Search

Formaldehyde (H2CO) is a critical precursor for the abiotic formation of biomolecules, including amino acids and sugars, which are the building blocks of proteins and RNA. Geomorphological and geochemical evidence on Mars indicates a temperate environment compatible with the existence of surface liquid water during its early history at 3.8–3.6 billion years ago (Ga), which was maintained by the warming effect of reducing gases, such as H2. However, it remains uncertain whether such a temperate and weakly reducing surface environment on early Mars was suitable for producing H2CO. In this study, we investigated the atmospheric production of H2CO on early Mars using a 1-D photochemical model assuming a thick CO2-dominated atmosphere with H2 and CO. Our results show that a continuous supply of atmospheric H2CO can be used to form various organic compounds, including amino acids and sugars. This could be a possible origin for the organic matter observed on the Martian surface. Given the previously reported conversion rate from H2CO into ribose, the calculated H2CO deposition flux suggests a continuous supply of bio-important sugars on early Mars, particularly during the Noachian and early Hesperian periods. [ABSTRACT FROM AUTHOR]

NOMAD is a suite of spectrometers on the board of the ESA-Roscosmos Trace Gas Orbiter (TGO) spacecraft and is capable of investigating the Martian environment at very high spectral resolution in the ultraviolet–visible and infrared spectral ranges by means of three separate channels: UVIS (0.2–0.65 μm), LNO (2.2–3.8 μm), and SO (2.3–4.3 μm). Among all channels, LNO is the only one operating at infrared wavelengths in nadir-viewing geometry, providing information on the whole atmospheric column and on the surface. Unfortunately, the LNO data are characterized by an overall low level of signal-to-noise ratio (SNR), limiting their contribution to the scientific objectives of the TGO mission. In this study, we assess the possibility of enhancing LNO nadir data SNR by applying the Minimum Noise Fraction (MNF), a well-known algorithm based on the Principal Components technique that has the advantage of providing transform eigenvalues ordered with increasing noise. We set up a benchmark process on an ensemble of synthetic spectra in order to optimize the algorithm specifically for LNO datasets. We verify that this optimization is limited by the presence of spectral artifacts introduced by the MNF itself, and the maximum achievable SNR is dependent on the scientific purpose of the analysis. MNF application study cases are provided to LNO data subsets in the ranges 2.627–2.648 μm and 2.335–2.353 μm (spectral orders 168 and 189, respectively) covering absorption features of gaseous H2O and CO and CO2 ice, achieving a substantial enhancement in the quality of the observations, whose SNR increases up to a factor of 10. While such an enhancement is still not enough to enable the investigation of spectral features of faint trace gases (in any case featured in orders whose spectral calibration is not fully reliable, hence preventing the application of the MNF), interesting perspectives for improving retrieval of both atmospheric and surface features from LNO nadir data are implied. [ABSTRACT FROM AUTHOR]

Precipitation of solar energetic particles (SEPs) into planetary atmospheres causes changes in atmospheric chemical composition through ionization, dissociation, and excitation of atmospheric molecules. In contrast to the terrestrial atmosphere, where depletion of ozone in the polar mesosphere has been studied by observations and models for decades, there have been no studies on the effects of SEPs on the neutral chemical composition of Mars' present‐day atmosphere. This study provided the first estimate of the impacts of SEPs on neutral chemical composition in the present‐day Martian atmosphere coupling a Monte Carlo model and a one‐dimensional photochemical model. Our results showed that ozone density in the Martian atmosphere might decrease in the altitude range of 20–60 km with a factor 10 maximum enhancement occurring at 40 km during a Halloween‐class SEP event due to an enhanced concentration of HOx. The depletion of ozone occurred in the altitude range of 20–60 km, corresponding to the penetration of protons with an energy range of 4.6–46 MeV. Such ozone depletion should be detected by Trace Gas Orbiter/Nadir and Occultation for MArs Discovery during intense SEP event. A 75% depletion of the ozone density at 40 km can be expected during SEP events occurring once in every 1 year. Therefore, ozone concentration in the Martian atmosphere might sufficiently decrease during a SEP event as on Earth, but through different chemical pathways driven by CO2 ionization and CO recombination catalytic cycle. Key Points: The solar energetic particle (SEP) effects on the neutral chemical composition in the Martian atmosphere are investigated by numerical simulationsOzone depletion due to enhanced HOx during a large SEP event could be detected by Trace Gas Orbiter/Nadir and Occultation for MArs DiscoveryChemical pathways leading to ozone depletion on Mars differ from those on Earth [ABSTRACT FROM AUTHOR]

Since the beginning of the Trace Gas Orbiter (TGO) science operations in April 2018, its instrument "Nadir and Occultation for MArs Discovery" (NOMAD) supplies detailed observations of the IR spectrums of the Martian atmosphere. We developed a procedure that allows us to evaluate the composition and distribution's parameters of the atmospheric Martian aerosols. We use a retrieval program (RCP) in conjunction with a radiative forward model (KOPRA) to evaluate the vertical profile of aerosol extinction from NOMAD measurements. We then apply a model/data fitting strategy of the aerosol extinction. In this first article, we describe the method used to evaluate the parameters representing the Martian aerosol composition and size distribution. MY 34 GDS showed a peak intensity from LS 190° to 210°. During this period, the aerosol content rises multiple scale height, reaching altitudes up to 100 km. The lowermost altitude of aerosol's detection during NOMAD observation rises up to 30 km. Dust aerosols reff were observed to be close to 1 μm and its νeff lower than 0.2. Water ice aerosols reff were observed to be submicron with a νeff lower than 0.2. The vertical aerosol structure can be divided in two parts. The lower layers are represented by higher reff than the upper layers. The change between the lower and upper layers is very steep, taking only few kilometers. The decaying phase of the GDS, LS 210°–260°, shows a decrease in altitude of the aerosol content but no meaningful difference in the observed aerosol's size distribution parameters. Plain Language Summary: Mars' atmosphere is filled with dust and water ice particles carried by the winds. These aerosols affect the way sunlight is distributed in the atmosphere and on the surface, and this directly affects temperature. In addition, approximately every three Martian years, Mars experiences what is known as a "global dust storm." This type of dust storm covers the entire red planet in dust. It affects the temperature and water vapor content of the Martian atmosphere. Determining and assessing aerosol properties, number, size and mass during and after a global dust storm is of crucial importance to understanding its underlying mechanisms. Here, we develop an analysis scheme to study the size, nature, number and distribution of Martian aerosols. Our study confirms that, overall, dust and water ice particles are quite small, close to 1 μm or even smaller, and that a global dust storm affects the intensity of other storms that follow. Key Points: Retrieval of Martian aerosols key properties from NOMAD‐SO data during the MY 34 GDSMesospheric dust and water ice reff are mainly ∼1 μm and ≤0.5 μm respectively during the MY 34 GDS and its decay phaseDuring the MY 34 GDS, the effective variance shows a slight N/S asymmetry and values mainly ≤0.2 [ABSTRACT FROM AUTHOR]

Observations of water ice clouds and aerosols on Mars can provide important insights into the complexity of the water cycle. Recent observations have indicated an important link between dust activity and the water cycle, as intense dust activity can significantly raise the hygropause, and subsequently increase the escape of water after dissociation in the upper atmosphere. Here present observations from Nadir and Occultation for MArs Discovery/Trace Gas Orbiter that investigate the variation of water ice clouds in the perihelion season of Mars year 34 (April 2018–2019), their diurnal and seasonal behavior, and the vertical structure and microphysical properties of water ice and dust. These observations reveal the recurrent presence of a layer of mesospheric water ice clouds subsequent to the 2018 global dust storm. We show that this layer rose from 45 to 80 km in altitude on a time scale of days from heating in the lower atmosphere due to the storm. In addition, we demonstrate that there is a strong dawn‐dusk asymmetry in water ice abundance, related to nighttime nucleation and subsequent daytime sublimation. Water ice particle sizes are retrieved consistently and exhibit sharp vertical gradients (from 0.1 to 4.0 μm), as well as mesospheric differences between the global dust storm (<0.5 μm) and the 2019 regional dust storm (1.0 μm), which suggests differing water ice nucleation efficiencies. These results form the basis to advance our understanding of mesospheric water ice clouds on Mars, and further constrain the interactions between water ice and dust in the middle atmosphere. Key Points: Water vapor condensation rapidly responds to dust storms, increasing the altitude of mesospheric cloud formationClouds structure is observed to change between dawn and dusk, indicating nighttime nucleation of water ice on dust particlesVertical gradients in water ice particle size relate to water vapor and nuclei availability, which vary between the two dust storms of MY34 [ABSTRACT FROM AUTHOR]

The NOMAD ("Nadir and Occultation for MArs Discovery") spectrometer suite on board the ExoMars Trace Gas Orbiter has been designed to investigate the composition of Mars' atmosphere, with a particular focus on trace gases, clouds and dust. This will allow for a major leap in our knowledge and understanding of the Martian atmospheric composition and the related physical and chemical processes. NOMAD will conduct a spectroscopic survey of Mars' atmosphere in ultraviolet (UV), visible and infrared (IR) wavelengths covering large parts of the 0.2-4.3 µm spectral range [1,2]. NOMAD is composed of 3 spectrometers: a solar occultation dedicated spectrometer (SO – Solar Occultation) operating in the infrared (2.3-4.3 µm), a second infrared spectrometer (2.3-3.8 µm) capable of doing nadir, but also solar occultation and limb observations (LNO – Limb Nadir and solar Occultation) [3], and an ultraviolet/visible spectrometer (UVIS – UV visible, 200-650 nm) that can work in all three observation modes [4].Science phase started in April 2018. Since then NOMAD performed solar occultation and nadir observations using different options to test the instrument under various conditions. Several atmospheric species have been targeted, delivering profiles from solar occultation from 200 km down to the surface and integrated abundances from nadir measurements. Observations optimized for the detection of dust and clouds have also been performed. We will present first results from nadir and solar occultation observations, with an emphasis on the detection of the dust storm observed in June 2018 and afterwards, and its impact on the composition of the atmosphere in particular on water and D/H ratio. References[1] Vandaele, A.C., et al., 2015. Planet. Space Sci. 119, 233-249.[2] Vandaele et al., 2018. Space Sci. Rev., 214:80, doi.org/10.1007/s11214-11018-10517-11212.[3] Neefs et al., 2015. Applied Optics 54, 8494-8520.[4] Patel et al., 2017. Applied Optics 56, 2771-2782. [ABSTRACT FROM AUTHOR]

Nadir and Occultation for MArs Discovery (NOMAD) is a 3-channel spectrometer suite that is currently orbiting Mars onboard ESA's ExoMars Trace Gas Orbiter, measuring the composition of the Martian atmosphere in unprecedented detail. Of the three channels, two operate in the infrared: the Solar Occultation (SO) channel observes gas species in the 2.2–4.3 ​μm spectral region in solar occultation mode, while the Limb, Nadir and Occultation (LNO) channel observes in the 2.2–3.8 ​μm spectral region and can operate in limb-, nadir- and solar occultation-pointing modes. The Ultraviolet–VISible (UVIS) channel operates in the UV–visible region, from 200 to 650 ​nm. Both infrared channels have a spectral resolution typically an order of magnitude better than previous instruments orbiting Mars, to measure molecular absorption lines and therefore determine the abundances of constituents of the Martian atmosphere and the processes that govern their distribution and transport. To maximise the full potential of the instrument, a wide range of calibration measurements were made prior to launch and continue to be made in-flight. This work, part 1, addresses the aspects of the SO channel calibration that are not covered elsewhere, namely: the SO channel ground calibration setup, boresight pointing vector determination, detector characterisation, detector illumination pattern and saturation levels, and an investigation of the instrument line shape. An accompanying paper, part 2, addresses similar aspects for LNO, the other infrared channel in NOMAD (Thomas et al., 2021, this issue). [ABSTRACT FROM AUTHOR]

We investigate water vapor saturation in the martian atmosphere in the presence or proximity of water ice clouds. We evaluate mixing ratio profiles of ambient water vapor derived from measurements by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and the Nadir and Occultation for MArs Discovery (NOMAD) instrument in comparison with saturated vapor mixing ratio profiles derived from co-located temperature measurements by the Mars Climate Sounder (MCS). We find that during the aphelion season the average saturation state of the atmosphere is close to saturation in the presence of clouds, with supersaturation ratios reaching values of no more than two to three towards the top of the cloud layer. During the perihelion season, subseasonally averaged water vapor is close to saturation or somewhat subsaturated in the presence of clouds, with some supersaturation at southern high latitudes towards the top of the clouds. Measurements at northern mid- to high latitudes during a Global Dust Storm suggest a shift of the cloud occurrence to higher altitudes but exhibit a similar saturation structure, with supersaturations not exceeding a ratio of five. The atmosphere above cloud layers is largely subsaturated, suggesting that cloud formation is fairly instantaneous upon the temperature dropping below the frost point and high levels of supersaturation are not required to form water ice clouds. We propose a schematic model of cloud evolution in which small cloud particles are formed rapidly in slightly supersaturated regions, and then fall and grow such that ice opacity is still observed even in the subsaturated regions below. [Display omitted] • Water vapor saturation close to clouds in the martian atmosphere is investigated. • The average state of the atmosphere is close to saturation. • The atmosphere above and below cloud layers appears largely subsaturated. • High levels of supersaturation are not required to form water ice clouds. [ABSTRACT FROM AUTHOR]

More than a full Martian year of observations have now been made by the Nadir Occultation for MArs Discovery (NOMAD) instrument suite on-board the ExoMars Trace Gas Orbiter. Radiative transfer modeling of NOMAD observations taken in the nadir geometry enable the seasonal and global-scale variations of carbon monoxide gas in the Martian atmosphere to be characterized. These retrievals show the column-averaged volume mixing ratio of carbon monoxide to be about 800 ppmv, with significant variations at high latitudes caused by the condensation and sublimation of the background CO 2 gas. Near summer solstice in each hemisphere, the CO volume mixing ratio falls to 400 ppmv in the south and 600 ppmv in the north. At low latitudes, carbon monoxide volume mixing ratio inversely follows the annual cycle of surface pressure. Comparison of our retrieved CO volume mixing ratio against that computed by the GEM-Mars general circulation model reveals a good match in their respective seasonal and spatial trends, and can provide insight into the physical processes that control the distribution of CO gas in the current Martian atmosphere. • The global, seasonal distribution of CO gas is retrieved from NOMAD nadir observations. • Globally averaged CO abundance is ~800 ppm, but with strong seasonal variations. • GCM modeling can provide insight into physical processes behind retrieved abundances. [ABSTRACT FROM AUTHOR]

Methane (CH 4) 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 (C 2 H 6) and ethylene (C 2 H 4) 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 CH 4 /C 2 H n 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°N to 85°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. • A full year of Mars observation with global coverage yield no methane detections. • Search for global background level as well as localized plumes were conducted. • Methane upper limits down to 0.06 ppbv, lower than previous detections, were obtained above an altitude of 6 km. • Search for ethane and ethylene gave upper limits of 0.1 and 0.7 ppbv respectively. [ABSTRACT FROM AUTHOR]

Eventual past forms of life on Mars and future human missions have been and will be strongly affected by radiation. Here we present the estimation of the radiation environment (Galactic Cosmic Rays, GCRs, and Solar Energetic Particles, SEPS) and corresponding doses in proxies for biological targets at Oxia Planum, chosen as the landing site for the next ExoMars 2020 mission [1], and Mawrth Vallis, previously a candidate landing site. The study is performed through detailed Monte Carlo particle transport calculations using the dMEREM code [2] based on the Geant4 toolkit [3], for the period of the Halloween storm (October 2003).The results [4] show that both elevation (and thus atmospheric depth) and mineralogical content influence the doses received at the surface of the two sites. In particular, we find that the spectra of downward GCRs are slightly influenced by differences in the atmospheric depth, while SEPs, being more stopped in the upper part of the atmosphere, have a downward spectrum relatively similar for the two locations. The different behavior of the two types of radiation is also analyzed in their interaction with the regolith. The influence of diurnal variations of the atmosphere on the radiation environment are also studied, and compared with the observations from Curiosity [5]. For the two sites mentioned above and also for Gale Crater, an underestimation of the radiobiological doses can be noted. We speculate that the Monte Carlo particle transport approach partially understimate the radiation damage at lower energies, as also demonstrated by some few previous works, and we present our current efforts in better understanding how to model the effects of radiation across different energy/lengths scales [6].This work is initiated in the context of the EU H2020 project ESC2RAD "Enabling Smart Computations to study space RADiation Effects", Grant 776410 [6].[1] Jorge L. Vago, Frances Westall, Pasteur Instrument Team, Landing Site Selection Working Group, and Other Contributors: Habitability on Early Mars and the Search for Biosignatures with the ExoMars Rover, Astrobiology Vol. 17, pp. 471-501, 2017[2] McKenna-Lawlor S., Gonçalves P., A. Keating A., Morgado B., Heynderickx D., P. Nieminen P., Santin G., Truscott P., Lei F., Foing B., Balaz J.: Characterization of the particle radiation environment at three potential landing sites on Mars using ESA's MEREM models, Icarus Vol. 218, pp. 723–734, 2012[3] https://geant4.web.cern.ch/[4] F. Da Pieve et al, in preparation[5] Hassler, D., Cary Zeitlin M., F. Wimmer-Schweingruber R., Ehresmann B., Rafkin S., L. Eigenbrode J., E. Brinza D., Weigle G., Böttcher S., Böhm E., Burmeister S., Guo J., Köhler J., Martin S, Reitz G., A. Cucinotta F., Kim M.-H., Grinspoon D., A. Bullock M., Posner A., Gómez-Elvira J., Vasavada A., Grotzinger J.P., MSL Science Team (2014). Mars' surface radiation environment measured with the Mars Science laboratory's curiosity rover. Science 343, 1244797[6] www.esc2rad.eu [ABSTRACT FROM AUTHOR]