{"id":"ebd65891-7e40-450c-b883-bb7e5cd88195","arxiv_id":"2501.01009","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"He I 1083 nm emission seen during the 2024 total eclipse appears on the lunar disc with chromospheric line widths, indicating terrestrial scattering of the flash spectrum rather than coronal neutral helium.","lead":"Using a new near-infrared spectrograph during the April 8, 2024 total solar eclipse, the authors detected the helium line at 1083 nm both in the corona and in front of the lunar disc, with a line width matching cool chromospheric gas rather than million-degree coronal plasma.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The terrestrial-scattering attribution at 1083 nm is asserted without the quantitative intensity comparison that would make it load-bearing; the non-coronal detection itself is more secure.","rationale":"The reader's weakest assumption identifies the same load-bearing gap: the paper attributes the He I 1083 signal to terrestrial atmospheric scattering without a quantitative model at 1083 nm, where the Rayleigh mechanism established for blue lines is far weaker. This is the correct focus. The central negative claim - that the observed signal challenges the inference of abundant neutral helium in the corona - is supported by the independent spatial control: He I 1083 and Paschen-gamma are detected on the lunar disc, where no direct coronal emission can originate, while Fe XIII 1074.7 nm is confined above the limb. The instrument-scattered-light and camera-bleed checks in Section 3 are plausible, and the wavelength coincidence with the expected lines is a useful consistency check. Thus the paper does not deserve rejection. However, the title and abstract go beyond the secure negative result by naming a specific atmospheric mechanism, and they do so without deriving an expected scattered intensity or comparing it to the measurement. Stellmacher and Koutchmy (1974) is a blue-line study; extrapolating to 1083 nm requires either a quantitative Rayleigh calculation or an explicit aerosol/cloud scattering model, neither of which appears. The absence of radiometric calibration compounds this: the paper cannot state absolute intensities, so it cannot test the scattering hypothesis against a synthetic prediction. Because the paper itself uses language such as 'we hypothesize' in the abstract, the appropriate verdict is CONDITIONAL, matching the reader's assessment. A single concrete computation of the expected 1083 nm scattered signal would settle whether the title's scattering attribution is credible or should be softened to a non-coronal but mechanism-unspecified result.","tokens_in":11811,"tokens_out":8580,"duration_ms":86857,"concrete_test":"Compute the expected 1083 nm scattered intensity using the observed flash-spectrum radiance (from the atlas-calibrated on-disc spectra in Figure 3e), the Rayleigh and Mie/aerosol optical depths at 1083 nm for the Dardanelle site including the thin high cloud cover reported in Section 2.2, and the double-scattering geometry of Stellmacher and Koutchmy (1974). Compare this predicted intensity with the measured He I 1083 counts on the lunar disc in Figure 4c after performing a radiometric calibration of the detector. If the predicted signal is more than an order of magnitude below the observed signal, the specific terrestrial-scattering origin asserted in the title is unsupported, even though the non-coronal conclusion would remain intact.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's title and abstract assert that the observed He I 1083 signal arises from terrestrial atmospheric scattering of the solar flash spectrum, but neither Section 3 nor Section 4 computes the scattered intensity this mechanism would produce at 1083 nm. The only quantitative anchor is Stellmacher and Koutchmy (1974), whose line-width versus wavelength relation was established for blue chromospheric lines. Rayleigh scattering scales as lambda^-4: relative to 400 nm, the cross section at 1083 nm is lower by about (400/1083)^4 ~ 1.8e-2, and the paper introduces no aerosol or cloud scattering component even though Section 2.2 reports thin high cloud cover during totality. The observational evidence that He I 1083 and Paschen-gamma appear on the lunar disc while Fe XIII 1074.7 nm appears only above the limb is a strong control, and the instrumental-scattering checks in Section 3 are reasonable. Those data do support a non-coronal, scattered component, and the central negative claim - that the eclipse signal is not evidence for abundant coronal neutral helium - is likely robust. However, the specific positive attribution to double scattering of the flash spectrum, which is the title claim, remains a hypothesis because no expected signal level is derived and compared with the measured counts and spatial gradient. A detector artefact from the 12-bit dynamic-range compression is partially excluded, but the line-width argument would also be stronger if the compression's effect on the fitted widths were quantified.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript describes near-infrared slit-spectrograph observations of the solar corona and lunar disc made with the new CHEESE instrument during the April 8, 2024 total solar eclipse from Dardanelle, Arkansas. During totality the authors detect Fe XIII 1074.7 nm only above the lunar limb, while He I 1083 nm and H I 1093.8 nm Paschen-gamma appear both in the corona and on the lunar disc. Gaussian fits give chromospheric-scale line widths for He I 1083 and coronal-scale widths for Fe XIII 1074.7 nm. Instrumental checks (a detector region not imaging the slit, laboratory bleed tests, on-disc scattered-light estimates) are used to argue against camera bleed and internal scattering. The authors conclude that the He I 1083 signal is not of coronal origin and hypothesize, following Stellmacher and Koutchmy (1974), that it arises from terrestrial atmospheric double scattering of the chromospheric flash spectrum.","tokens_in":12018,"tokens_out":2878,"duration_ms":30494,"significance":"If the result holds, it directly challenges the interpretation of earlier eclipse detections of 'diffuse' coronal He I 1083 as evidence for abundant neutral helium in the corona, and it sharpens the ongoing debate about the origin of this line in eclipse observations. The paper's main observational strengths are the simultaneous detection of a genuinely coronal line (Fe XIII 1074.7 nm) that is absent on the lunar disc, the on-disc calibration validating the spectral resolution, the spatial control provided by the non-slit region of the detector, and the public release of instrument designs and data. The central negative claim—that the observed He I 1083 is not evidence for coronal neutral helium—is well supported by the differential behavior of the three lines. The specific positive attribution to terrestrial atmospheric scattering is, however, asserted rather than quantitatively demonstrated, and this is the main weakness relative to the title claim.","major_comments":[{"comment":"The title and abstract assert that the observations support a terrestrial atmospheric scattering origin for He I 1083, but no quantitative test of this mechanism is provided at 1083 nm. The comparison to Stellmacher and Koutchmy (1974) concerns blue chromospheric lines; Rayleigh scattering scales as lambda^-4, so the cross section at 1083 nm is roughly two orders of magnitude smaller than at 400 nm. Section 2.2 reports thin high cloud cover during totality, and the manuscript introduces no aerosol or cloud scattering component. To make the scattering attribution load-bearing, the authors should compute the expected scattered He I 1083 intensity (and its spatial gradient along the slit) from the flash-spectrum geometry and compare it with the observed counts, or explicitly quantify why the double-scattering mechanism remains efficient in the near-IR.","section":"Abstract and Section 3, final paragraph"},{"comment":"The camera's onboard processing reduced the effective dynamic range to 12 bits while the slit crossed bright chromospheric material, and the paper states that weak coronal signals fell outside the effective dynamic range. The line widths in Figure 4(f) are fitted from data taken in this regime. Because the measured chromospheric width of He I 1083 is a central discriminator, the manuscript needs to show that the dynamic-range compression does not significantly distort the fitted Gaussian widths and amplitudes, for example by injecting synthetic line profiles through the same onboard processing or by comparing widths measured before and after third contact when the illumination changed.","section":"Section 3, dynamic-range discussion and Figure 4(f)"},{"comment":"The claim that the He I 1083 intensity increases toward the closest location of the flash spectrum is presented qualitatively. Given that this spatial gradient is one of the three pieces of evidence for the atmospheric-scattering hypothesis, it should be quantified: the authors should fit the intensity variation along the slit against the angular distance to the flash-spectrum source, and compare that gradient with the prediction of the proposed scattering model. As written, the gradient is consistent with the hypothesis but does not distinguish it from other non-coronal mechanisms.","section":"Section 3 and Figure 4(e)-(f)"}],"minor_comments":[{"comment":"The phrase 'an anomalous vertical column shift (along the slit) on the left side of the detector' is unclear; it should specify whether the shift is in the dispersion direction or the slit direction, and how it was determined.","section":"Section 2.2"},{"comment":"The caption contains an incomplete sentence, 'In total we had.' This appears to be a leftover from an earlier draft and should be removed or completed.","section":"Figure 4 caption"},{"comment":"The sentence 'There are a few other plausible explanations for our observation, which need to be addressed in detail before rejected' should read 'before being rejected' or 'before they are rejected.'","section":"Section 4"},{"comment":"The reference to 'the previously observed lines of CaIIion in the blue part of the spectrum Migeotte & Rosen (1955)' is missing a comma and would benefit from a parenthetical citation format consistent with the rest of the text.","section":"Section 4"},{"comment":"The text says the same reduction steps were applied 'as for the data shown in Figure 1,' but the on-disc calibration data are shown in Figure 3; the cross-reference should be corrected.","section":"Section 3"},{"comment":"The predicted spectral resolution is quoted as R~9,600, while the on-disc calibration yields R~7,000; the paper should briefly explain the difference (for example, slit width, seeing, or focus) so that readers do not interpret it as an inconsistency.","section":"Section 2.1"}],"recommendation":"major_revision","confidential_remarks":"The paper is a good fit for Solar Physics and the observational controls are well designed. My main concern is the gap between the title's positive attribution ('terrestrial atmospheric scattering') and the level of quantitative support in the text; the non-coronal conclusion is much better supported than the specific scattering mechanism. I would encourage the editor to request the quantitative intensity estimate described in Major Comment 1 before publication, since it is directly testable and would substantially increase the value of the paper. The dynamic-range issue in Major Comment 2 is standard for ground-based eclipse spectroscopy but should be addressed explicitly rather than left implicit."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Two things to know up front.\n\nFirst, the observational core is solid and likely correct. CHEESE simultaneously saw He I 1083 and Paschen-gamma on the lunar disc, with chromospheric line widths, while the coronal Fe XIII 1074.7 line appeared only above the limb. That is a coherent set of controls, and it is hard to escape the conclusion that the He I 1083 seen during totality was not emitted by coronal neutral helium. If this holds, the eclipse detections of Kuhn, Dima, and Judge stop being evidence for abundant neutral helium, and the modeling and Hanle magnetometry programs built on that signal need a rethink.\n\nSecond, the title and abstract oversell the mechanism. The specific attribution to terrestrial double scattering of the flash spectrum is asserted without any calculation of the expected scattered intensity at 1083 nm. Rayleigh scattering at that wavelength is down by roughly two orders of magnitude from the blue lines Stellmacher and Koutchmy studied, and the thin high cloud cover is not folded in. The paper labels the mechanism a hypothesis in the abstract and conclusions, so the gap is acknowledged, but 'evidence for' in the title goes further than the analysis does.\n\nWhat the paper does well: the instrument is purpose-built, the disc calibration validates the wavelength solution, and the authors took care to rule out camera bleed and in-spectrograph scattered light. The combination of lunar disc detection, chromospheric thermal width, and the Fe XIII control is a genuinely new evidence set.\n\nThe soft spots are real but not fatal. The scattering mechanism needs a quantitative intensity comparison; otherwise the paper should read as 'non-coronal origin' without specifying the terrestrial scattering contribution. The camera's dynamic range compression is discussed but its effect on the fitted widths is not quantified, and the width is a key diagnostic. Minor editorial defects (an incomplete sentence, some typos) are easy to fix.\n\nRecommendation: this deserves peer review. A referee should ask for the scattering estimate and a dynamic-range check of the line widths, but the central negative claim is likely robust and this is a paper the community needs.","headline":"Solid observational case against coronal He I 1083, but the title's scattering mechanism is a hypothesis without a quantitative estimate.","tokens_in":12710,"tokens_out":3679,"would_cite":true,"duration_ms":33381,"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":"April 2024 eclipse data show the coronal helium line comes from Earth's atmosphere, not the Sun.","keywords":["He I 1083 nm","total solar eclipse","coronal helium","terrestrial atmospheric scattering","eclipse spectroscopy","near-infrared spectrograph","neutral helium corona","Paschen-gamma"],"falsifier":"Observe the same spectral region from a platform above most of Earth's atmosphere, such as a high-altitude balloon, during a future totality: if the 1083 nm signal on the lunar disc and in the corona disappears, the terrestrial scattering origin is confirmed; if it persists with coronal brightness, the solar-origin hypothesis is revived. A simpler test is to compute the expected Rayleigh-scattered intensity at 1083 nm under the eclipse geometry and compare it to the measured signal.","tokens_in":11510,"feed_emoji":"🌑","tokens_out":5063,"duration_ms":41839,"temperature":0.7,"pith_summary":"A dedicated near-infrared spectrograph observed the April 8, 2024 total solar eclipse and detected the helium line at 1083 nm both above the lunar limb and on the lunar disc. The paper argues that the line's presence on the lunar disc, its chromospheric thermal width, and its brightening toward the flash spectrum show it is sunlight scattered by Earth's atmosphere, not neutral helium in the corona. If correct, earlier eclipse detections of this line do not support the idea of abundant neutral helium in coronal plasma.","feed_headline":"Eclipse helium line traced to Earth's atmosphere, not the corona","feed_subtitle":"New spectrograph data challenge decades of eclipse evidence for neutral helium in the solar corona.","key_machinery":"The central object is the CHEESE slit spectrograph, whose 1 cm slit spans 58 arcminutes so it images the lunar disc and the corona simultaneously. The load-bearing physical mechanism is the double-scattering of the solar flash spectrum by Earth's atmosphere, previously demonstrated for blue chromospheric lines; the paper's evidence consists of the co-spatial appearance of He I 1083 and H I Paschen-γ on the lunar disc, their chromospheric line widths, and the intensity gradient toward the flash spectrum location at third contact.","core_discovery":"The paper reports that CHEESE, a new grating spectrograph built for this purpose, detected the He I 1083 nm line, the Fe XIII 1074.7 nm coronal line, and the H I Paschen-γ 1093.8 nm chromospheric line during totality on April 8, 2024. The Fe XIII line appears only above the lunar limb, as a true coronal signal should, while the He I and H I lines appear both above the limb and on the lunar disc, with a thermal width corresponding to roughly $10^{5}$ K rather than coronal temperatures, and with intensity increasing toward the part of the sky nearest the flash spectrum. The authors conclude that the He I signal is not solar coronal emission but terrestrial atmospheric scattering of chromospheric flash-spectrum radiation, and that this removes the main eclipse-based evidence for abundant neutral helium in the corona.","pith_inferences":["The same scattering contamination should affect other strong near-infrared chromospheric lines, such as the Paschen series, so eclipse spectra using those lines may need a similar subtraction.","Because elastic scattering preserves line width, the chromospheric thermal width of the detected He I line cannot by itself distinguish a solar from an atmospheric origin; the decisive evidence is spatial and temporal, not spectral.","The measured intensity gradient along the slit could be used to constrain the scattering phase function of the terrestrial atmosphere at 1083 nm, giving a quantitative test of the proposed mechanism.","If confirmed, the result would imply that reported coronal neutral-helium abundances from eclipse data are upper limits set by atmospheric scattering, shifting models of helium ionization in the corona."],"forward_implications":["If the scattering origin is right, previous eclipse detections of 'diffuse' coronal He I 1083 no longer count as evidence of neutral helium in the corona.","He I 1083 cannot be used as a routine Hanle-effect coronal magnetometry diagnostic until the atmospheric contamination is removed or avoided.","Eclipse observations of near-infrared chromospheric lines must include a sky-scattering correction and be interpreted with flash-spectrum geometry in mind.","The Fe XIII 1074.7 nm line, detected only above the limb, remains a clean coronal signal in the same data set.","A balloon- or space-based eclipse observation can settle the question by measuring the line above the scattering atmosphere."],"supporting_citations":[{"why":"Supplied the original eclipse detection of 'diffuse' coronal He I 1083 that the paper sets out to test.","marker":"Kuhn et al. 1996"},{"why":"A subsequent eclipse campaign that confirmed the extended He I 1083 signal and set the line-width expectation the paper compares against.","marker":"Dima et al. 2016"},{"why":"A recent eclipse detection whose brightening toward second and third contacts the paper cites as agreement with the atmospheric scattering hypothesis.","marker":"Judge et al. 2019"},{"why":"The eclipse experiment that established the double-scattering mechanism for chromospheric lines, which the paper invokes as the origin of its He I signal.","marker":"Stellmacher & Koutchmy 1974"},{"why":"Modeling work predicting bright lower-coronal He I 1083 that sharpens the puzzle but cannot explain extended emission.","marker":"Del Zanna et al. 2020"},{"why":"Provides the equation the paper uses to convert measured line widths to plasma temperatures.","marker":"Schad et al. 2024"}],"fun_headline_variants":["Eclipse helium signal actually from Earth's sky, not corona","He I 1083 during eclipse is atmospheric scattering, not solar","Eclipse helium line is Earth's atmosphere, study shows","New data: eclipse helium comes from atmosphere, not corona","Coronal helium claim refuted: it's atmospheric glow"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The whole terrestrial-scattering explanation rests on the assumption that the double-scattering process demonstrated for blue chromospheric lines also operates at 1083 nm with enough efficiency to produce the observed signal, an efficiency the paper does not compute.","fun_headline_variants_meta":{"raw":{"variants":["Eclipse helium signal actually from Earth's sky, not corona","He I 1083 during eclipse is atmospheric scattering, not solar","Eclipse helium line is Earth's atmosphere, study shows","New data: eclipse helium comes from atmosphere, not corona","Coronal helium claim refuted: it's atmospheric glow"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000204,"raw_usage":{"total_tokens":1387,"prompt_tokens":938,"completion_tokens":449,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":554,"completion_tokens_details":{"reasoning_tokens":365}},"tokens_in":554,"tokens_out":449,"duration_ms":4493,"temperature":1.0,"reasoning_tokens":365,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T22:38:51.595677+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Observe the same spectral region from a platform above most of Earth's atmosphere, such as a high-altitude balloon, during a future totality: if the 1083 nm signal on the lunar disc and in the corona disappears, the terrestrial scattering origin is confirmed; if it persists with coronal brightness, the solar-origin hypothesis is revived. A simpler test is to compute the expected Rayleigh-scattered intensity at 1083 nm under the eclipse geometry and compare it to the measured signal.","supporting_citations":[{"cited_title":"R., Penn , M","cited_arxiv_id":null,"evidence_quote":"Supplied the original eclipse detection of 'diffuse' coronal He I 1083 that the paper sets out to test."},{"cited_title":"2016, Frontiers in Astronomy and Space Sciences , 3, 13, 10.3389/fspas.2016.00013","cited_arxiv_id":null,"evidence_quote":"A subsequent eclipse campaign that confirmed the extended He I 1083 signal and set the line-width expectation the paper compares against."},{"cited_title":"2019, , 877, 10, 10.3847/1538-4357/ab0e04","cited_arxiv_id":null,"evidence_quote":"A recent eclipse detection whose brightening toward second and third contacts the paper cites as agreement with the atmospheric scattering hypothesis."},{"cited_title":"1974, , 35, 43","cited_arxiv_id":null,"evidence_quote":"The eclipse experiment that established the double-scattering mechanism for chromospheric lines, which the paper invokes as the origin of its He I signal."},{"cited_title":"A., Fehlmann , A., Dima , G","cited_arxiv_id":null,"evidence_quote":"Provides the equation the paper uses to convert measured line widths to plasma temperatures."}],"review_version":1}