{"id":"a389bfe6-afc6-42ff-af46-4c62d445bb3e","arxiv_id":"2608.03435","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Across Chandrayaan-2/3, Venus Express, and Akatsuki data, interplanetary plasma adds mHz-level Doppler noise to S-band signals and smaller X-band noise, while lunar ionosphere and coronal paths show much larger fluctuations.","lead":"Radio signals from five spacecraft missions show small Doppler frequency wobbles caused by electrons in interplanetary space, measured outside the Moon's atmosphere and away from the Sun. The numbers give baselines for plasma noise in S-band and X-band tracking, useful for future deep-space navigation and radio occultation science.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Detrended one-way residuals are not shown to be dispersive; without S/X ratio or calibration the IPM attribution is unverified.","rationale":"The paper's qualitative ordering—quiet IPM paths show smaller fluctuations than lunar or coronal paths, and S-band is more affected than X-band—is physically plausible and consistent with established radio-propagation results. The CH3PM IPM-only dataset is a genuinely new contribution. However, the quantitative claim that these residuals 'quantify the IPM contribution to Doppler noise' requires demonstrating that the detrended residual floor is not dominated by non-dispersive measurement or dynamical systematics. The one-way VeRa pass is the most vulnerable data point because a very large trend is removed and no dual-frequency validation is offered. This is not a claim of misconduct; it is the standard dispersive/non-dispersive separation used in radio science. The reader's weakest assumption—that residuals are dominated by IPM rather than spacecraft dynamics, thermal noise, or ground-station systematics—is precisely the point, and the proposed S/X ratio test gives a concrete way to settle it. Because the test has not been performed and the paper itself acknowledges the limited statistical basis in its final paragraph, the CONDITIONAL verdict remains appropriate: the central claim should be accepted only if such validation is provided. A secondary issue, the inconsistent description of the CH2 spectral slope (α=2.18 reported in Table 1 and Section 3.5 as steep non-Kolmogorov, while the abstract and parts of Section 3.5 call it Kolmogorov-like), should also be corrected, but it is not the primary load-bearing concern.","tokens_in":16106,"tokens_out":7078,"duration_ms":70292,"concrete_test":"For the VeRa 15 Dec 2008 pass, obtain simultaneous S-band and X-band open-loop residuals processed through the same f_th model. Band-pass both time series over 1–100 mHz and compute (a) the ratio of RMS fluctuation amplitudes and (b) the cross-correlation coefficient between the two residual series. If the IPM dominates, the RMS ratio should be close to f_X/f_S ≈ 3.6 and the residuals should be strongly correlated. If the ratio is near 1, or the correlation is low, non-dispersive systematics dominate and the IPM attribution fails. If simultaneous S/X data are not available for that pass, repeat the same test on any dual-frequency one-way IPM-only pass (e.g., VeRa or Akatsuki with ground-truth calibration) or apply the same analysis to a calibration pass through a known non-plasma geometry.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim rests on Equation (1): the residuals Δf(t)=f_obs−f_th are interpreted as cumulative plasma refractive effects, and after detrending in Sections 3.1–3.3 the remaining fluctuations are attributed to the IPM. The load-bearing, untested assumption is that these residuals are dispersive (plasma-dominated) rather than non-dispersive (spacecraft dynamics, oscillator/station reference, or ground systematics). This is most acute for the one-way VeRa S-band pass: the raw residual drifts by roughly 1000 Hz over 90 minutes, a spline removes that trend, and the remaining ±2.5 Hz residual is attributed to IPM. A constant or slowly varying frequency offset from the oscillator, ground reference, or predicted-frequency model would produce exactly this pattern. For plasma-induced Doppler fluctuations, the amplitude scales as 1/f, so simultaneous S-band and X-band downlinks should show amplitude ratio f_X/f_S ≈ 3.6 and high correlation; for non-dispersive systematics, the Hz-level residuals would be common-mode and uncorrelated with frequency. The paper does not perform this discriminating test and reports no Allan-deviation or independent calibration pass. For CH3PM, unmodeled non-gravitational accelerations in the highly elliptical orbit could similarly leave mHz-level residuals after polynomial detrending, so the mHz floor is not uniquely attributable to IPM without additional dynamic or dispersive validation.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper analyzes Doppler residuals from five radio occultation datasets: two-way S-band from the Chandrayaan-3 propulsion module (CH3PM) outside the lunar ionosphere, two-way S-band from Chandrayaan-2 (CH2) in lunar occultation, one-way S-band from Venus Express (VeRa) in IPM-only geometry, one-way X-band from Akatsuki in IPM-only geometry, and one-way X-band from Akatsuki in solar occultation. The authors compute residuals Δf = f_obs − f_th using a relativistic light-time model, detrend them with polynomials or splines, and attribute the detrended fluctuations to the interplanetary medium (IPM). They report mHz-level fluctuations for IPM-only datasets, larger fluctuations for CH2 and solar occultation, and power spectral density spectral indices ranging from −0.68 to 2.18. The central claim is that these results quantify the IPM contribution to Doppler noise and demonstrate the enhanced plasma sensitivity of two-way coherent S-band links.","tokens_in":16438,"tokens_out":9190,"duration_ms":74376,"significance":"If the attribution of the detrended residuals to IPM is valid, the paper provides useful multi-frequency empirical constraints on IPM turbulence far from the Sun and a benchmark for plasma-induced noise in spacecraft tracking and radio science. The study covers a useful spread of frequencies, link configurations, and geometries, and the CH3PM two-way S-band detection of mHz-level fluctuations is a potentially interesting result. However, the quantitative claims currently rest on an untested assumption that the residuals are plasma-dominated; the paper does not provide a dispersive discriminator, and the spectral analysis contains internal inconsistencies and no uncertainties. The significance of the paper depends on resolving these issues.","major_comments":[{"comment":"The manuscript contains a direct contradiction about the CH2 spectral index. In Section 3.5 it states that CH2 has α ~ 2.18, 'which implies steep, non-Kolmogorov, dissipative turbulence,' and later in the same section that 'The CH2 S-band and Akatsuki X-band solar occultation datasets exhibit clear power-law behavior over a broad frequency range, with slopes consistent with Kolmogorov turbulence.' The abstract's claim of Kolmogorov-like turbulence for the lunar occultation case is inconsistent with the reported α = 2.18. Please correct this discrepancy and specify the expected Kolmogorov value (α = 2/3).","section":"Section 3.5, Table 1, Abstract"},{"comment":"The central attribution of the detrended Doppler residuals to IPM is not validated. Equation (1) defines Δf(t) as the cumulative refractive effect of plasma, but this is an interpretive assumption: the residual also contains any unmodeled dynamics, oscillator noise, ground-station systematics, and media other than the IPM. The paper does not perform a dispersive test (for plasma, simultaneous S/X amplitude ratio near f_X/f_S and high correlation; for non-dispersive systematics, ratio near unity), nor does it report an Allan-deviation or calibration pass. For the one-way VeRa S-band pass, where the raw drift is about 1000 Hz over 90 minutes and a spline removes it, the remaining ±2.5 Hz could equally be produced by a slow frequency offset or unmodeled spacecraft motion. For CH3PM, unmodeled non-gravitational accelerations in a highly elliptical orbit could leave mHz-level residuals after polynomial detrending. Unless a dispersive check is provided or the claims are explicitly downgraded to upper limits or interpretation, the abstract's 'quantify' statement is not supported.","section":"Section 2.1, Eq. (1), Sections 3.1–3.3"},{"comment":"The spectral slopes are reported without uncertainties and without a sensitivity analysis. The detrending order/type (second-order polynomial for CH3PM, spline for VeRa) is chosen per dataset and can suppress genuine low-frequency signal or introduce spurious spectral slopes. The fit range [1/N, f_N/10] is stated, but no fitting method or confidence intervals are given. The interpretation of negative α as 'no discernible information' is then contradicted by the later claim that the same datasets 'reflect weak interplanetary turbulence.' Please provide slope uncertainties, a detrending-order sensitivity test, and a clear criterion for when a spectral index is physically meaningful.","section":"Section 3.5, Table 1, Figures 5–9"}],"minor_comments":[{"comment":"Aggarwal et al. 2026a and 2026b appear with identical titles and DOIs; please merge or distinguish them.","section":"References"},{"comment":"The phrase 'one-way S/X band measurements from the Venus Express Radio Science (VeRa)/Akatsuki' is ambiguous: Section 2.3 describes VeRa as S-band only. Please clarify that S-band is from VeRa and X-band from Akatsuki.","section":"Abstract"},{"comment":"The statement that all observations correspond to 'quiet solar and geomagnetic conditions, as indicated by the daily averaged Dst values' is at odds with the reported Dst = 50 for CH2 and the description of X-class flares and CMEs during the CH3PM interval in Sections 1 and 2.1. Please reconcile the text with the Table entries.","section":"Table 1 and text"},{"comment":"The white-noise comparison is only qualitative; no statistical test (e.g., confidence bands on the PSD) is used to establish that the observed PSDs are significantly non-flat.","section":"Figure 10, Section 3.4"}],"recommendation":"major_revision","confidential_remarks":"The manuscript relies heavily on self-citations, including two references (Aggarwal et al. 2026a and 2026b) that appear to be identical; the CH2 calibration reference (Tripathi et al. 2025) is a Zenodo record rather than a peer-reviewed paper. An editorial check of the reference list is advisable. The core technical concern I have is the absence of a dispersive validation, which in my view is the difference between a definitive measurement and a plausible interpretation."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"What you should know: this paper gives you a useful multi-mission baseline for IPM-induced Doppler fluctuations, and the Chandrayaan-3 IPM-only S-band dataset is genuinely new. The qualitative story holds up—fluctuations are smaller far from the Sun and Moon, larger in lunar and coronal paths, and S-band shows more effect than X-band. That is consistent with established plasma propagation physics, and the authors are honest in the final paragraph about the limited statistical basis. Credit where it is due: the paper reports previously unpublished Doppler residuals, makes a sensible cross-mission comparison, and the white-noise reference is a good sanity check.\n\nThe soft spots, in proportion to how soft they are. The main one is that the detrended residuals are never shown to be dispersive. Equation (1) defines the residuals as cumulative plasma refractive effects, but after removing a polynomial or spline trend, the remaining fluctuations are attributed to IPM without testing whether they actually scale with frequency. For the VeRa S-band pass, the raw residual drifts by roughly 1000 Hz over 90 minutes; a spline removes that drift and leaves ±2.5 Hz. An oscillator or ground-reference offset would produce exactly that pattern. For CH3PM, unmodeled non-gravitational accelerations in a highly elliptical orbit could leave mHz-level residuals after detrending. A simple S-band/X-band ratio test or any dispersive check would have strengthened the central claim. I also note the internal inconsistency on the CH2 slope: the abstract says Kolmogorov-like, but Table 1 and Section 3.5 report α = 2.18, which is steep and non-Kolmogorov. That needs to be reconciled. Single observing sessions per geometry mean no error bars on the spectral slopes, so the quantitative comparisons are more illustrative than definitive.\n\nThese are addressable issues, not fatal flaws. The paper is a legitimate empirical contribution that deserves a serious referee. I would send it to peer review with a request for major revision: add a dispersive test (or at least an explicit discussion of the predicted S/X ratio for plasma), report uncertainties on slopes and amplitudes, and fix the slope inconsistency. For someone building a noise budget for deep-space tracking or planning radio occultation experiments, this is a useful anchor, but I would not cite it until the IPM attribution is better supported.","headline":"Useful empirical inventory of IPM-induced Doppler noise across five radio links, but the IPM attribution rests on detrending assumptions and single events.","tokens_in":16902,"tokens_out":1746,"would_cite":false,"duration_ms":16925,"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":"Across five spacecraft datasets, the paper isolates and quantifies the interplanetary medium's contribution to Doppler frequency fluctuations, reporting mHz-level amplitudes that set a plasma-noise floor for precision radio tracking.","keywords":["radio occultation","interplanetary medium","Doppler residuals","plasma turbulence","Chandrayaan-3","Venus Express","Akatsuki","solar wind"],"falsifier":"A definitive check would be a dual-frequency (S-band and X-band) occultation pass along an IPM-only line of sight. Because plasma-induced Doppler shifts scale as $1/f^2$, the S-band and X-band residuals should differ by a factor of roughly $(8.4/2.3)^2\\approx 13.3$ if both are dominated by the same IPM irregularities; non-dispersive errors such as spacecraft dynamics or clock drift would appear equally in both bands and break that ratio. If the observed ratio does not hold, the residuals are not purely interplanetary plasma.","tokens_in":15863,"feed_emoji":"📡","tokens_out":12018,"duration_ms":96806,"temperature":0.7,"pith_summary":"This paper tries to establish that the weak, millihertz-level Doppler fluctuations seen in spacecraft radio signals can be attributed to electron-density irregularities in the interplanetary medium, and that those fluctuations are a measurable plasma-noise floor for radio occultation and precision tracking. It does this by selecting five datasets whose line-of-sight geometries keep the signal away from the Moon, planetary atmospheres, and the solar corona (except for two control cases), then analysing Doppler residuals and their power spectra. The paper reports amplitudes of about ±0.01 Hz for S-band over a roughly 35,000 km Earth–Moon path, about ±2.5 Hz for S-band over a 0.91 AU Earth–Venus path, and about ±0.05 Hz for X-band over a 0.29 AU path. If these numbers are right, future missions can budget for interplanetary plasma as a source of Doppler noise that depends on frequency, link configuration, and propagation geometry.","feed_headline":"mHz wobbles in spacecraft signals trace interplanetary plasma","feed_subtitle":"Five datasets, from Moon-Earth to Venus-Earth paths, pin down the plasma contribution to Doppler noise in radio science.","key_machinery":"The central object is the Doppler residual $\\Delta f(t)=f_{\\mathrm{obs}}(t)-f_{\\mathrm{th}}(t)$, defined in Equation (1) as the cumulative refractive effect of plasma irregularities along the two-way propagation path. After detrending the raw residuals with a low-order polynomial or spline, the paper computes power spectral densities of the detrended time series and compares them with a white-noise baseline; departure from a flat spectrum indicates structured, frequency-dependent plasma fluctuations. The two-way coherent link matters because the signal traverses the same plasma twice, so plasma-induced phase perturbations add while many instrumental noise sources cancel.","core_discovery":"The paper's central claim is that the Doppler residual $\\Delta f(t)=f_{\\mathrm{obs}}(t)-f_{\\mathrm{th}}(t)$ — the difference between the received spacecraft carrier frequency and a prediction from a relativistic light-time model — is, when the line of sight avoids the Moon, planets, and the Sun, a measurement of electron-density irregularities in the interplanetary medium. After detrending, the residuals show fluctuations of about $\\pm 0.01$ Hz for Chandrayaan-3 S-band over an Earth–Moon path of roughly 35,000 km, about $\\pm 2.5$ Hz for Venus Express S-band over a 0.91 AU Earth–Venus path, and about $\\pm 0.05$ Hz for Akatsuki X-band over a 0.29 AU path. The paper argues that these amplitudes are the interplanetary medium's quantitative contribution to Doppler noise, while the larger values from Chandrayaan-2 lunar occultation ($\\pm 0.075$ Hz, spectral index $\\alpha\\approx 2.18$) and Akatsuki solar occultation ($\\pm 2$ Hz, $\\alpha\\approx 0.68$) bracket the non-IPM plasma environments.","pith_inferences":["Inference: A dual-frequency version of the same experiment would test the IPM attribution directly, since a $1/f^2$ plasma signature would force S-band and X-band residuals into a ratio of roughly $(8.4/2.3)^2\\approx 13.3$, while non-dispersive errors would not scale that way.","Inference: Applying the same detrending and spectral pipeline to archival tracking data from other deep-space missions could turn these single-pass case studies into a statistical map of how IPM turbulence strength varies with heliocentric distance, solar cycle, and line-of-sight length.","Inference: Because the Doppler residual is a path-integrated measurement, the technique could be extended beyond noise characterization: with independent electron-density priors, the residuals could be inverted for line-of-sight integrated electron-content fluctuations, offering a remote plasma diagnostic in regions where in-situ spacecraft coverage is sparse."],"forward_implications":["Interplanetary plasma alone produces Doppler fluctuations of about $\\pm 0.01$ Hz at S-band over a ~35,000 km Earth–Moon path, far smaller than the ~$\\pm 0.075$ Hz seen when the same two-way S-band link passes through the lunar ionosphere.","At X-band over a 0.29 AU Earth–Venus path, IPM-only fluctuations are about $\\pm 0.05$ Hz, while the same link at 3.9 solar radii shows $\\pm 2$ Hz, so coronal plasma dominates by roughly two orders of magnitude.","Two-way coherent S-band links are more sensitive to weak IPM fluctuations than one-way X-band links, because the two-way geometry doubles the plasma phase accumulation while cancelling many instrumental noise sources.","Power spectral slopes separate environments: near-lunar and coronal occultation spectra show power-law behavior consistent with an inertial-range cascade, while IPM-only spectra are nearly flat or slightly negative, indicating weak, low-amplitude turbulence far from the Sun and Moon.","The absence of a measurable Doppler-spectrum response to a solar flare in the Chandrayaan-3 data suggests that not every transient solar event produces sufficient plasma along the line of sight to alter the observed fluctuations."],"supporting_citations":[{"why":"Establishes that plasma-induced phase perturbations scale inversely with frequency squared and that two-way coherent links accumulate plasma effects along both paths.","marker":"Woo and Armstrong (1979)"},{"why":"Supplies the Chandrayaan-2 two-way S-band occultation method and the relativistic light-time residual model that the Chandrayaan-3 analysis extends.","marker":"Tripathi et al. (2025)"},{"why":"Describes the Akatsuki radio occultation experiment and the open-loop X-band data acquisition used here.","marker":"Imamura et al. (2011)"},{"why":"Describes the Venus Express Radio Science (VeRa) experiment and S-band data acquisition used for the IPM-only comparison.","marker":"Häusler et al. (2006)"},{"why":"Supplies the convention that maps PSD slope alpha to turbulence index p via alpha = p - 3, with p = 11/3 for Kolmogorov spectra.","marker":"Armand et al. (2003)"},{"why":"Provides prior evidence that spacecraft signals can show IPM phase scintillation away from solar conjunction, the baseline this study quantifies.","marker":"Molera Calvés et al. (2014)"},{"why":"Supplies the second-order polynomial detrending approach applied to the Doppler residuals before spectral analysis.","marker":"Aggarwal et al. (2026a)"}],"fun_headline_variants":["Interplanetary plasma leaves mHz mark on spacecraft signals","Doppler noise from interplanetary medium quantified in five datasets","Chandrayaan and Akatsuki pin down interplanetary plasma in radio signals","mHz-level Doppler wobbles trace interplanetary electron density","Five radio datasets isolate interplanetary medium's Doppler fingerprint"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the detrended Doppler residual is dominated by interplanetary plasma fluctuations rather than by unmodeled spacecraft dynamics, thermal noise, clock drift, or ground-station systematics.","fun_headline_variants_meta":{"raw":{"variants":["Interplanetary plasma leaves mHz mark on spacecraft signals","Doppler noise from interplanetary medium quantified in five datasets","Chandrayaan and Akatsuki pin down interplanetary plasma in radio signals","mHz-level Doppler wobbles trace interplanetary electron density","Five radio datasets isolate interplanetary medium's Doppler fingerprint"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000177,"raw_usage":{"total_tokens":1383,"prompt_tokens":1128,"completion_tokens":255,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":744,"completion_tokens_details":{"reasoning_tokens":167}},"tokens_in":744,"tokens_out":255,"duration_ms":2627,"temperature":1.0,"reasoning_tokens":167,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T14:49:03.872596+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A definitive check would be a dual-frequency (S-band and X-band) occultation pass along an IPM-only line of sight. Because plasma-induced Doppler shifts scale as $1/f^2$, the S-band and X-band residuals should differ by a factor of roughly $(8.4/2.3)^2\\approx 13.3$ if both are dominated by the same IPM irregularities; non-dispersive errors such as spacecraft dynamics or clock drift would appear equally in both bands and break that ratio. If the observed ratio does not hold, the residuals are not purely interplanetary plasma.","supporting_citations":[{"cited_title":", author Choudhary, R.K","cited_arxiv_id":null,"evidence_quote":"Supplies the Chandrayaan-2 two-way S-band occultation method and the relativistic light-time residual model that the Chandrayaan-3 analysis extends."},{"cited_title":", author Toda, T","cited_arxiv_id":null,"evidence_quote":"Describes the Akatsuki radio occultation experiment and the open-loop X-band data acquisition used here."},{"cited_title":", author Efimov, A","cited_arxiv_id":null,"evidence_quote":"Supplies the convention that maps PSD slope alpha to turbulence index p via alpha = p - 3, with p = 11/3 for Kolmogorov spectra."}],"review_version":1}