We report the gravity wave (GW) statistics accumulated over two Martian years from the second half of Martian Year 34 (MY34) to the middle of MY36 (May 2018 - February 2022). The observations were performed by the middle- and near-infrared (MIR and NIR, respectively) spectrometers of Atmospheric Chemistry Suite (ACS) on board ExoMars Trace Gas Orbiter (TGO). Temperature profiles obtained independently of both channels during simultaneous measurements show a good agreement, thus providing verification and additional confidence in the data. GW parameters such as temperature fluctuations, potential energy per unit mass, and wave drag are retrieved at altitudes up to 160 km from the MIR channel and up to 100 km from the NIR channel. We present seasonal, intraday and latitude distributions of the wave potential energy and drag, serving to represent the wave activity and impact on the dynamics. A comparison of data obtained during the global dust storm (GDS) of MY34 with the corresponding period of MY35 without a storm reveals a reduction of GW activity in mid-latitudes in agreement with previous observations, and enhancement in the polar regions of both hemispheres, which was predicted by theoretical studies using simulations with a high-resolution circulation model. Seasonal variations of the derived GW activity can be linked to changes in the solar tide.

Detecting trace gases such as hydrogen chloride (HCl) in Mars' atmosphere is among the primary objectives of the ExoMars Trace Gas Orbiter (TGO) mission. Terrestrially, HCl is closely associated with active volcanic activity, so its detection on Mars was expected to point to some form of active magmatism/outgassing. However, after its discovery using the mid-infrared channel of the TGO Atmospheric Chemistry Suite (ACS MIR), a clear seasonality was observed, beginning with a sudden increase in HCl

SPICAM-IR, an AOTF spectrometer onboard Mars Express spacecraft with a resolving power of 2,000 covering the spectral range 1-1.7 μm has been observing Mars since 2004. In this wavelength range, it is possible to distinguish between CO2 and H2O ices and measure their band depths. We obtained about 200,000 high-fidelity spectra of CO2 ice in different seasons and locations over the Martian polar caps. The spectra have been associated with slab ice, fine-grained ice, permanent caps, and dark and dirty ice at the cryptic region of the south polar cap. Also, we observed more than 200,000 water ice spectra, specifically its broad feature around 1.5 μm. Water ice is present at the surface or in the atmosphere resulting in a variety of different band depths, often in combination with the CO2 ice. We mapped the equivalent width of 1.43 μm CO2 ice band and the depth of 1.5 μm water ice band, which are the proxies for grain size, and followed their seasonal evolution. From the maps, we produced the edge (outer crocus line) of the CO2 south and north caps for nine Martian Years. The cap edges evolve similarly through all years and are in good agreement with previous OMEGA/Mars Express observations. We also discuss the impact of the global dust storms on the cap edges. Lastly, we interpret some of the water ice observations as water ice clouds in the aphelion cloud belt and the polar hoods.

With the utilization of a novel synergistic approach, we constrain the vertical distribution of water vapor on Mars with measurements from nadir-pointing instruments. Water vapor column abundances were retrieved simultaneously with PFS (sensing the thermal infrared range) and SPICAM (sensing the near-infrared range) on Mars Express, yielding distinct yet complementary sensitivity to different parts of the atmospheric column. We show that by exploiting a spectral synergy retrieval approach, we obtain more accurate water vapor column abundances compared to when only one instrument is used, providing a new and highly robust reference climatology from Mars Express. We present a composite global dataset covering all seasons and latitudes, assembled from co-located observations sampled from seven Martian years. The synergy also offers a way to study the vertical partitioning of water, which has remained out of the scope of nadir observations made by single instruments covering a single spectral interval. Special attention is given to the north polar region, with extra focus on the sublimation of the seasonal polar cap during the late spring and summer seasons. Column abundances from the Mars Climate Database were found to be significantly higher than synergistically retrieved values, especially in the summer Northern Hemisphere. Deviances between synergy and model in both magnitude and meridional variation of the vertical confinement were also discovered, suggesting that certain aspects of the transport and dynamics of water vapor are not fully captured by current models.

We present the first water vapor profiles encompassing the upper mesosphere of Mars, 100–120 km, far exceeding the maximum altitudes where remote sensing has been able to observe water to date. Our results are based on solar occultation measurements by Atmospheric Chemistry Suite (ACS) onboard the ExoMars Trace Gas Orbiter (TGO). The observed wavelength range around 2.7 μm possesses strong CO2 and H2O absorption lines allowing sensitive temperature and density retrievals. We report a maximum H2O mixing ratio varying from 10 to 50 ppmv at 100–120 km during the global dust storm (GDS) of Martian Year (MY) 34 and around southern summer solstice of MY 34 and 35. During other seasons water remains persistently below ~2 ppmv. We claim that contributions of the MY34 GDS and perihelion periods into the projected hydrogen escape from Mars are nearly equivalent.

The paper presents observations of gravity wave-induced temperature disturbances in the Martian atmosphere obtained with the mid-infrared (MIR) spectrometer, a channel of the Atmospheric Chemistry Suite instrument on board the Trace Gas Orbiter (ACS/TGO). Solar occultation measurements of a CO2 absorption band at 2.7 μm were used for retrieving density and temperature profiles between heights of 20 and 160 km with vertical resolution sufficient for deriving small-scale structures associated with gravity waves. Several techniques for distinguishing disturbances from the background temperature have been explored and compared. Instantaneous temperature profiles, amplitudes of wave packets and potential energy have been determined. Horizontal momentum fluxes and associated wave drag have been estimated. The analyzed data set of 144 profiles encompasses the measurements made over the second half of Martian Year 34, from the Solar longitude 165◦ through 355◦. We observe enhanced gravity wave dissipation/breaking in the mesopause region of 100-130 km. Our analysis shows no direct correlation between the wave amplitude and Brunt-Vaisala frequency. It may indicate that convective instability may not be the main mechanism limiting gravity wave growth in the middle atmosphere of Mars.

Temperature and density in the upper Martian atmosphere, above ~100 km, are key diagnostic parameters to study processes of the species’ escape, investigate the impact of solar activity, model the atmospheric circulation, and plan spacecraft descent or aerobraking maneuvers. In this paper, we report vertical profiling of carbon dioxide (CO2) density and temperature from the Atmospheric Chemistry Suite (ACS) solar occultations onboard the ExoMars Trace Gas Orbiter (TGO). A strong CO2 absorption band near 2.7 μm observed by the middle infrared spectrometric channel (ACS MIR) allows the retrieval of the atmospheric thermal structure in a large altitude range, from 20 to 180 km. We present the latitudinal and seasonal climatology of the thermal structure for 1.5 Martian years (MYs), from the middle of MY 34 to the end of MY 35. The results show the variability of distinct atmospheric layers, such as a mesopause (derived from 70 to 150 km) and homopause, changing from 80-90 km at aphelion to 100-110 km at perihelion. Some short-term homopause fluctuations are also observed depending on the dust activity.

The upper atmosphere of Mars is directly affected by solar activity and the resulting solar irradiance impinging upon it. Variations in solar forcing can affect the rate at which atmospheric species escape from the planetary system. Remotely sensed observations of the upper atmosphere of Mars have been made during solar activity extrema of Solar Cycles 22 and 24. These observations were made of D and H Lyman-a emissions using the Mars Atmosphere and Volatile Evolution (MAVEN) mission and the Hubble Space Telescope (HST) high resolution spectrographs. Data obtained from the two missions are analyzed and used to derive densities and escape rates of D and H from the martian upper atmosphere. The results show that the properties of these two water-spawned atoms vary with solar cycle, and display significant inter-annual variability, mainly due to variations in atmospheric temperature. The findings suggest that cooler atmospheric temperatures due to reduced solar EUV flux may enhance the abundance of H atoms in the upper atmosphere of Mars, yet this does not increase their escape rates.

Observations by several cameras on the Perseverance rover showed a 22° scattering halo around the Sun over several hours on the morning of sol 292 (15 December 2021). Such a halo has not previously been seen off Earth. The halo occurred during the aphelion cloud belt season and the cloudiest time yet observed from the Perseverance site. The halo required crystalline water-ice cloud particles in the form of hexagonal columns large enough for refraction to be significant, at least 11 µm in diameter and length. Near 44 km altitude, fall speeds would have been 0.3-1 m/s for the smallest allowed particles. Over the 3.3-hour duration of the halo, particles could have fallen 3-12 km, causing downward transport of water and dust. Halo-forming clouds are likely rare due to the high supersaturation of water that is required but may be more common in northern subtropical regions during mid-northern summer.

The Perseverance rover, Mars 2020 mission, landed on the surface of the Jezero Crater, on February, 18th 2021. This Martian crater is suspected to have hosted a paleolake as evidenced by the numerous detections of aqueously-altered phases and thus is a promising candidate for the search for past Martian life. The SuperCam instrument, elaborated by a consortium of American and European laboratories, plays a leading role in this investigation thanks to its highly versatile payload providing rapid, synergistic, fine-scale mineralogy, chemistry, and color imaging. After its landing, the first measurements of Martian targets with the infrared spectrometer of SuperCam (IRS) showed new instrumental behaviors that had to be characterized and calibrated to derive unbiased science data. The IRS radiometric response has thus been calibrated using periodic observations of the Aluwhite SuperCam Calibration Target (SCCT). Parasitic effects were understood and mitigated, and the instrumental dark and noise are characterized and modeled. The reflectance calibrated data products, provided periodically on the NASA Planetary Data System, are corrected from the main instrumental features.

On Mars, saturation is the major factor constraining the vertical distribution of water vapor. Recent measurements of water and temperature profiles showed that water can be strongly supersaturated at and above the level where clouds form during aphelion and perihelion seasons. Since 2018, the near-infrared spectrometer (NIR) of the Atmospheric Chemistry Suite onboard the Trace Gas Orbiter has measured H2O and temperature profiles using solar occultation in the infrared from below 10 km to 100 km of altitude. Here we provide the first long-term monitoring of the water saturation state. The survey spans 2 Martian years from Ls=163° of MY34 to the Ls=180° of MY36. We found that water is often supersaturated above aerosol layers. In the aphelion season, water mixing ratio above 40 km in the mid-to-high latitudes was below 3 ppmv and yet is found to be supersaturated. Around perihelion, water is also supersaturated above 60 km with a mixing ratio of 30-50 ppmv. Stronger saturation is observed during the dusty season in MY35 compared to what was observed in MY34 during the Global Dust Storm and around perihelion. Saturation varied between evening and morning terminators in response to temperature modulation imparted by thermal tides. Although water vapor is more abundant in the evening, colder morning temperatures induce a daily peak of saturation. This dataset establishes a new paradigm for water vapor on Mars, revealing that supersaturation is nearly ubiquitous, particularly during the dust season, thereby promoting water escape on an annual average.

We assimilate atmospheric temperature profiles and column dust optical depth observations from the ExoMars Trace Gas Orbiter Atmospheric Chemistry Suite thermal infrared channel (TIRVIM) into the LMD Mars Global Climate Model. The assimilation period is Mars Year 34 Ls = 182.3 - 211.4, covering the onset and peak of the 2018 global dust storm. We assimilated observations using the Local Ensemble Transform Kalman Filter with 36 ensemble members and adaptive inflation; our nominal configuration assimilated TIRVIM temperature profiles to update temperature and dust profiles, followed by dust column optical depths to update the total column dust abundance. The observation operator for temperature used the averaging kernels and prior profile from the TIRVIM retrievals. We verified our analyses against in-sample TIRVIM observations and independent Mars Climate Sounder (MCS) temperature and dust density-scaled opacity profiles. When dust observations were assimilated, the root-mean-square temperature error verified against MCS fell by 50% during the onset period of the storm, compared with assimilating temperature alone. At the peak of the storm the analysis reproduced the location and magnitude of the peak in the nighttime MCS dust distribution, along with the surface pressure diurnal cycle measured by Curiosity with a bias of less than 10 Pa. The analysis winds showed that, at the peak of the storm, the meridional circulation strengthened, a 125 m/s asymmetry developed in the midlatitude zonal jets, the diurnal tide weakened near the equator and strengthened to 10-15 K at midlatitudes, and the semi-diurnal tide strengthened almost everywhere, particularly in the equatorial lower atmosphere.