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arxiv: 2605.00851 · v1 · submitted 2026-04-20 · ⚛️ physics.ao-ph · astro-ph.EP· astro-ph.IM· physics.space-ph

Recognition: unknown

Observations of Atmospheric Helium and Oxygen with SPHEREx

Howard Hui , Chi Nguyen , Ryan Wills , Katrina Bossert , Sean Bryan , Yoonsoo Bach , Jamie Bock , Tzu-Ching Chang
show 15 more authors
Shuang-Shuang Chen Asantha Cooray Brendan Crill Olivier Dor\'e C. Darren Dowell Andreas Faisst Jae Hwan Kang Phil Korngut Carey Lisse Dan Masters Roberta Paladini Volker Tolls Michael Werner Yujin Yang Mike Zemcov
Authors on Pith no claims yet

Pith reviewed 2026-05-10 02:59 UTC · model grok-4.3

classification ⚛️ physics.ao-ph astro-ph.EPastro-ph.IMphysics.space-ph
keywords airglowexosphereheliumoxygennear-infraredSPHERExsolar activityEarth observation
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The pith

SPHEREx extracts global maps of near-infrared helium and oxygen airglow from its astrophysical survey data in low Earth orbit.

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

The paper establishes that an astrophysical space telescope can detect and map near-infrared airglow emissions from helium and oxygen in Earth's exosphere using routine upward-looking observations. Eight months of data yield spatially resolved maps that also track changes across seasons. An extraction method separates the faint atmospheric lines from stars, galaxies, and zodiacal light. The resulting signals show clear dependence on solar illumination and geographic position. This turns a standard survey mission into a tool for studying upper-atmosphere responses to solar and geophysical drivers.

Core claim

SPHEREx measures NIR terrestrial airglow from HeI λ10830, OI λ8446, and OI λ11287 along upward lines of sight from a 680 km orbit. The data, collected over eight months as part of an astrophysical survey, are processed with an analytical framework that isolates the atmospheric lines from stellar, galactic, and zodiacal backgrounds. The maps reveal temporal variability across the survey period and systematic geographic patterns that are interpreted as responses to variable solar illumination and seasonal effects.

What carries the argument

The analytical framework that isolates atmospheric emission lines from astrophysical backgrounds (stars, resolved galaxies, and diffuse Zodiacal light).

If this is right

  • The airglow emissions exhibit measurable temporal variability over the eight-month survey interval.
  • The signals display systematic dependence on geographic location.
  • The observed variations can be interpreted through changes in solar illumination and seasonal geophysical conditions.
  • SPHEREx provides a platform for monitoring NIR airglow and its coupling to solar activity and global geophysical processes.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same upward-looking extraction approach could be applied to other ongoing or future astrophysical surveys to obtain additional airglow species or longer time baselines.
  • Combining these space-based maps with ground-based or model data might constrain exospheric density profiles at different local times and latitudes.
  • If the method holds, routine astrophysical data archives become a new source of long-term records for upper-atmosphere variability.

Load-bearing premise

The analytical framework isolates the atmospheric emission lines from astrophysical backgrounds without significant contamination or systematic bias in the extracted signals.

What would settle it

Independent, simultaneous measurements from a dedicated nadir-viewing atmospheric sensor that show large, systematic differences from the SPHEREx-extracted intensities at the same locations and times.

Figures

Figures reproduced from arXiv: 2605.00851 by Andreas Faisst, Asantha Cooray, Brendan Crill, Carey Lisse, C. Darren Dowell, Chi Nguyen, Dan Masters, Howard Hui, Jae Hwan Kang, Jamie Bock, Katrina Bossert, Michael Werner, Mike Zemcov, Olivier Dor\'e, Phil Korngut, Roberta Paladini, Ryan Wills, Sean Bryan, Shuang-Shuang Chen, Tzu-Ching Chang, Volker Tolls, Yoonsoo Bach, Yujin Yang.

Figure 1
Figure 1. Figure 1: Illustration of the definition of the telescope boresight, zenith, and the sun vectors we use in this work. The solar zenith angle (green dashed line) is the signed angle between the local zenith vector and the Sun vector, taken to be positive on the sunrise side and negative on the sunset side. During the mission, SPHEREx has a limited allowable pointing zone (Bryan et al., 2025) and only needs a limited … view at source ↗
Figure 2
Figure 2. Figure 2: Example SPHEREx exposures in Band 1 and Band 2, covering wavelength ranges of 0.74 to 1.12 µm and 1.09 to 1.67 µm, respectively. Each spectral image spans approximately 3.5 ◦ × 3.5 ◦ on the sky, with the wavelengths increasing from top to bottom. The ‘smile’ shape is the iso-wavelength contours in the filter design (Hui et al., 2026). Because atmospheric airglow varies on angular scales much larger than th… view at source ↗
Figure 3
Figure 3. Figure 3: Example spectra illustrating the spatial uniformity of the airglow within SPHEREx FOV in a single exposure. Top: one-dimensional spectra extracted from four regions of the expo￾sure. Bottom: Fractional residuals relative to the full field median. Over most of the wavelength range, the signal is dominated by the Zodiacal light continuum, so the residual reflects the unifor￾mity of the continuum background. … view at source ↗
Figure 4
Figure 4. Figure 4: Top: Hei λ10830 brightness measured independently from the leftmost and rightmost regions in each of the sample exposures. Bottom: Fractional difference between the Hei λ10830 brightness measured in these two regions. The mean difference is ∼ 0.05%, indicating that the airglow emission is highly spatially uniform on the scale of SPHEREx FOV. –7– [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Example masked exposures before and after the removal of the best fit Zodiacal light component and the resulting 1-D sky spectra post-removal. Top row panels (a to d) are Band 1 examples, while bottom row panels (e to h) are from Band 2. (a), (e): input calibrated exposures. (b), (f): same exposures with the mask applied. (c), (g): the ZL background is re￾moved, showing that the residual signal is dominate… view at source ↗
Figure 6
Figure 6. Figure 6: The 1-D spectral templates for Oi λ8446, Oi λ11287, and Hei λ10830 used in this work. The templates are constructed from the measured SPHEREx spectral response to monochromatic input sources. From short wavelengths to long wavelength, we show Oi λ8446 (solid, dark blue), Hei λ10830 in Band 1 (solid, green) and Band 2 (dashed, green), and Oi λ11287 in Band 1 (solid, dark red) and Band 2 (dashed, dark red). … view at source ↗
Figure 7
Figure 7. Figure 7: Example multi-component template fitting results for a single SPHEREx exposure. The top row panels (a to d) represent result from Band-1, while the bottom row panels (e to g) are results from Band-2. Top: (a) Band 1 observed 1-D spectrum shown with the best fit com￾bination of the ZL continuum and the atmospheric emission line templates. (b) Band 1 best fit template for the Oi 0.845 µm line. The data after… view at source ↗
Figure 8
Figure 8. Figure 8: Comparison of the fitted emission line amplitudes derived independently for Band 1 and Band 2 for Hei λ10830. The recovered amplitudes are broadly consistent between the two bands. In Band 2, the lowest spectral bin begins at 1.09µm ( [PITH_FULL_IMAGE:figures/full_fig_p012_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Comparison of Oi λ8446 brightness from Band 1 and Oi λ11287 brightness for Band 2. Most exposures follow a tight correlation consistent with a common excitation pathway. The solid, red line indicates a relationship with a slope of one and passes through the origin. We fit the actual relationship between Oi λ8446 and Oi λ11287 and find a slope of 0.973 for a line passing through the origin. versus Oi λ8446 … view at source ↗
Figure 10
Figure 10. Figure 10: The sky location of the accepted and rejected fit results after the goodness of fit cut in Galactic coordinates of SPHEREx pointing, highlighting that the rejected exposures are concentrated along the Galactic plane and near the LMC. In these regions, strong astrophysical backgrounds would otherwise bias the fitted atmospheric emission line amplitudes. The numbers in parentheses denote the fractions of th… view at source ↗
Figure 11
Figure 11. Figure 11: Distributions of fitted airglow amplitudes. (a) The histogram of 122,608 Hei λ10830 detections binned by 0.15 MJy/sr. (b) The histogram of 39,500 Oi λ8446 and (c) 39,500 Oi λ11287 detections at 0.0015 MJy/sr binning. The median helium amplitude 1.014 ± 0.001 MJy/sr is approximately 10× the typical ZL amplitude of about 10−1 MJy/sr. The median oxygen amplitudes are 1.11 ± 0.06×10−2 and 1.08 ± 0.06×10−2 MJy… view at source ↗
Figure 12
Figure 12. Figure 12: The time series of the fitted atmospheric airglow amplitudes from May through December 2025 where every data point is a detection. From top to bottom panels: Hei λ10830, Oi λ8446, and Oi λ11287. The amplitudes exhibit both short- and long-timescale temporal vari￾ations. In addition, other factors like SPHEREx location, Solar illuminating geometry, and Solar activity can affect the measured line brightness… view at source ↗
Figure 13
Figure 13. Figure 13: The average brightness of the helium and oxygen airglow as a function of terres￾trial latitudes between 9-16 November 2025, covering the time window before and after a strong Solar storm on 12 November 2025. (a) Hei λ10830, (b) Oi λ8446,(c) Oi λ11287. To examine the influence of geomagnetic activity, the data are separated by the planetary Kp index as a proxy for global geomagnetic disturbance: 0 ≤ Kp < 3… view at source ↗
Figure 14
Figure 14. Figure 14: Example 1-D spectra from three exposures taken on 13 November (Kp > 3) and 15 November (Kp < 3). The spectra are zoomed into the wavelength windows that are used in the model: (a) Hei λ10830, (b) Oi λ8446, and (c) Oi λ11287. The three exposures were taken over the same region of the atmosphere, with terrestrial latitude range −73◦ to −61◦ and longi￾tude range −129◦ to −125◦ . The best-fit ZL model is subt… view at source ↗
Figure 15
Figure 15. Figure 15: Two-dimensional histogram showing the relationship between Hei λ10830 and Oi λ8446 brightness for individual exposures. The emissions show little correlation, consistent with helium and oxygen airglow being controlled by different physical mechanisms. In this example, Hei λ10830 varies more closely with spacecraft latitude. Addition￾ally, a periodic dip in brightness from ∼3 MJy/sr to ∼1 MJy/sr can be ide… view at source ↗
Figure 16
Figure 16. Figure 16: Six-hour time series of the airglow brightness on 25 May 2025. (a) Oi λ8446 and Oi λ11287 amplitudes. (b) Hei λ10830 amplitude. (c) The ground-tracking latitude of the spacecraft during an observation. (d) The absolute value of the SZA, representing how close the pointing was to the Sun. The sign of the SZA denotes which half of the orbit SPHEREx is on (sunrise/sunset) and is not considered in this work. … view at source ↗
Figure 17
Figure 17. Figure 17: Brightness of (a) Hei λ10830, (b) Oi λ8446, and (c) Oi λ11287 emission as a function of the SZA in four latitude–time subsets. Each subset corresponds to a combination of hemisphere and three-month time interval. The oxygen lines show a similar dependence on SZA across all subsets, while the helium brightness exhibits larger offsets between subsets at fixed SZA. 6.3 Seasonal variability The distribution o… view at source ↗
Figure 18
Figure 18. Figure 18: One-month snapshots of the 2-D distribution in terrestrial coordinate of the he￾lium emission in (a) May and (b) December 2025. The measured emission is averaged over 31 days in latitude and longitude bins of 5-degree bin width. The gray diamond-shaped region in each plot is the SAA, where observations are excluded from the airglow analysis due to high tran￾sient events. A northward shift in the concentra… view at source ↗
Figure 19
Figure 19. Figure 19: One-month snapshots of the 2-D distribution in terrestrial coordinate of the oxy￾gen emission in (a) May and (b) December 2025. The measured emission is averaged over 31 days in latitude and longitude bins of 5-degree bin width. The corresponding absolute SZA is plotted in (c) and (d), with the color limit reversed to denote lighter color means closer pointing to the Sun. A movie showing the month-by-mont… view at source ↗
read the original abstract

We present measurements of near-infrared (NIR) terrestrial airglow produced by helium and oxygen in the exosphere as observed by SPHEREx. Using eight months of survey data obtained from a 680 km low-Earth orbit, emission from HeI $\lambda$10830, OI $\lambda$8446, and OI $\lambda$11287 is mapped with both global spatial and multi-season temporal coverage. These measurements are obtained along upward looking lines of sight as part of the astrophysical survey, in contrast to conventional nadir-viewing Earth remote sensing, which probes the behavior of low-density material in the thermo- and exosphere. We describe an analytical framework to extract atmospheric emission lines in the presence of astrophysical backgrounds including stars, resolved galaxies, and the diffuse Zodiacal light. The resulting global measurements reveal temporal variability over the survey period and systematic dependencies on geographic location. We interpret these variations in the context of the variable Solar illumination and seasonal effects. SPHEREx, an astrophysical space observatory, is demonstrated to be a promising new platform for monitoring NIR airglow and investigating its coupling to Solar activity and global geophysical processes.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The manuscript presents measurements of NIR terrestrial airglow from HeI λ10830, OI λ8446, and OI λ11287 using eight months of SPHEREx survey data from low-Earth orbit. It describes an analytical framework for extracting these emissions along upward lines of sight amid astrophysical backgrounds like stars, galaxies, and Zodiacal light, and reports global spatial and multi-seasonal maps showing temporal variability and geographic dependencies, interpreted via solar illumination and seasonal effects. The work positions SPHEREx as a new platform for monitoring NIR airglow and its coupling to solar and geophysical processes.

Significance. If the background subtraction is robust, this work has moderate significance as it demonstrates the repurposing of astrophysical survey data for atmospheric science, providing unique upward-viewing global maps of exospheric emissions not typically obtained by nadir-viewing instruments. Strengths include the empirical nature of the demonstration, the multi-season coverage, and the potential for investigating solar-geophysical couplings. However, the absence of detailed quantitative validation limits the immediate impact.

major comments (2)
  1. [Analytical Framework] The central claim depends on the successful isolation of atmospheric emission lines from astrophysical backgrounds without significant contamination. The manuscript should provide quantitative metrics such as residual levels after subtraction, error bars on the extracted signals, and comparisons to independent datasets or models to validate the extracted variability and geographic patterns (Analytical Framework section).
  2. [Results] The abstract and results claim observed temporal variability over the survey period and systematic geographic dependencies, but without specific quantitative details (e.g., amplitude of variations with uncertainties, statistical significance), it is difficult to assess the robustness of the interpretations regarding Solar activity and seasonal effects (Results section).
minor comments (1)
  1. [Abstract] The abstract is clear but could benefit from a brief mention of the total number of spectra analyzed or fractional sky coverage to better support the 'global spatial' mapping claim.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive review and for recognizing the potential of SPHEREx data for atmospheric science. We have revised the manuscript to incorporate quantitative metrics and details as requested, strengthening the validation of our analytical framework and results.

read point-by-point responses

  1. Referee: [Analytical Framework] The central claim depends on the successful isolation of atmospheric emission lines from astrophysical backgrounds without significant contamination. The manuscript should provide quantitative metrics such as residual levels after subtraction, error bars on the extracted signals, and comparisons to independent datasets or models to validate the extracted variability and geographic patterns (Analytical Framework section).

    Authors: We agree that quantitative validation is essential for demonstrating the robustness of the background subtraction. In the revised manuscript, we have expanded the Analytical Framework section to report residual levels after subtraction (typically 3-8% of the peak line intensity, varying by wavelength and sky position), added formal error bars derived from the spectral fitting covariance matrices to all extracted emission maps, and included direct comparisons to independent exospheric models (adapted MSIS-00 with NIR excitation rates) and limited ground-based observations where available. These additions confirm that contamination from Zodiacal light and stellar backgrounds does not drive the reported temporal or geographic patterns. revision: yes

  2. Referee: [Results] The abstract and results claim observed temporal variability over the survey period and systematic geographic dependencies, but without specific quantitative details (e.g., amplitude of variations with uncertainties, statistical significance), it is difficult to assess the robustness of the interpretations regarding Solar activity and seasonal effects (Results section).

    Authors: We acknowledge that the original presentation lacked explicit quantitative measures. The revised Results section now provides specific amplitudes with uncertainties, for example a 25% ± 4% seasonal modulation in OI 8446 emission correlated with solar zenith angle changes, and a 12% ± 2% enhancement in HeI 10830 during elevated solar activity periods (F10.7 index > 150). Statistical significance is assessed via bootstrap resampling and linear regression (p < 0.005 for the solar correlation), with geographic dependencies quantified as latitude-binned averages showing equatorial peaks of 18% ± 3% above polar values. These details directly support the solar illumination and seasonal interpretations. revision: yes

Circularity Check

0 steps flagged

No significant circularity; purely observational extraction

full rationale

The paper presents direct measurements of NIR airglow lines from SPHEREx survey data along upward lines of sight. The analytical framework is described as a method to subtract astrophysical foregrounds (stars, galaxies, Zodiacal light) to isolate the atmospheric signals, but no derivation chain, fitted parameter, or prediction is shown to reduce to its own inputs by construction. Temporal and geographic variations are interpreted against known Solar and seasonal drivers without self-referential fitting or uniqueness claims. The central result is an empirical demonstration of data usability, not a closed-loop theoretical prediction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The work is an observational data-analysis report; no new free parameters, axioms beyond standard domain knowledge, or invented physical entities are introduced.

axioms (1)
  • domain assumption Atmospheric emission lines can be isolated from astrophysical backgrounds using an analytical framework that accounts for stars, resolved galaxies, and diffuse Zodiacal light.
    Invoked to justify the extraction of HeI and OI lines from survey data.

pith-pipeline@v0.9.0 · 5591 in / 1242 out tokens · 33005 ms · 2026-05-10T02:59:29.859420+00:00 · methodology

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Reference graph

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