mass-period space and the deficit of sub-Earth planets inside ~1 day are produced by three physical processes: photoevaporation, stellar tidal decay, and magnetic drag. They derive (Eq. 6) the maximum core mass that can be stripped by photoevaporation (~15 Earth masses, weakly dependent on period), (Eq. 16) the maximum mass that survives tidal decay when the stellar tidal quality factor is taken from the hot-Jupiter fit Q'_star = 10^6 (P/2d)^-3.1, and (Eq. 32) a minimum survival radius against magnetic drag for a time-dependent dipole field. They compare these boundaries by eye to NASA Exoplanet Archive data in Figures 1 and 2, and show in Section 3 that numerical evolution of a synthetic population with photoevaporation, tides, and magnetic drag reproduces the analytic edges. The paper closes by discussing implications for disintegrating planets and by listing caveats on XUV evolution, Q'_star stellar-type dependence, and magnetic field/wind assumptions.","tokens_in":25158,"tokens_out":6205,"duration_ms":61627,"significance":"If correct, the paper provides a coherent physical explanation for demographic edges that have sometimes been attributed to observational artifacts or to formation limits. The analytic derivations are internally consistent, the simulations use updated tabulated photoevaporation efficiencies, and the resulting scalings (e.g., M_p,tide ∝ P^1.23 and R_p,mag ∝ P^-1.34) are falsifiable with future mass and radius measurements around M and A stars. The authors are transparent about their assumptions and propose concrete observational tests, which strengthens the paper. However, because the data comparison is visual and the tidal boundary relies on an empirical hot-Jupiter relation, the strength of the central demographic claim is currently limited and needs a quantitative comparison to alternatives.","major_comments":[{"comment":"The tidal edge is not an independent prediction: Eq. (16) is obtained by substituting Eq. (15), an empirical fit to hot Jupiters, into Eq. (13). The paper itself concedes (Sec. 2.1.2, p. 5) that a constant Q'_star can also fit the current data within the age scatter, and Sec. 4.2 notes that the stellar-type dependence of Q'_star is uncertain. Because the comparison in Figure 1 is by eye, the data do not discriminate between the period-dependent model and a constant-Q' model. I request a quantitative comparison: for example, compute the likelihood of the observed maximum mass as a function of period under both Q' prescriptions with the same age distribution, or fit Q'_star(P) directly to the rocky-planet sample. Without such a test, the mild mass decline inside ~1 day cannot be uniquely attributed to tides over a constant-Q' scenario that would predict a much steeper P^{13/3} cliff.","section":"Sec. 2.1.2, Eqs. (15)-(16)"},{"comment":"The simulations adopt Eq. (15) as an input when the orbital evolution is solved with dynamic tides (text preceding Fig. 3 refers to equations 12 and 15). They therefore verify internal consistency between the analytic and numerical treatments, but they cannot validate the extrapolation of the hot-Jupiter Q'_star relation to the rocky-planet regime. To test the hypothesis, the simulations should be rerun with a constant Q'_star, or with Q'_star varying with stellar type, and the resulting edges compared to the data. The statement that the simulations produce 'demographic features similar to the observed population' is currently a consistency check, not independent confirmation.","section":"Sec. 3, Fig. 3"},{"comment":"The magnetic drag boundary depends sensitively on adopted values of B_star,i = 100 G, Mdot_w = 10^-12 M_sun/yr, v_w = 100 km/s, a dipolar field, and B_star ∝ t^-0.6; none of these are fit to the target population. The agreement in Figure 2 is qualitative, and the three outlier planets (TOI-6255 b, KOI-4777.01, GJ 367 b) are discussed individually through slow-rotation and low-stellar-mass arguments, but no statistical test is presented. Since the sub-Earth desert is a small-number feature, the paper as written does not yet demonstrate that magnetic drag carves the observed desert. I recommend quantifying the expected number of sub-Earth ultra-short-period planets under the magnetic-drag model, convolving over stellar mass, age, and magnetic field distributions, and comparing with occurrence rates including completeness corrections.","section":"Sec. 2.2.1, Eqs. (29)-(32), Fig. 2"}],"minor_comments":[{"comment":"The caption says 'evaporation time spanning 9-14, 4-14, 2-14, and 2-7 Gyr'; this presumably means the system age used for the boundaries, not an evaporation timescale, and the wording should be clarified.","section":"Fig. 1 caption"},{"comment":"There is a typo: 'evpaoration' should be 'evaporation'.","section":"Sec. 4, Fig. 4 caption"},{"comment":"The symbol P is used for both the dissipated power and the orbital period; renaming the power (e.g., dot{E}) would avoid confusion.","section":"Sec. 2.2.1, Eq. (18)"},{"comment":"The main text states the sub-Earth desert is 'unlikely to be a detection bias', while footnote 1 concedes that ultra-short-period planets can be hard to detect due to finite Kepler cadence; these statements should be reconciled or the bias quantified.","section":"Sec. 2.2, p. 2"},{"comment":"The phrase 'remarkable agreement' is used although the comparisons are visual; given the acknowledged parameter uncertainties, a more quantitative phrasing such as 'consistent with the data within the assumed parameter ranges' would be more appropriate.","section":"Sec. 4 throughout"}],"recommendation":"major_revision","confidential_remarks":"This is a stimulating and useful theory paper with an unusually clear presentation of the physical picture. My main concern is that the central demographic claim--that tides and magnetic drag carve the observed edges--is supported by visual comparison and by simulations that adopt the contested tidal relation as an input. A quantitative model comparison (constant Q' vs. period-dependent Q', and a predicted occurrence rate for the sub-Earth desert) would put the claim on much firmer ground. I see no concerns about novelty or citation practice; the paper fits the journal's scope well."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The thing to know about this paper is that it is a genuinely synthetic theory paper, not another population fit. Lee and Owen take three observed edges in the short-period rocky planet population — the ~10 Earth mass ceiling, the mild decline inside ~1 day, and the sub-Earth desert — and attribute them to photoevaporation, stellar tides, and magnetic drag respectively. The magnetic drag attribution is the new content, and it is worth taking seriously: the paper shows that for sub-Earths the magnetic torque scales as R_p^2 while tidal torque scales as R_p^8, so the switch from tide-dominated to magnetic-drag-dominated orbital decay for the smallest planets is physically sensible. The derivation of the drag boundary is internally consistent, and the sub-Alfvénic check is a nice self-consistency argument.\n\nWhat the paper does well is that the predicted edges are not fit to the target population. Inputs like L_XUV, t_sat, Q'_star, wind mass loss, and B_star are taken from independent measurements, and the analytic equations are transparent enough to check. Equation (6) recovers the expected photoevaporation mass scale, and the simulations in Section 3 reproduce the analytic edges. The scenario for disintegrating planets — that they start near ~1 day with masses 0.1–0.3 Earth masses and spiral in under magnetic drag — is new and gives a concrete, falsifiable population prediction.\n\nThe soft spots are concentrated in the tidal edge, and the stress-test note lands there. Equation (16) is not an independent prediction; it follows directly from plugging the hot-Jupiter Q'_star(P) relation of Penev et al. (2018) into the standard tidal decay timescale. If Q' is constant instead, the predicted edge becomes a steep cliff, and the paper itself concedes in Section 2.1.2 that a constant Q' can fit the data within the age scatter. So the current visual comparison does not discriminate between these models. The extrapolation to 0.09–1.42 solar mass stars is acknowledged but not tested. The magnetic drag boundary depends on uncertain B_star, wind, and conductivity parameters, and the three outlier planets are explained away by slow rotation rather than independently confirmed. The sample behind the mass-period edge is small and completeness-limited, and the comparisons are visual, not statistical. None of this is fatal, but it means the central claim is a strong hypothesis, not a demonstrated destruction boundary.\n\nThis paper deserves a serious referee. The theory is clear, the caveats are honestly stated, and the magnetic drag mechanism for sub-Earths is novel enough to warrant careful scrutiny. I would send it to review, asking for a statistical comparison of the period-dependent and constant Q' models and a sensitivity analysis on the magnetic drag parameters. It belongs in the reading group and I would cite it when discussing ultra-short-period planet occurrence.","headline":"A coherent, parameter-light theory for the three edges in short-period rocky planets, with magnetic drag as the genuinely new piece, but the tidal edge rests on an extrapolated Q'(P) and the data comparison is visual, so it is strongly suggestive rather than proven.","tokens_in":25775,"tokens_out":2130,"would_cite":true,"duration_ms":23731,"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":"Photoevaporation, tidal decay, and magnetic drag carve the observed edges of the short-period rocky planet population.","keywords":["rocky planets","ultra-short-period planets","photoevaporation","tidal decay","magnetic drag","radius-period space","stellar magnetic field","planet occurrence edges"],"falsifier":"Measure the rotation period and surface magnetic field of the host star of GJ 367 b (0.32-day period, 0.7 Earth radii): the magnetic drag model requires that this star be a slow rotator with a weak large-scale field, otherwise the planet's survival would contradict Equation (32); likewise, a single rocky planet above the mass-period curve of Equation (16) would falsify the tidal edge.","tokens_in":24508,"feed_emoji":"🪐","tokens_out":9296,"duration_ms":78609,"temperature":0.7,"pith_summary":"This paper argues that the sharp edges seen in the short-period rocky planet population are not observational artifacts but physical destruction boundaries. Over 0.2–20 day orbits around stars of 0.09–1.42 solar masses, no rocky planet exceeds about 10 Earth masses, and there is a deficit of sub-Earth-sized planets inside about one day. The authors show analytically and with numerical simulations that photoevaporation sets which cores lose their gas envelopes, stellar tides remove the more massive cores at the shortest periods, and magnetic drag from the star's field sweeps away sub-Earth planets inside about a day. If correct, the observed edges directly trace the strengths of star-planet interactions and can be used to calibrate them.","feed_headline":"Three forces carve the edges of rocky planets","feed_subtitle":"The 10-Earth-mass cap and the sub-Earth desert are destruction boundaries, not survey artifacts.","key_machinery":"The argument is carried by three analytic scaling relations, each tied to one physical mechanism: the energy-limited photoevaporation mass-loss formula with an efficiency $\\eta \\sim 0.1 (M_p/10 M_\\oplus)^{-1}$; the tidal decay timescale with a period-dependent stellar tidal quality factor $Q'_\\star = 10^6 (P/2\\,\\mathrm{days})^{-3.1}$, which yields the maximum surviving mass in Equation (16); and the magnetic drag power from a closed star–planet circuit with a dipolar stellar field decaying as $t^{-0.6}$, which yields the minimum surviving radius in Equation (32). These relations define the allowable region of mass–period and radius–period space for surviving rocky planets, and the paper verifies them with numerical simulations that evolve planet interiors and orbits together.","core_discovery":"The central claim is that the upper edge of the rocky planet mass-period distribution, near 10 Earth masses, and the inner edge of the sub-Earth radius-period distribution, around 1 Earth radius inside roughly one day, are carved by three distinct physical mechanisms. Photoevaporation by stellar XUV radiation strips the gaseous envelopes of cores up to about 15 Earth masses, with a weak period dependence. Tidal decay, using a period-dependent stellar tidal quality factor $Q'_\\star = 10^6 (P/2\\,\\mathrm{days})^{-3.1}$ inferred from hot Jupiters, imposes a maximum surviving mass that drops steeply at periods below about 1.34 days. Magnetic drag, the closed-circuit Joule dissipation of the planet's orbital motion through the stellar field, imposes a minimum surviving radius $R_{p,\\mathrm{mag}} \\sim 0.6 R_\\oplus (P_p/1\\,\\mathrm{day})^{-1.34}$. Numerical simulations that co-evolve planetary interiors and orbits with all three processes reproduce the observed edges, showing the demographic limits are physical destruction boundaries.","pith_inferences":["A completeness-corrected occurrence-rate survey of ultra-short-period planets would test the magnetic drag boundary more sharply than the current sparse sample, since the model predicts a sharp downturn in occurrence toward small radii inside one day.","The magnetic drag model implies that the survival of the three known sub-Earth ultra-short-period planets (TOI-6255 b, KOI-4777.01, GJ 367 b) requires their host stars to be slow rotators with weak large-scale fields; measuring their spin periods would directly test the model.","The same combination of mechanisms, applied to higher-mass planets, may unify the sub-Jovian desert and radius cliff with the rocky planet edges; the paper sketches this connection, but a population synthesis with realistic initial conditions would be needed to show one model spans all the demographic boundaries.","Around mid-late M dwarfs, stronger magnetic fields and potentially lower tidal quality factors would shift both destruction boundaries inward in period, predicting that ultra-short-period rocky planets are even rarer around fully convective stars; future surveys over a wide stellar-mass range can test this."],"forward_implications":["If the paper is right, the ~10 Earth-mass cap on rocky planet masses marks the point where tidal decay destroys the planet, not the critical core mass for runaway gas accretion.","The sub-Earth desert inside about one day is a destruction signature of magnetic drag, meaning the missing planets were removed by star-planet magnetic interaction rather than never formed or missed by surveys.","The predicted mass-period and radius-period edges provide a demographic probe of stellar tidal quality factors and magnetic field strengths, including their dependence on stellar mass and age.","Catastrophically evaporating planets such as Kepler-1520 b are interpreted as planets of roughly 0.1–0.3 Earth masses that began their inward spiral near one day under magnetic drag and were destroyed by Joule heating before reaching the Roche limit.","Around fully convective stars below 0.35 solar masses, the same physics predicts a lower maximum rocky planet mass, consistent with the observed ~4 Earth-mass maximum, linking destruction edges to the formation-limited core mass distribution."],"supporting_citations":[{"why":"Identifies the observed ~10 Earth-mass upper limit of rocky planets over 0.2–30 days that the paper sets out to explain.","marker":"Parc et al. (2024)"},{"why":"Supplies the photoevaporation mass-loss model and the simplified efficiency relation (their equation 31) used to derive the maximum stripped core mass.","marker":"Owen & Wu (2017)"},{"why":"Provides the empirically fitted period-dependent stellar tidal quality factor $Q'_\\star = 10^6 (P/2\\,\\mathrm{days})^{-3.1}$ that converts tidal decay into a weak mass-period edge.","marker":"Penev et al. (2018)"},{"why":"Gives the magnetic drag power formula and the planet-to-star resistance ratio used to compute Joule heating and orbital decay.","marker":"Laine & Lin (2012)"},{"why":"Provides the star-planet magnetic circuit framework and twist criterion; the paper shows its sub-Alfvénic condition keeps the circuit closed.","marker":"Lai (2012)"},{"why":"Reports the observed deficit of sub-Earth planets inside a few days that the magnetic drag boundary must reproduce.","marker":"Dattilo et al. (2023)"},{"why":"Supplies the measured time decline of stellar magnetic field strength ($B \\propto t^{-0.655}$) used to evolve the magnetic drag with age.","marker":"Vidotto et al. (2014)"},{"why":"Gives the Roche-lobe radius coefficient ($q = 2.44$) used as the destruction limit for tidal and magnetic inspiral.","marker":"Rappaport et al. (2013)"},{"why":"Provides the fiducial stellar wind mass-loss rate and speed used in the magnetic drag calculation.","marker":"Johnstone et al. (2015a)"}],"fun_headline_variants":["Three forces carve rocky planet edges","Rocky planet edges are physical destruction zones","Photoevaporation, tides, and magnetic drag shape planets","The 10-Earth-mass cap and sub-Earth desert explained","Stellar light, tides, and magnetism set planet limits"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The whole prediction hinges on assuming that the tidal dissipation strength measured for hot Jupiters and the assumed magnetic field of the star also hold for rocky planets around very different stars, so a change in either would move the predicted edges.","fun_headline_variants_meta":{"raw":{"variants":["Three forces carve rocky planet edges","Rocky planet edges are physical destruction zones","Photoevaporation, tides, and magnetic drag shape planets","The 10-Earth-mass cap and sub-Earth desert explained","Stellar light, tides, and magnetism set planet limits"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001137,"raw_usage":{"total_tokens":4770,"prompt_tokens":1044,"completion_tokens":3726,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":660,"completion_tokens_details":{"reasoning_tokens":3650}},"tokens_in":660,"tokens_out":3726,"duration_ms":26207,"temperature":1.0,"reasoning_tokens":3650,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T04:44:50.107048+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the rotation period and surface magnetic field of the host star of GJ 367 b (0.32-day period, 0.7 Earth radii): the magnetic drag model requires that this star be a slow rotator with a weak large-scale field, otherwise the planet's survival would contradict Equation (32); likewise, a single rocky planet above the mass-period curve of Equation (16) would falsify the tidal edge.","supporting_citations":[],"review_version":1}