Depletion of <sup>13</sup>C in CO in the Atmosphere of Mars Suggested by ExoMars-TGO/NOMAD Observations
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Bibliographic record
Abstract
Abstract The atmosphere of Mars is mainly composed by carbon dioxide (CO 2 ). It has been predicted that photodissociation of CO 2 depletes 13 C in carbon monoxide (CO). We present the carbon 13 C/ 12 C isotopic ratio in CO at 30–50 km altitude from the analysis of the solar occultation measurements taken by the instrument Nadir and Occultation for Mars Discovery on board the ExoMars Trace Gas Orbiter (ExoMars-TGO). We retrieve 12 C 16 O, 13 C 16 O, and 12 C 18 O volume mixing ratios from the spectra taken at 4112–4213 cm −1 , where multiple CO isotope lines with similar intensities are available. The intensities of the 12 C 16 O lines in this spectral range are particularly sensitive to temperature, thus we derive the atmospheric temperature by retrieving CO 2 density with simultaneously measured spectra at 2966–2990 cm −1 . The mean δ 13 C value obtained from the 13 C 16 O/ 12 C 16 O ratios is −263‰, and the standard deviation and standard error of the mean are 132‰ and 4‰, respectively. The relatively large standard deviation is due to the strong temperature dependences in the 12 C 16 O lines. We also examine the 13 C 16 O/ 12 C 18 O ratio, whose lines are less sensitive to temperature. The mean δ value obtained with 12 C 18 O instead of 12 C 16 O is −82‰ with smaller standard deviation, 60‰. These results suggest that CO is depleted in 13 C when compared to CO 2 in the Martian atmosphere as measured by the Curiosity rover. This depletion of 13 C in CO is consistent with the CO 2 photolysis-induced fractionation, which might support a CO-based photochemical origin of organics in Martian sediments.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it