{"id":"d3249771-217b-4859-bb8e-21cd8d793a65","arxiv_id":"2607.07009","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"unknown","formal_verification":"none","parameter_count":3,"one_line_summary":"Coordinated MAVEN/IUVS and EMM/EMUS observations show the May 2024 ICME produced a planet-wide enhancement of Martian UV dayglow via simultaneous proton and electron precipitation.","lead":"This paper shows that a major solar storm in May 2024 simultaneously intensified three types of ultraviolet light from Mars's upper atmosphere, driven by both proton and electron precipitation. It matters because it demonstrates a planet-wide atmospheric response to space weather using two spacecraft at once, constraining how energy deposits across the thermosphere.","discovery_kind":"unclear","skeptic_critique":{"model":"glm-5.2","headline":"The EMUS quiet-time baseline (20 April) is separated from the event (18 May) by ~4 weeks spanning Ls ~240°→270°, a seasonal transition that independently expands the H corona and alters dayglow emissions, potentially conflating seasonal and ICME-driven enhancements in the disk observations used to e","rationale":"The reader correctly identified the single-scan EMUS baseline as a weakness but framed it as a generic 'sampling bias' issue. The more specific and load-bearing problem is that the ~4-week temporal gap is not random — it spans a known seasonal transition that the paper itself identifies as relevant to hydrogen corona expansion and proton aurora intensity. This is not a generic sampling concern; it is a systematic confound that acts in the same direction as the claimed ICME effect for H Lyman-α. The IUVS limb data (temporally well-controlled) supports the vertical enhancement claim, but the horizontal/planetary-scale claim — the paper's key advance over prior work — rests materially on the EMUS comparison. The reader's secondary concern about the [O(3S)130.4/O(5S)135.6] ratio diagnostic is also valid, but I note that the observed ratio decrease is actually directionally consistent with enhanced electron impact and inconsistent with a pure neutral-density increase (which would tend to increase the ratio by boosting the resonance-scattering-dominated 130.4 nm channel). So the ratio diagnostic is more robust than the reader suggested, while the EMUS baseline issue is more problematic than the reader recognized. The verdict remains CONDITIONAL: the observational result is likely real (IUVS data is strong), but the 'planetary-scale' framing requires the EMUS baseline to be re-checked against a temporally proximate pre-event scan.","tokens_in":15597,"tokens_out":3897,"duration_ms":147809,"concrete_test":"Identify an EMUS disk scan from ~14–16 May 2024 (days immediately before ICME arrival at Mars) with comparable SZA coverage and viewing geometry to the 18 May event scan. Recompute the EMUS enhancement factors (Figure 3c, 3f, 3i and Figure 4) using this pre-event baseline instead of the 20 April scan. If the H Lyman-α enhancement drops below ~50% (from the reported ~80–200%) or the oxygen enhancements become statistically insignificant, seasonal confounding is materially affecting the planetary-scale claim. If enhancements persist at comparable magnitude, the result is robust.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central novelty is the 'near-simultaneous' dual-instrument demonstration of both vertical (IUVS) and horizontal (EMUS) enhancement — i.e., a 'planetary-scale response.' The IUVS comparison is well-controlled: quiet orbits 21212–21218 and event orbits 21219–21227 are consecutive (~hours apart), minimizing seasonal drift. However, the EMUS disk comparison uses a single quiet scan from 20 April 2024 vs. a single event scan from 18 May 2024 — a ~4-week gap during which Mars progressed from Ls ~240° to ~270° (approaching southern summer solstice). The paper itself notes that Ls ~270° is when 'the expanded hydrogen corona favours the most frequent and intense proton aurora events' (Section 4), yet this seasonal effect is invoked only to explain the strength of the ICME response, not to acknowledge that the EMUS baseline may already be biased low for H Lyman-α due to the smaller corona at Ls ~240°. Seasonal variation in thermospheric O/CO2 density ratios could also affect the oxygen emission baselines independently of the ICME. Since the EMUS disk observations are the primary evidence for 'horizontally extensive' and 'planetary-scale' response across latitude, longitude, and local time, a seasonally confounded baseline would weaken the horizontal-extent claim — the component that distinguishes this work from prior single-instrument limb studies. The IUVS vertical enhancement would remain valid, but the 'planetary-scale' framing depends materially on the EMUS comparison being clean.","agreement_with_reader":"partial"},"referee_report":{"model":"glm-5.2","summary":"This manuscript presents near-simultaneous MAVEN/IUVS limb and EMM/EMUS disk observations of Martian UV dayglow emissions (H Lyman-alpha, O(3S) 130.4 nm, O(5S) 135.6 nm) during the May 2024 ICME event. The authors report pronounced enhancements in all three emissions relative to quiet-time conditions, with the response extending vertically through the thermosphere and horizontally across latitude, longitude, local time, and SZA. The concurrent enhancement of hydrogen and oxygen emissions is attributed to simultaneous proton and electron precipitation. The oxygen emission ratio [O(3S)130.4/O(5S)135.6] is used as a diagnostic of photon-driven versus particle-driven excitation. The study is well-motivated, the dual-instrument approach is a genuine strength, and the IUVS limb comparison is well-controlled with consecutive orbits. The manuscript is generally clearly written and the figures support the claims.","tokens_in":16349,"tokens_out":1360,"duration_ms":130239,"significance":"The principal novelty is the coordinated near-simultaneous use of IUVS limb profiles (vertical structure) and EMUS disk images (horizontal extent) to characterize the ICME response in both dimensions, which has not been previously demonstrated. The observational approach of matching quiet-time and event-time orbits for SZA and spatial coverage is sound. The check that solar EUV flux did not increase during the event (Figure S7) addresses an important confound. The use of the oxygen emission ratio as a diagnostic of electron-impact excitation, grounded in prior modeling work (Ritter et al., 2019; Soret et al., 2024), provides a physically grounded attribution framework. These are substantive contributions to the characterization of Martian upper atmospheric response to extreme space weather events.","major_comments":[{"comment":"Section 2 (Data and Methodology) and Section 4 (Discussion): The EMUS disk comparison uses a single quiet-time scan from 20 April 2024 (Ls ~240 deg) versus a single event scan from 18 May 2024 (Ls ~270 deg), a ~4-week seasonal gap. The authors themselves note in Section 4 that Ls ~270 deg is when 'the expanded hydrogen corona favours the most frequent and intense proton aurora events.' This seasonal effect is invoked to explain the strength of the ICME response, but it is not acknowledged as a potential confound for the EMUS baseline comparison. Seasonal expansion of the H corona and possible changes in thermospheric O/CO2 density ratios could independently shift the EMUS baselines, particularly for H Lyman-alpha. Since the EMUS disk observations are the primary evidence for the 'horizontally extensive' and 'planetary-scale' response across latitude, longitude, and local time, a seasonal","section":null},{"comment":"Section 4 (Discussion), paragraph on the oxygen emission ratio: The attribution of the oxygen dayglow enhancement specifically to electron-impact excitation rests on the [O(3S)130.4/O(5S)135.6] ratio as a clean diagnostic. The paper states that this ratio 'serves as a diagnostic of photon-driven versus particle-driven processes,' but the ratio also depends on neutral density profiles (O and CO2), solar EUV flux, and electron energy spectra simultaneously. The authors note that EUV did not increase (Figure S7), which is important, but they do not address whether ICME-induced changes in neutral O/CO2 density ratios (e.g., from atmospheric compression or heating) could independently shift the emission ratio. A brief discussion of this potential degeneracy, or a quantitative argument for why neutral density changes are expected to be secondary, would strengthen the attribution claim.","section":null}],"minor_comments":[{"comment":"Section 3, Figure 2 caption: The caption states that green curves represent orbit 21225, but the text refers to this orbit as showing the strongest ICME impact. Clarifying the UT timing of orbit 21225 in the caption would help readers cross-reference with the EMUS observation time.","section":null},{"comment":"Section 3, paragraph on EMUS observations: The text states that the EMUS event observation 'closely coincided with IUVS observations from orbit 21225.' The time difference is ~30 minutes (09:29 UT vs 09:59 UT). A brief note on whether the solar wind conditions were stable over this 30-minute window would strengthen the near-simultaneous claim.","section":null},{"comment":"Section 4: The reference to 'Hughes et al. (2024)' in the paragraph on proton aurora does not appear in the reference list. The closest entries are Hughes et al. (2023, 2025, 2026). Please verify and correct.","section":null},{"comment":"Section 4: The phrase 'simultaneously enhanced proton-driven and electron-driven excitation pathways' could be tightened. The two pathways operate on different species (H vs O) and are not strictly simultaneous in the sense of coupled processes. Clarifying that they operate concurrently but independently would improve precision.","section":null},{"comment":"Figure 4: The SZA bin labels in the legend are not fully legible. Consider enlarging the legend or listing the SZA bins in the figure caption.","section":null},{"comment":"Section 2: The quiet-time orbit selection criteria are described briefly. Stating the exact SZA matching tolerance and spatial overlap threshold used for selecting quiet-time orbits would strengthen the methodology.","section":null},{"comment":"References: Several references have 2026 publication dates (Parrott et al., 2026; Pranjali et al., 2026; Hughes et al., 2026; Sharma et al., 2026). If these are accepted/in-press, please verify final citation details (volume, page, DOI) before publication.","section":null}],"recommendation":"minor_revision","confidential_remarks":"The seasonal confound in the EMUS baseline (Major Comment 1) is the most substantive concern. The IUVS limb comparison is well-controlled (consecutive orbits, hours apart), so the vertical enhancement claim is robust. However, the 'planetary-scale' framing depends materially on the EMUS disk comparison, which has a ~4-week seasonal gap. If the authors can show that the EMUS enhancement magnitude is too large to be explained by seasonal drift alone (e.g., by citing typical seasonal variability amplitudes from prior studies), or if they can identify an alternative quiet-time EMUS scan closer in Ls, the horizontal-extent claim would be substantially strengthened. This is addressable within revision and does not undermine the core observational findings."},"author_rebuttal":null,"desk_editor":{"model":"glm-5.2","letter":"The main thing to know: this paper coordinates MAVEN/IUVS limb profiles with EMM/EMUS disk images during the May 2024 ICME, giving both vertical and horizontal views of the UV dayglow response. That dual-instrument, near-simultaneous setup is genuinely new for Mars dayglow studies, and the core observational result — all three emissions (H Lyman-α, O 130.4 nm, O 135.6 nm) brightened during the ICME — is solid. Two independent instruments confirming the same enhancement is real evidence, not circular reasoning. The IUVS side is well-controlled: quiet and event orbits are consecutive (21212–21218 vs. 21219–21227), so seasonal drift is negligible there. The oxygen line ratio diagnostic ([O 130.4/O 135.6] dropping below unity) is borrowed from Ritter et al. (2019) and Soret et al. (2024), and the authors check that solar EUV didn't increase (Figure S7), which rules out the most obvious confound for the ratio shift. Credit where due: the observational architecture is thoughtful and the EUV check matters. The soft spot is the EMUS baseline. The quiet-time EMUS disk scan is from 20 April 2024; the event scan is 18 May 2024. That's roughly four weeks, during which Mars moved from Ls ~240° to ~270° — approaching southern summer solstice. The paper itself notes that Ls ~270° is when the hydrogen corona expands and proton aurora peaks. So the EMUS 'quiet' baseline for H Lyman-α may already be biased low due to seasonal corona growth, not just ICME forcing. This matters because the EMUS disk observations are the primary evidence for the 'horizontally extensive' and 'planetary-scale' framing — the part that distinguishes this work from prior single-instrument limb studies. The IUVS vertical enhancement would survive without EMUS, but the planetary-scale claim depends on the disk comparison being clean. The mechanistic attribution to electron-impact excitation via the oxygen ratio is reasonable but not airtight: ICME-driven neutral density or O/CO2 compositional changes could independently shift the ratio, and no neutral density modeling is offered to close that gap. These are fixable issues — an averaged EMUS baseline from multiple quiet scans at comparable Ls, or at minimum an explicit acknowledgment of the seasonal confound, would strengthen the horizontal-extent claim substantially. This is a paper for space-physics researchers working on Mars thermospheric response to solar transients. It deserves a serious referee who can push on the baseline selection and ask for the supplementary figures in full resolution.","headline":"Genuine two-instrument ICME dayglow result, but the 'planetary-scale' framing leans on a seasonally confounded EMUS baseline.","tokens_in":16690,"tokens_out":644,"would_cite":false,"duration_ms":70903,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["96.50.sh","96.30.Dz","94.05.Dd"],"model":"glm-5.2","headline":"Solar storm lit up Mars's entire upper atmosphere at once","keywords":["Mars","UV dayglow","ICME","proton aurora","electron precipitation","thermosphere","MAVEN","EMM"],"falsifier":"If the [O(3S)130.4/O(5S)135.6] ratio were shown to be comparably sensitive to ICME-induced changes in neutral O/CO2 density ratios or atmospheric temperature structure as it is to electron precipitation, then the attribution of the oxygen enhancement to electron-impact excitation would become ambiguous, and the paper's central claim about simultaneous proton and electron mechanisms would need to be re-examined.","tokens_in":15795,"feed_emoji":"☀️","tokens_out":1415,"duration_ms":130012,"temperature":0.7,"pith_summary":"When a major interplanetary coronal mass ejection struck Mars in May 2024, it simultaneously intensified all three of the planet's main ultraviolet dayglow emissions—hydrogen Lyman-alpha and two atomic oxygen lines at 130.4 and 135.6 nm—across a planetary-scale region spanning the full vertical depth of the thermosphere and broad horizontal ranges of latitude, longitude, local time, and solar zenith angle. By combining near-simultaneous limb profiles from one spacecraft with disk images from another, the authors show that the event did not merely create a localized auroral patch but amplified existing dayglow structures everywhere at once. The concurrent brightening of hydrogen (driven by proton precipitation via charge-exchange producing energetic neutral atoms) and oxygen emissions (driven by electron-impact excitation from solar wind and solar energetic particle electrons) demonstrates that both proton and electron excitation pathways operated simultaneously during the ICME. A key diagnostic is the ratio of the two oxygen lines: because the 130.4 nm line is normally dominated by solar photon scattering while the 135.6 nm line is almost entirely electron-impact excited, a drop in their ratio below unity during the event signals a shift toward particle-driven excitation. The ratio fell to approximately 0.5 at peak ICME intensity, and solar EUV flux did not increase, ruling out enhanced illumination as the cause and pointing to energetic electron precipitation as the amplifier. Crucially, the characteristic peak altitudes and spatial distribution patterns of all three emissions remained essentially unchanged—the ICME intensified the brightness without reorganizing the atmospheric structure.","feed_headline":"Solar storm lit up Mars's entire upper atmosphere at once","feed_subtitle":"A May 2024 ICME simultaneously intensified hydrogen and oxygen UV emissions across the whole planet, revealing dual proton-electron excita","key_machinery":"The diagnostic machinery rests on three pillars. First, the H Lyman-alpha enhancement traces the proton aurora mechanism: solar wind protons charge-exchange with exospheric hydrogen to produce energetic neutral atoms that precipitate and excite hydrogen emissions. Second, the oxygen emissions trace electron-driven excitation: the O(5S) 135.6 nm line is 95% electron-impact excited while O(3S) 130.4 nm is 80-85% resonant scattering, so their ratio [130.4/135.6] serves as a clean diagnostic of photon-versus-particle dominance. A ratio dropping to ~0.5 during peak ICME, combined with no increase in solar EUV flux, isolates electron precipitation as the driver. Third, the near-simultaneous limb (","core_discovery":"The central finding is that an intense ICME produces a planetary-scale, vertically and horizontally extensive enhancement of Martian UV dayglow through the simultaneous operation of proton-driven and electron-driven excitation mechanisms, with the oxygen emission line ratio serving as the key diagnostic that distinguishes particle-driven from photon-driven excitation. The ICME amplified existing emission structures rather than creating new ones.","pith_inferences":["If the ICME primarily amplifies existing structures rather than reorganizing them, this suggests the Martian thermosphere's basic circulation and composition patterns are robust to even extreme transient forcing—a property that would simplify predictive modeling of space-weather impacts.","The broadening of the oxygen emission peak from ~120-140 km to ~100-160 km without a shift in peak altitude could be used to invert for the precipitating electron energy spectrum, since different electron energies deposit at different altitudes; this event's broadening implies a wide energy spectrum from hundreds of eV to tens of keV.","The fact that the strongest enhancement occurred during southern summer (Ls ~270°), when the hydrogen corona is most extended, raises the question of whether ICME impacts during other seasons would produce qualitatively different responses—particularly whether proton aurora would be suppressed when the corona is contracted.","If the [130.4/135.6] ratio depends on neutral O/CO2 density ratios that themselves change during ICME compression of the atmosphere, then the ratio's interpretive power as a pure electron-precipitation diagnostic may be partially degenerate with neutral composition changes."],"forward_implications":["If the oxygen line ratio is a reliable real-time diagnostic of electron precipitation energy and flux, it could serve as a remote-sensing proxy for thermospheric space-weather monitoring at Mars without requiring in-situ particle detectors.","The planetary-scale nature of the response implies that future Mars missions planning atmospheric entry or aerobraking during solar maximum should anticipate thermospheric density and composition perturbations across the entire dayside, not just near the subsolar point.","The simultaneous proton and electron excitation during a single ICME suggests that coupled ion-neutral-electron models of the Martian upper atmosphere need to treat both precipitation channels together rather than in isolation.","The persistence of enhancement toward the terminator and the observed day-to-night transport signature suggest that ICME-driven space weather modifies the nightside ionosphere through enhanced plasma transport, which could affect radio communication and radar sounding on the nightside."],"fun_headline_variants":["May 2024 ICME amplified Martian UV dayglow across the whole planet","Martian hydrogen and oxygen UV emissions surged simultaneously during ICME","ICME triggered planet-wide Martian dayglow via dual proton-electron excitation","Coordinated MAVEN and EMM observations capture planetary-scale Martian dayglow surge","Intense solar transient intensified existing Martian UV emissions vertically and horizonta"],"cache_read_input_tokens":0,"weakest_assumption_plain":"The paper attributes the oxygen dayglow enhancement specifically to electron-impact excitation based on the [O(3S)130.4/O(5S)135.6] ratio dropping below unity, treating this ratio as a clean diagnostic of particle-driven versus photon-driven processes. This ratio, however, also depends on neutral density profiles and atmospheric composition, both of which an ICME could alter through compression or heating independently of electron precipitation.","fun_headline_variants_meta":{"raw":{"variants":["May 2024 ICME amplified Martian UV dayglow across the whole planet","Martian hydrogen and oxygen UV emissions surged simultaneously during ICME","ICME triggered planet-wide Martian dayglow via dual proton-electron excitation","Coordinated MAVEN and EMM observations capture planetary-scale Martian dayglow surge","Intense solar transient intensified existing Martian UV emissions vertically and horizontally"]},"model":"glm-5.2","effort":"low","cost_usd":0.0,"raw_usage":{"total_tokens":627,"prompt_tokens":530,"completion_tokens":97,"prompt_tokens_details":null},"tokens_in":530,"tokens_out":97,"duration_ms":64739,"temperature":1.0,"reasoning_tokens":null,"cache_read_input_tokens":0,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-07-09T21:41:04.182432+00:00","model_set":{"reader":"glm-5.2"},"falsifier":"If the [O(3S)130.4/O(5S)135.6] ratio were shown to be comparably sensitive to ICME-induced changes in neutral O/CO2 density ratios or atmospheric temperature structure as it is to electron precipitation, then the attribution of the oxygen enhancement to electron-impact excitation would become ambiguous, and the paper's central claim about simultaneous proton and electron mechanisms would need to be re-examined.","supporting_citations":[],"review_version":1}