The search for water on Mars has long been a theme of intense exploration, as it represents a means of addressing Mars’ current climate as well as its evolution in the recent and more distant past. Since the 1970s, several missions have carried instruments to track water in the atmosphere, leading to the conceptualization of a water cycle on Mars characterized by intense seasonal variability in water vapor abundance across the planet. After Mariner 9, Viking, Phobos 2 and Mars Global Surveyor, Mars Express has become the fifth orbiter capable of detecting water vapour, with unique features: measurements by several instruments, each probing a distinct wavelength region from near-infrared to thermal infrared, altitude-dependent profiling of water thanks to solar occultation, and observation in the exosphere of its by-product, hydrogen atoms, which can escape into space, depriving Mars of its primordial water reservoir. Thanks to Mars Express, a new vision of Mars’ water cycle and escape processes has emerged. The achievements of Mars Express, as well as the legacy of other missions, which established the foundations of our understanding of Mars’ water cycle are presented in this article.

By the utilisation of a novel synergistic approach, we constrain the vertical distribution of water vapor on Mars with nadir-pointing instruments. Water vapor column abundances were retrieved simultaneously from 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. This approach 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 specific spectral range. Here we present a global dataset covering all seasons and latitudes, with measurements taken over 8 Martian years. Special focus is given to the high-latitude regions in spring and summer during the sublimation of the seasonal polar cap. A significant deviance was discovered between the retrieved vertical distribution water vapor, and the predicted profile from the Mars Climate Database, which is used as prior. We also show that by exploiting a synergistic retrieval approach, we obtain more accurate water vapor column abundances compared to when only one instrument is used. The synergistic retrieval has a tendency to obtain a lower total column abundance compared to the prior, albeit with a stronger vertical partitioning. This indicates a more prominent low-altitude layer, with more water vapor contained close to the surface than predicted by models.

Despite the growing importance of planetary Space Weather forecasting and radiation protection for science and robotic exploration and the need for accurate Space Weather monitoring and predictions, only a limited number of spacecraft have dedicated instrumentation for this purpose. However, every spacecraft (planetary or astronomical) has hundreds of housekeeping sensors distributed across the spacecraft, some of which can be useful to detect radiation hazards produced by solar particle events. In particular, energetic particles that impact detectors and subsystems on a spacecraft can be identified by certain housekeeping sensors, such as the Error Detection and Correction (EDAC) memory counters, and their effects can be assessed. These counters typically have a sudden large increase in a short time in their error counts that generally match the arrival of energetic particles to the spacecraft. We investigate these engineering datasets for scientific purposes and perform a feasibility study of solar energetic particle event detections using EDAC counters from seven European Space Agency Solar System missions: Venus Express, Mars Express, ExoMars-Trace Gas Orbiter, Rosetta, BepiColombo, Solar Orbiter, and Gaia. Six cases studies, in which the same event was observed by different missions at different locations in the inner Solar System are analyzed. The results of this study show how engineering sensors, for example, EDAC counters, can be used to infer information about the solar particle environment at each spacecraft location. Therefore, we demonstrate the potential of the various EDAC to provide a network of solar particle detections at locations where no scientific observations of this kind are available.

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 data set covering all seasons and latitudes, assembled from colocated 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. Deviations 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.

Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Journal of Geophysical Research - Planets. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing an older version [v1]Go to new versionConstraining near-surface water vapor on Mars: a spectral synergy climatological survey applied to PFS and SPICAM nadir observationsAuthorsElise W.KnutseniDFranckMontmessiniDLoïcVerdierGaetanLacombeFranckLefèvreiDStephaneFerroniDMarcoGiurannaPaulinaWolkenbergiDAnna A.FedorovaiDAlexanderTrokhimovskiyOleg IKorableviDSee all authors Elise W. KnutseniDCorresponding Author• Submitting AuthorLATMOSiDhttps://orcid.org/0000-0002-7702-2844view email addressThe email was not providedcopy email addressFranck MontmessiniDLATMOS CNRS/UVSQ/IPSLiDhttps://orcid.org/0000-0002-4187-1457view email addressThe email was not providedcopy email addressLoïc VerdierLATMOS CNRS/UVSQ/IPSLview email addressThe email was not providedcopy email addressGaetan LacombeLATMOS CNRS/UVSQ/IPSLview email addressThe email was not providedcopy email addressFranck LefèvreiDLATMOSiDhttps://orcid.org/0000-0001-5294-5426view email addressThe email was not providedcopy email addressStephane FerroniDACRI-STiDhttps://orcid.org/0000-0002-0631-5674view email addressThe email was not providedcopy email addressMarco GiurannaIstituto di Astrofisica e Planetologia Spazialiview email addressThe email was not providedcopy email addressPaulina WolkenbergiDIstituto Nazionale di Astrofisica, Istituto di Astrofisica e Planetologia SpazialiiDhttps://orcid.org/0000-0001-6769-3719view email addressThe email was not providedcopy email addressAnna A. FedorovaiDSpace Research InstituteiDhttps://orcid.org/0000-0002-4176-2955view email addressThe email was not providedcopy email addressAlexander TrokhimovskiySpace Research Institute (IKI)view email addressThe email was not providedcopy email addressOleg I KorableviDSpace Research Institute (IKI)iDhttps://orcid.org/0000-0003-1115-0656view email addressThe email was not providedcopy email address

Summary The mid-infrared channel of the Atmospheric Chemistry Suite (ACS) [1] onboard ESA’s Trace Gas Orbiter (TGO) has performed a sensitive search of methane in the Martian atmosphere using the solar occultation technique for more than two Mars years (four terrestrial years). The first two reports [2,3] have concluded on the global absence of methane detection above a mean level of 50 then 20 parts-per-trillion-per-volume (pptv), contrasting with the 0.4 to 45 ppbv concentrations reported from Earth-ground-observations, Mars orbiters, and from Mars’ surface by the Curiosity rover [5,6,7,8,9]. Here we present an update of the ACS methane search compiling all the ACS data collected up to summer 2022. Introduction For several decades, methane on Mars has been the subject of a continuous and intense search for it may resonate with an ongoing geophysical or biogenic activity on a planet that has long been perceived as inert. After a succession of failed attempts and positive detections between 2004 and 2019 [4,5,6,7,8,9,21,22], TGO started its trace gas detection mission in April 2018 and has continued since then. With its two separate state-of-the-art infrared spectrometers specifically conceived to achieve outstanding detection performances [1,10] for the ultra-sensitive search of a list of trace gases, including methane, TGO was aimed at confirming the presence of methane at Mars, or alternatively to establish the smallest upper limits possible. The Atmospheric Chemistry Suite (ACS) developed by IKI with the support of CNES is one of the spectrometers of TGO. Together with NOMAD, they offer a complementary access to the entire wavelength range from UV to thermal IR. They are also both observing the mid-IR range and therefore provide a redundant and thus reliable exploration of the presence of a variety of trace gases. Among the greatest achievements of these two experiments, we shall mention the joint observation of HDO and H2O [11,12], the discovery of HCl [13,14,15], the close and joint monitoring of water and ozone [16,17,18], as well as the first CO profiles [19]. Method The mid-infrared range, in particular the region around the fundamental 3.3 μm band of the C-H bond, provides the most sensitive way to detect methane and higher-order hydrocarbons (Fig. 1). With ACS, this spectral region has been explored around Mars during the last four years and has revealed an absence of methane above a limit of 20 pptv (Fig. 2), while NOMAD similarly established such limit to 60 pptv [20]. The technique of solar occultation is known to be more sensitive than nadir since the Sun is a source at Mars that is ~600 000 times brighter that Mars itself. While the ubiquitous atmospheric dust prevents observing the near-surface region, the high-resolving power (30 000) and its high Signal-to-Noise Ratio (~10 000 at low level of dust) compensate for this limitation. We attempt to detect CH4 using the R2 region which features the most intense individual lines of the band system. This region was backed up by parallel search in three other regions to have confirmation in case of a positive detection. Results With two Martian years of survey, the dataset consists of more than 1 000 individual altitude profiles. Since [3], improvements in the data processing have been implemented. This 4-year dataset will be presented along with its implications in regard to other observational studies and model attempts to explain reconcile the various observations. [1] Korablev, O., et al. 2018. Space Sci. Rev. [2] Korablev, O., et al. 2019. Nature [3] Montmessin, F., et al. 2021. Astron. & Astrophys. [4] Lellouch, E., et al. 2000. Astron. & Astrophys. [5] Formisano, V., et al., 2004. Science [6] Krasnopolsky, V. et al., 2004. Icarus [7] Mumma, M. et al., 2009. Science [8] Webster, C.R., et al., 2015, Science [9] Webster, C.R., et al., 2018, Science [10] Vandaele, A.C., et al. 2018. Space Sci. Rev. [11] Villanueva, G. et al., 2020. Sci. Adv. [12] Alday, J. et al., 2021. Nat. Ast. [13] Korablev, O., et al., 2021. Sci. Adv. [14] Aoki, S., et al., 2021. Geophys. Res. Let. [15] Olsen, K. et al., 2021. Astron. & Astrophys. [16] Fedorova et al., A., et al., 2020, Science [17] Patel, M., et al., 2021, J. of Geophys. Res. [18] Belyaev, D., et al, 2021., Geophys. Res. Let. [19] Olsen, K. et al., 2021. Nat. Geo. [20] Knutsen, E., et al., 2021, Icarus.

While space weather has been a growing field of research and applications over the last 15-20 years, “planetary space weather” is an emerging discipline. In fact, as long as we expand our robotic exploration within the solar system, monitoring planetary space weather is becoming more necessary than ever. Despite this, not every spacecraft is designed for plasma science and only a few of them have the necessary plasma instrumentation for space weather purposes. However, all of them have thousands of housekeeping detectors distributed along the spacecraft. In particular, energetic particles impact detectors and subsystems on a spacecraft and their effects can be identified in selected housekeeping data sets, such as the Error detection and correction (EDAC) counters. In this study, we investigate these engineering datasets for scientific purposes by performing the first feasibility study of solar energetic particle detection using EDAC counters from several available ESA Solar System missions, such as Mars Express, Rosetta, BepiColombo and Solar Orbiter. In order to validate the results, these detections are compared to other observations from scientific instruments on board these missions. Moreover, the potential implications of space weather event detections based on EDAC sensors at Mars and Comet 67P/Churyumov-Gerasimenko is analysed. This study has the potential to provide a good network of solar particle observations at locations where no scientific observations of this kind are available.

Compilation of processed data files used for the creation of the figures presented in the manuscript "Constraining near-surface water vapor on Mars: a spectral synergy climatological survey applied to PFS and SPICAM nadir observations".

The SuperCam instrument [1,2] onboard Mars2020 disposes of a variety of active and passive techniques, including passive spectroscopy in the 0.40-0.85 (VIS) and 1.3 to 2.6 microns (IR, [3,4]) wavelength ranges. Since the landing on Mars of Perseverance in February 2021, Supercam has acquired numerous observations of its near and distant environment, exploring the geological and mineralogical context of Jezero crater. In addition, several measurements were devoted to probing the atmosphere surrounding the Perseverance rover. The technique of using sky spectra in passive mode, known as “passive sky”, has already been demonstrated with ChemCam on the Mars Science Laboratory (MSL) rover [4]. SuperCam provides a superset of the ChemCam capabilities used in [4], and in particular adds a near-infrared component that includes absorption and scattering characteristics of key gases and aerosols/clouds. “Passive sky” measurements have typically been performed every other week to allow a consistent monitoring of the seasonal evolution of the main quantities (CO2, O2, H2O, CO, aerosols/clouds). Particular attention was given to joint measurements of O2 and CO, as they appear as key components of the Martian chemical cycle and have never been measured together at the same time on the surface of Mars. As the 2 μm wavelength region is used for the first time at the surface of Mars, it enables the detection of CO (around 2.35 μm). CO possesses a small absorption that has made it difficult to identify in SuperCam spectra so far. An overview of SuperCam’s progress to date in its attempt to characterize the Martian atmosphere at Jezero will be presented. References : [1] Wiens, R.C., et al. , 2021. Space Sci Rev 217, 4, [2] Maurice, S., et al., 2021. Space Sci Rev 217, 47, [3] Royer, C., et al.., 2020. Review of Scientific Instruments 91, 063105, [4] Fouchet, T., et al., 2021, Icarus, submitted. [5] McConnochie T. H et al., 2018. Icarus 307, 294

Telescope and detector developments continuously enable deeper and more detailed studies of astronomical objects. Larger collecting areas, improvement in dispersion and detector techniques, and higher sensitivities allow detection of more molecules in a single observation, at lower abundances, resulting in better constraints of the targets physical and chemical conditions. Improvements on current telescopes, and not to mention future observatories, both in space and on the ground, will continue this trend, ever improving our understanding of the Universe. Planetary exploration missions carry instrumentation to unexplored areas, and reveal details impossible to observe from the Earth by performing in-situ measurements. Space based observatories allow observations of object at wavelength ranges absorbed by the Earths atmosphere. The depth of understanding from all of these studies can be greatly enhanced by combining observations: ground-based and space-based, low-resolution and high-resolution, local and global-scale, similar observations over a broader or different spectra range, or by providing temporal information through follow-ups. Combined observations provide context and a broader scope of the studied object, and in this white paper, we outline a number of studies where observations are synergistically applied to increase the scientific value of both datasets. Examples include atmospheric studies of Venus, Mars, Titan, comets, Jupiter, as well as more specific cases describing synergistic studies in the Juno mission, and ground-based radar studies for near Earth objects. The examples aim to serve as inspiration for future synergistic observations, and recommendations are made based on the lessons learned from these examples.

Following the recent detection of HCl in the atmosphere of Mars by ExoMars/Trace Gas Orbiter, we present here the first measurement of the 37Cl/35Cl isotopic ratio in the Martian atmosphere using a set of Nadir Occultation for MArs Discovery (NOMAD) observations. We determine an isotopic anomaly of −6 ± 78‰ compared to Earth standard, consistent with the −51‰–−1‰ measured on Mars’ surface by Curiosity. The measured isotopic ratio is also consistent with surface measurements, and suggests that Cl reservoirs may have undergone limited processing since formation in the Solar Nebula. The examination of possible sources and sinks of HCl shows only limited pathways to short‐term efficient Cl fractionation and many plausible reservoirs of “light” Cl.

Isotopic ratios and, in particular, the water D/H ratio are powerful tracers of the evolution and transport of water on Mars. From measurements performed with ExoMars/NOMAD, we observe marked and rapid variability of the D/H along altitude on Mars and across the whole planet. The observations (from April 2018 to April 2019) sample a broad range of events on Mars, including a global dust storm, the evolution of water released from the southern polar cap during southern summer, the equinox phases, and a short but intense regional dust storm. In three instances, we observe water at very high altitudes (>80 km), the prime region where water is photodissociated and starts its escape to space. Rayleigh distillation appears the be the driving force affecting the D/H in many cases, yet in some instances, the exchange of water reservoirs with distinctive D/H could be responsible.

Galactic Cosmic Rays (GCRs) are an intrinsic part of the heliospheric radiation environment, and an inevitable challenge to long-term space exploration. Here we show solar cycle induced GCR modulation at Mars in the period 2005-2020, along with GCR radial gradients, by utilising Mars Express and Rosetta engineering parameters compared to sunspot number time series. The engineering parameter used is called EDAC (Error Detection And Correction), a cumulative counter which is triggered by charged energetic particle causing memory errors in on-board computers. EDAC data provides a new way of gaining insight into the field of particle transport in the heliosphere, allowing us to circumvent the need for dedicated instrumentation as EDAC software is present on all spacecraft. This data set can be used to capture variations of GCRs in both space and time, yielding the same qualitative information as ground-based neutron monitors. Our analysis of the Mars Express EDAC parameter reveals a strong solar cycle GCR modulation, yielding an anticorrelation coefficient of -0.5 at a time lag of ~5.5 months. By combining Mars Express with Rosetta data, we calculate a 5.3% increase in EDAC count rates per astronomical unit, attributed to a radial gradient in GCR fluxes in accordance with established literature. The potential of engineering data for scientific purposes remains mostly unexplored. The results obtained from this work demonstrates, for the first time for heliophysics purposes, the usefulness of the EDAC engineering parameter, data mining and the utility of keeping missions operational for many years, providing complimentary data to nominal science instruments.

Slightly less than a Martian Year of nominal science (March 2018–January 2020) with the ExoMars Trace Gas Orbiter has furthered the ongoing investigation of dayside water vapor column abundance. These dayside observations span latitudes between 75°S and 75°N, and all longitudes, which can provide global snapshots of the total water column abundances. In addition to tracking the seasonal transport of water vapor between poles, geographic enhancements are noted, particularly in the southern hemisphere, both in Hellas Basin, and in other regions not obviously correlated to topography. We report consistent water vapor climatology with previous spacecraft observations, however, note a difference in total water vapor content is noted. Finally, we are unable to find evidence for substantial diurnal variation in the total dayside water vapor column.

Methane (CH4) on Mars has attracted a great deal of attention since it was first detected in January 2003. As methane is considered a potential marker for past/present biological or geological activity, any possible detection would require evidence with strong statistical significance. Ethane (C2H6) and ethylene (C2H4) are also relevant chemical species as their shorter lifetimes in the Martian atmosphere make them excellent tracers for recent and ongoing releases. If detected, a CH4/C2H6 ratio could aid in constraining the potential source of organic production. Here we present the results of an extensive search for hydrocarbons in the Martian atmosphere in 240,000 solar occultation measurements performed by the ExoMars Trace Gas Orbiter/NOMAD instrument from April 2018 to April 2019. The observations are global, covering all longitudes and latitudes from 85 degrees N to 85 degrees S, and sampled from 6 to 100 km altitude with a typical vertical resolution of 2 km. There were no statistically significant detections of organics and new stringent upper limits for global ethane and ethylene were set at 0.1 ppbv and 0.7 ppbv, respectively. No global background level of methane was observed, obtaining an upper limit of 0.06 ppbv, in agreement with early results from ExoMars (Korablev et al., 2019). Dedicated searches for localized plumes at more than 2000 locations provided no positive detections, implying that if methane were released in strong and rapid events, the process would have to be sporadic.