1,1,1,1,1,2,3,4,5,- 1Royal Belgian Institute for Space Aeronomy, Planetary Aeronomy, Uccle, Belgium (loic.trompet@aeronomie.be)
- 2Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Japan
- 3Department of Geophysics, Graduate School of Science, Tohoku University, Sendai, Japan
- 4Instituto de Astrofìsica de Andalucía, Consejo Superior de Investigaciones Científicas (CSIC), Granada, Spain
- 5School of Physical Sciences, The Open University, Milton Keynes, UK
- 6Istituto de Astrofisica e Planetologia Spaziali, INAF, Rome, Italy
The SO channel of the NOMAD instrument on board ESA’s Trace Gas Orbiter (TGO) has a spectral range extending from 2.2 to 4.2 µm (2400 cm-1 to 4600 cm-1). By solar occultation, the intense ν1+ν3 band of CO2 (around 2.7 µm or 3710 cm-1) is suitable for deriving CO2 density and temperature in the upper thermosphere of Mars at altitudes around 140 to 190 km. The lower altitude limit is due to the saturation of the CO2 molecular lines in that band. The retrieval algorithm is identical to the one described in Trompet et al. (2023) and relies on the calibration method outlined in Liuzzi et al. (2019), which was further improved in Villanueva et al. (2022). The CO2 density profiles are regularized using a Tikhonov method, and the temperature profiles are derived assuming hydrostatic equilibrium. A total of 5700 profiles were derived from April 21, 2018 (MY 34, LS 163°) to June 30, 2025 (MY 38, LS 104°).
Datasets of the Martian upper thermosphere at the terminator are rather sparse, being limited to observations from the Extreme UV monitor (EUVM - Thiemann et al., 2018) on board NASA’s MAVEN orbiter and the MIR channel of the Atmospheric Chemistry Suite (ACS-Belyaev et al., 2022) also on board TGO, which uses the same CO2 band at 2.7 µm. Despite this limited coverage, some collocated profiles suitable for comparisons are found amongst the datasets of EUVM, ACS-MIR, and NOMAD-SO.
Kumar et al. (2024) already derived characteristics of thermal tides for six sets of EUVM measurements. However, extending those measurements helps to confirm those characteristics and infer further information on thermal tides through comparison with the Mars Climate Database (MCD - Gonzalez-Galindo et al., 2015). The tides simulated by the MCD are in good agreement with those derived from TGO and MAVEN, with a still weaker amplitude likely due to the averaging performed within the MCD dataset. The datasets of both EUVM and NOMAD show the presence of a thermospheric polar warming at aphelion (Thiemann et al., 2024). In addition, the averaged profiles of NOMAD are compared to those of the Venus thermosphere derived from the SOIR instrument (Mahieux et al., 2023).
References:
Belyaev et al. (2022), JGR: Planets, 127 (10), https://doi.org/10.1029/2022JE007286
Gonzalez-Galindo et al. (2015), 120 (11), https://doi.org/10.1002/2015JE004925
Kumar et al. (2024), JGR: Planets, 129 (4), https://doi.org/10.1029/2023JE007887
Liuzzi et al. (2019), Icarus (321), https://doi.org/10.1016/j.icarus.2018.09.021
Mahieux et al. (2023), Icarus, 405, https://doi.org/10.1016/j.icarus.2023.115713
Thiemann et al. (2018), JGR: Planets, 123 (9), https://doi.org/10.1029/ 2018JE005550
Thiemann et al. (2024), GRL, 51 (5), https://doi.org/10.1029/2023GL107140
Trompet et al. (2023), JGR: Planets, 128 (3), https://doi. org/10.1029/2022JE007277
Villanueva et al. (2022), JRL, 49 (12), https://doi. org/10.1029/2022GL098161
How to cite: Trompet, L., Neary, L., Thomas, I., Mahieux, A., Robert, S., Aoki, S., Brines, A., López-Valverde, M. Á., Patel, M., Bellucci, G., and Vandaele, A. C.: CO2 density and temperature derived from NOMAD/TGO in the upper thermosphere of Mars, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18692, https://doi.org/10.5194/egusphere-egu26-18692, 2026.
