A Unified Climatology of Mars’ Atmospheric Thermal Structure and Variability from MAVEN and TGO Observations

Introduction and Goal

The upper atmosphere of Mars, spanning the mesosphere (60–120 km) and the thermosphere up to the exobase (180–230 km), remains one of the least characterized regions of the planet [1]. Its structure is shaped by solar forcing, upward‑propagating waves, and dust‑driven variability originating in the lower atmosphere; however, the relative importance of these processes and their vertical coupling are not yet fully understood [2]. Two recent missions provide complementary datasets: NASA’s MAVEN mission, operational since 2014, focuses on upper‑atmosphere processes and atmospheric escape, while ESA–Roscosmos’ Trace Gas Orbiter (TGO), in routine operation since 2018, carries the NOMAD and ACS instruments, which retrieve atmospheric profiles from near‑surface layers to the upper thermosphere.

In this work, we combine MAVEN and TGO observations with the primary objective of producing a comprehensive climatology of the thermal structure of the Martian upper atmosphere. This study is part of a broader andn recent project funded by the International Space Science Institute (ISSI) entitled “A multi-mission approach to close the gaps in understanding of the structure and variability in the Mars upper atmosphere”. Most TGO datasets concentrate below 100 km, whereas MAVEN primarily samples thermospheric altitudes. Because TGO data extend to lower altitudes, we actually present results spanning from the troposphere to the exosphere. The combined dataset integrates nine types of measurements from both missions, including in situ observations (NGIMS/MAVEN) and remote‑sensing measurements from NOMAD, ACS, EUVM, and IUVS (solar and stellar occultations, as well as dayglow). Together, these datasets cover multiple Martian years and an altitude range of 30–180 km, providing unprecedented vertical and temporal coverage. Exploiting this complementarity, particularly the vertical coupling between the lower and upper atmosphere, is also a major scientific goal of the present research.

In this climatological study, we explicitly exclude a set of short‑lived and sporadic phenomena, such as dust storms, solar eruptions, and small‑scale atmospheric waves. Our focus is on the systematic variations associated with the following geophysical variables: altitude, latitude, season, local time, solar cycle, and longitude.

Datasets, Synergies, and Challenges

The datasets exhibit highly diverse characteristics, including field of view, spatial and temporal coverage, sensitivity, and noise levels, posing challenges for the synergetic analysis pursued here. To address coverage differences, we devoted substantial effort to designing appropriate binning strategies and averages across geophysical variables. Regarding sensitivity and retrieval performance, we used nominal uncertainties but filtered out the highest‑uncertainty percentile, and we developed a unified quality‑control framework applied to the nominal errors of each experiment. This framework aims to eliminate spurious values and identify potential biases, as revealed through cross‑comparisons within well‑defined geophysical bins. We also performed a variance‑partitioning analysis as a function of geophysical forcings, enabling us to distinguish intrinsic atmospheric variability from instrumental effects. Two vertical coordinates were used: altitude above the Martian aeroid and a modified‑CO₂ scale‑height coordinate, which is more suitable for upper‑atmosphere comparisons. Special attention was given to solar‑occultation datasets from both MAVEN and TGO (terminator measurements at dawn and dusk) owing to their synergistic local‑time coverage and excellent vertical resolution.

Selected Results

We will present a representative sample of this extensive analyses across this broad parameter space, including global composite temperature profiles, deviations from mean distributions, multi‑year time series, and an assessment of the dominant sources of thermal variability. Our results reveal substantial atmospheric variability, highly non‑linear with respect to geophysical parameters, and a hierarchy of dominant processes that varies with altitude and which shapes the global thermal structure.

In particular we found that thermospheric temperatures respond strongly to solar flux, with variations exceeding 50 K above 150 km and decreasing toward 100 km, being very small below this altitude. In contrast, mesospheric temperatures are dominated by global circulation, producing seasonal and latitudinal gradients of 20–40 K. We will show how the combined datasets also reveal interhemispheric asymmetries, the impact of dust storms at multiple altitudes, and the propagation of atmospheric waves.

Comparisons with MarsPCM and MCD simulations demonstrate that the model reproduces very well the mean vertical structure as well the seasonal and latitudinal variations observed, but underestimates the variability by factors of 1.5–2 and exhibit a few biases in the mesopause and upper thermosphere. In particular, tidal amplitudes in the mesosphere are weaker in the models, the lower‑thermosphere thermal gradient occurs at lower altitudes than what is observed, and the coldest thermospheric temperatures predicted by the models are significantly colder than those reported by EUVM.

The resulting MAVEN–TGO climatology provides a robust reference for future measurements, model validation, and studies of Martian atmospheric dynamics and evolution.

 

References

[1] Bougher et al., JGR-Planets, 2017 [2] López-Valverde et al., Space Sci. Rev., 2018 [3] Giuranna et al., Space Sci. Rev., 2025 [4] Heavens et al., Nature, 2018 [5] Yiğit et al., Nature Geoscience, 2023 [6] Jakosky et al., Science, 2015 [7] Korablev et al., Space Sci. Rev., 2018 [8] Vandaele et al., Space Sci. Rev., 2018