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REVIEW 3 major objections 5 minor 3 references

Climatology of Mars Topside Ionosphere during Solar Cycles 24 and 25 using MAVEN Dataset of 2015-2024

T0 review · 3 major / 5 minor · reviewed 2026-08-06 · deepseek-v4-flash

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Pith's one-line read Ten years of MAVEN observations show the Mars topside ionosphere growing denser with solar activity, with electron densities 2 to 5 times higher and the O+ peak 40-50 km higher during the maximum of Solar Cycle 25 than during quiet phases.

desk verdict Useful first multi-phase MAVEN topside climatology; qualitative solar-cycle pattern is solid, but the enhancement factors need bootstrapped errors and sampling controls before they should be quoted. read the letter →

arxiv 2507.02368 v1 pith:7NWRCAES submitted 2025-07-03 physics.space-ph

Lot Ram , Chanchal Singh , Diptiranjan Rout , Aadarsh Raj Sharma , Sumanta Sarkhel This is my paper · ORCID
classification physics.space-ph
keywords MarsionospheretopsidesolarcycleMAVENirradianceO+peakaltitudeplanetaryclimatology
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper tries to establish a solar-cycle climatology for the upper ionosphere of Mars, using ten years of MAVEN in-situ measurements (2015-2024, Martian years 32-38) over the northern hemisphere. It sorts the data into four phases of Solar Cycles 24 and 25 and compares median altitude profiles of electrons and seven ion species from 150 to 500 km. The central finding is that plasma densities are largest during the maximum phase of Solar Cycle 25: dayside electron density is 2 to 5 times higher, molecular ions are 1.1 to 13 times higher, and the O+ peak is 1.9 to 2.5 times denser and sits 40-50 km higher than in low-activity phases. If correct, this means solar irradiance is the dominant controller of the topside ionosphere on solar-cycle timescales, with the nightside strengthened by transport and electron-impact ionization that are more effective at high activity.

What carries the argument

The central machinery is the four-phase solar-cycle binning and the median altitude profiles built from MAVEN's Langmuir Probe and Waves (LPW) electron densities and Neutral Gas and Ion Mass Spectrometer (NGIMS) ion densities. The four phases are defined by monthly sunspot number: SC24 descending (SSN 16-93), SC24 minima (SSN 1.6-0.6), SC25 ascending (SSN 14-75), and SC25 maxima (SSN > 96). Comparison of these median profiles carries the argument, with the proposed mechanism being that elevated EUV/SXR irradiance during maxima heats and inflates the neutral atmosphere, increasing photoionization on the dayside, while the inflated dayside acts as a reservoir whose outflow plus electron-impact ionization from solar wind electrons sustains a denser nightside.

What would settle it

Move one of the phase boundaries by six months and recompute the median profiles; if the reported 2-5x electron density enhancement of the SC25 maximum phase disappears, the result is an artifact of binning. Alternatively, measure electron density in the 150-200 km altitude range during SC25 maxima with an instrument that still samples that range, since MAVEN stopped doing so after August 2020, and check whether the enhancement actually extends down to those altitudes.

Watch

Extended reading notes

Core claim

The paper reports that, over the northern hemisphere (0-60°N) and outside strong crustal magnetic fields, the topside ionosphere of Mars varies systematically with the phase of the solar cycle. Median densities of electrons and of CO2+, O2+, NO+, OH+, O+, N+, and C+ are highest during the maxima phase of Solar Cycle 25 on both day and night sides, with dayside values 1-2 orders of magnitude above nightside values. Electron density is enhanced by factors of 2-5, molecular ions by 1.1-13, and the O+ peak density by 1.9-2.5 times with a 40-50 km upward shift of its peak altitude compared to low-activity phases. The authors attribute the dayside enhancement to EUV and soft X-ray fluxes that are 1.4-2 and 1.5-6 times higher, respectively, and the nightside enhancement to elevated solar electron flux (33-66% higher) and stronger day-to-night plasma transport. They also note that low-latitude (0-30°N) densities generally exceed mid-latitude (31-60°N) densities, and that averaged topside electron density tracks EUV and IMF variations more closely than solar wind dynamic pressure.

Load-bearing premise

The division of the MAVEN record into four solar-cycle phases using monthly sunspot-number thresholds, especially the SC25 maxima cutoff at SSN > 96, is the load-bearing choice, because the enhancement factors are ratios of median profiles between these bins, and the post-August-2020 periapsis raise means the later phases lack data below 180-220 km that the earlier phases include.

Editorial extensions

If this is right

  • The phase-resolved median profiles provide a quiet-time baseline that future studies can subtract from transient space-weather events to isolate their effects on Mars's ionosphere.
  • Mars's topside ionosphere can be modeled as strongly irradiance-controlled on solar-cycle timescales, meaning solar-flux forecasts translate into ionospheric density predictions.
  • The 40-50 km rise in the O+ peak altitude implies that the neutral composition (O/CO2 ratio) in the upper atmosphere shifts substantially between solar minimum and maximum, with implications for atmospheric escape rates.
  • The nightside density increase during maxima indicates that transport and electron-impact ionization become more effective at high activity, so global circulation models must include solar-cycle-dependent nightside sources.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The enhancement factors may be partly an artifact of the post-2020 periapsis raise: the ascending and maxima phases lack data below 180-220 km, while earlier phases include them, so the 150-200 km comparisons are not on equal footing.
  • If the irradiance-driven trend holds, the topside ionosphere of Mars could serve as a calibrated solar-activity proxy at Mars, useful for reconstructing past solar cycles from future ionospheric data.
  • Because the southern hemisphere was excluded to avoid crustal fields, the paper's climatology is hemisphere-specific; the authors note the southern-hemisphere study is underway, and its results may find more localized, crustal-field-modulated responses.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 5 minor

Summary. This manuscript uses MAVEN LPW, NGIMS, SWIA, SWEA, MAG, and EUVM data from January 2015 to November 2024 to construct median altitude profiles (150–500 km) of electrons and seven ion species over Mars's northern hemisphere (0–60°N), separated into dayside (SZA < 60°) and nightside (SZA > 115°), and sorted into four manually defined phases of Solar Cycles 24–25. The central claim is that the topside ionosphere is densest during the SC25 maximum, with dayside electron densities increased by factors of 2–5, molecular ion densities by about 1.1–13, and O+ peak density by 1.9–2.5 accompanied by a 40–50 km peak-altitude rise, relative to low-activity phases; these changes are attributed to EUV/SXR irradiance increases (about 1.4–2 times) and, on the nightside, to day-to-night transport and electron-impact ionization by elevated solar electron fluxes.

Significance. The paper has clear strengths: it assembles a decade of MAVEN data, applies quiet-time filtering to remove ICMEs, CIRs, flares, SEPs, dust-storm periods, and strong crustal-field influences, and makes derived products available on Zenodo. If the reported enhancements are robust, the work would provide the first SC24–SC25 topside ionospheric climatology for Mars and a useful quiet-time baseline for space-weather studies. However, the headline enhancement factors are not yet demonstrated to the standard required by the journal because the phase comparison pools unequal SZA/Ls sampling and lacks uncertainty quantification; the scientific value therefore hinges on the revisions described below.

major comments (3)
  1. [Section 3.2, Figure 6] The phase comparison pools all dayside passes with SZA < 60° and all nightside passes with SZA > 115° over multi-year intervals, with no binning, weighting, or matching by SZA, solar longitude (Ls), Mars–Sun distance, or season. Figure 1b–d shows that MAVEN's periapsis precesses through the mission, so the SZA and Ls coverage is not balanced among the descending, minima, ascending, and maxima phases. Because topside densities vary strongly with SZA and season (through CO2 condensation, dust, and orbital distance), the reported 2–5× electron and 1.1–13× ion enhancements could be partly or wholly a sampling artifact. In addition, the acknowledged post-August-2020 periapsis raise from about 150 km to about 180–220 km (Section 3.1, Figure 4 caption) removes 150–200 km data from the ascending and maxima phases while those altitudes are present in the SC24 phases, directly biasing the 150–200 km segment of Figure 6. I request a homogenized comparison (for example, SZA/Ls-binned medians, matched-orbit subsampling, or regression controls) and a demonstration that the enhancement factors survive that control.
  2. [Section 3.2, Figure 6] The enhancement factors quoted in the text and abstract (electron 2–5×; CO2+ and O2+ 1.1–13×; O+ peak 1.9–2.5×; O+ peak altitude +40–50 km) are point values derived from median profiles without confidence intervals, significance tests, or propagation of the median absolute deviations shown in Figures 2–5. Because the numbers of orbits differ among phases and the MAD bars are large, each ratio needs an uncertainty estimate (for example, a bootstrap or percentile interval) before the quantitative claims in the abstract can be accepted.
  3. [Section 2, phase definitions] The four phase intervals are defined by hand-selected monthly SSN thresholds (for example, SC25 ascending 2020 October–2022 August with SSN 14–75, and maxima with SSN > 96), with no objective segmentation algorithm and no sensitivity test. Since the Figure 6 median profiles are integrated over these intervals, a small shift of a boundary would re-bin the profiles and change the reported enhancement ratios; please provide a sensitivity analysis over the phase-boundary choices or adopt an automated, fully specified phase-segmentation scheme.
minor comments (5)
  1. [Section 3.1, Figure references] The text refers to 'Figures 1b & Figures 1d-i' for density profiles and 'Figure 1g' for EUV flux, but Figure 1 is the orbit-coverage figure; these citations should instead point to the corresponding panels of Figures 2–6 and to Figure 1a.
  2. [Introduction] The citation 'J. K. Fox 1997' should be 'J. L. Fox 1997' to match the reference list and the author's name.
  3. [Section 2, data filtering] The text states that all ICME, CIR, flare, SEP, and dust-storm intervals were removed, but no table or figure reports the number of retained orbits or measurement-seconds per phase and altitude bin; such a table would help the reader judge the robustness of the median profiles.
  4. [Section 3.1, Figure 2] The statement that ion data are unavailable at low latitude between 200 and 350 km during the descending phase is an important coverage caveat for the latitudinal comparison; it should be repeated in the conclusions or in the figure caption rather than appearing only in the body text.
  5. [Abstract] The claim that this is 'for the first time' a long-term MAVEN study of the SC24–25 topside ionosphere is stronger than the literature review in the introduction supports; I recommend reframing this as the first systematic comparison spanning the descending-to-maxima phases rather than claiming novelty solely from the use of long-term MAVEN data.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the paper reports MAVEN density measurements and compares them with independently measured solar irradiance, solar wind, and electron flux data; no fitted parameter is renamed as a prediction.

full rationale

The paper is an observational climatology, not a derivation: it fits no model and computes no constants from the ionospheric densities. The central comparison (Section 3.2, Figure 6) is between MAVEN NGIMS/LPW density profiles binned by solar-cycle phase and independent measurements of EUV/SXR irradiance from EUVM, electron flux from SWEA, and IMF/solar wind from MAG/SWIA, with phases assigned from SILSO sunspot numbers. No quantity used as evidence is derived from the densities being explained; the quoted enhancement factors are medians of observed densities, and the attributed cause (elevated solar irradiance, Section 4) is measured separately. The paper's self-citations, such as Ram et al. 2023 for space-weather event catalogs and Ram et al. 2025 for the derived-data repository, are data-exclusion or data-availability references, not load-bearing mathematical or uniqueness arguments. The acknowledged periapsis-raise coverage gap and the lack of SZA/Ls homogenization are sampling-robustness concerns, not circularity: they affect whether the reported enhancement is real, not whether the explanation reduces to the input. No self-definitional, fitted-input-as-prediction, self-citation-chain, or ansatz-smuggling step was found.

Assumptions & free parameters 3 free parameters · 3 assumptions · 0 invented entities

The paper fits no model and introduces no new entities. Its central claim rests on analysis choices: the SSN-based phase boundaries, the SZA cutoffs, and the altitude binning, plus the representativeness of the filtered MAVEN data set. These choices are reasonable but not formally justified, so the quantitative density factors are approximate.

free parameters (3)
  • Solar cycle phase boundaries (SSN thresholds) = SC24 descending SSN 16-93; SC24 minima SSN 0.6-1.6; SC25 ascending SSN 14-75; SC25 maxima SSN >96
    Hand-chosen intervals from literature (Ouattara & Amory-Mazaudier 2009; Sawadogo et al. 2023). The phase medians and derived enhancement factors depend on where these cuts are placed.
  • Dayside and nightside solar zenith angle cutoffs = Dayside SZA < 60 degrees; nightside SZA > 115 degrees
    Chosen thresholds determine which observations enter the day and night composites; changing them changes the median profiles and factors.
  • Altitude bin width for median profiles = 10 km
    10 km bins with median absolute deviation; a wider or narrower bin changes profile shape and reported density factors.
assumptions (3)
  • domain assumption MAVEN periapsis sampling is representative of the northern hemisphere topside ionosphere over 150-500 km for each phase.
    The climatology is built from orbital tracks; periapsis altitude and local-time coverage vary, and after August 2020 altitudes below about 200 km are not sampled for the ascending and maxima phases.
  • domain assumption Deleting ICME, CIR, flare, SEP, and dust-storm periods yields a quiet-time baseline.
    Section 3 first paragraph; uses external catalogs (NASA CCMC DONKI, SDC, Guzewich et al. 2020, Martin-Rubio et al. 2024) without quantifying completeness or thresholds for each removal.
  • domain assumption The northern hemisphere is effectively free of strong crustal magnetic fields.
    Section 2; citation to Connerney et al. 2005; this justifies excluding southern hemisphere data and interpreting transport as pressure-gradient day-to-night flow.

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Cite this review

Pith. "Pith review of Climatology of Mars Topside Ionosphere during Solar Cycles 24 and 25 using MAVEN Dataset of 2015-2024." pith.science (2026). https://pith.science/paper/7NWRCAES

@misc{pith2026250702368,
  author       = {Pith},
  title        = {Pith review of: Climatology of Mars Topside Ionosphere during Solar Cycles 24 and 25 using MAVEN Dataset of 2015-2024},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/7NWRCAES}},
  note         = {Machine review of arXiv:2507.02368}
}
read the original abstract

The Mars ambient space environment evolves with the varying solar activity. Understanding the Martian space environment, particularly the topside ionosphere across different phases of Solar Cycles (SC) 24 \& 25 remains a key research gap in planetary ionospheric science. In this study, we utilized the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission data (150-500 km) from Martian years 32-38 (2015-2024) during solar quiet-time. This study investigated the behavior of topside ionosphere (e-, CO2+, O2+, NO+, OH+, O+, N+ \& C+) across different phases of SC over the northern hemisphere. A significant variation in ionosphere is observed over low-latitude (0-30{\deg}N) with higher densities compared to mid-latitude (31-60{\deg}N) across SC. Additionally, we found that the Martian northern ionospheric densities were highest during solar maximum phase on both dayside and nightside compared to low active phases. The dayside densities were approximately 1-2 orders higher compared to those on the nightside. The electron and molecular ions densities increased by factors of 1-5 and 1-13, respectively. While O+ ion density was enhanced by nearly 2-2.5 times, along with an upliftment of 40-50 km in the peak height. The enhanced dayside densities are attributed to the elevated solar irradiance (1.4-2 times) and varying solar wind flux. Furthermore, the enhanced day-to-night plasma transport and elevated solar electron flux during maxima, higher by 33-66\% than during low-activity, can contribute to the increased nightside ionization. This work, for the first time, uses long-term MAVEN datasets across the descending-to-maxima phases of SC to reveal climatology of Martian topside ionosphere.

Figures

Figures reproduced from arXiv: 2507.02368 by the authors.

Figure 7
Figure 7. Time series variations of averaged solar EUV flux (Top panel; left y-axis) and upstream solar wind dynamic pressure (SWDP (nPa)), resultant IMF (|B| (nT)), and electron energy flux (100-500 eV) (Second to Fourth Panels, left y-axis) over different phases of Solar Cycles 24 and 25 in 2015-2024. Similarly, ionospheric monthly averaged electron (green diamonds) and ion density (purple dots) variations (>300 km altitude… view at source ↗

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Works this paper leans on

3 extracted references · 3 canonical work pages

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Reviewed August 6, 2026 · model on record in the stance chip above.