Planet. Sci. J. 2 238     DOI 10.3847/PSJ/ac38a4 10.3847/PSJ/ac38a4

Kruss M., Salzmann T., Parteli E., Jungmann F., Teiser J., Schönau L., Wurm G.

It is a long-standing open question whether electrification of wind-blown sand due to tribocharging—the generation of electric charges on the surface of sand grains by particle–particle collisions—could affect rates of sand transport occurrence on Mars substantially. While previous wind tunnel experiments and numerical simulations addressed how particle trajectories may be affected by external electric fields, the effect of sand electrification remains uncertain. Here we show, by means of wind tunnel simulations under air pressure of 20 mbar, that the presence of electric charges on the particle surface can reduce the minimal threshold wind shear velocity for the initiation of sand transport, u_*ft, significantly. In our experiments, we considered different samples, a model system of glass beads as well as a Martian soil analog, and different scenarios of triboelectrification. Furthermore, we present a model to explain the values of u_*ft obtained in the wind tunnel that is based on inhomogeneously distributed surface charges. Our results imply that particle transport that subsides, once the wind shear velocity has fallen below the threshold for sustained transport, can more easily be restarted on Mars than previously thought.

Schematical diagram of the main relevant forces acting on a particle that is protruding from the granular bed considered in our experiments.

2023 (JGR) https://doi.org/10.1029/2022EA002429

A. Piccialli, A. C. Vandaele, Y. Willame, A. Määttänen, L. Trompet, J. T. Erwin, F. Daerden, L. Neary, S. Aoki, S. Viscardy, I. R. Thomas, C. Depiesse, B. Ristic, J. P. Mason, M. R. Patel, M. J. Wolff, A. S. J. Khayat, G. Bellucci, J.-J. Lopez-Moreno

The NOMAD-UVIS instrument on board the ExoMars Trace Gas Orbiter has been investigating the Martian atmosphere with the occultation technique since April 2018. Here, we analyze almost two Mars Years of ozone vertical distributions acquired at the day-night terminator. The ozone retrievals proved more difficult than expected due to spurious detections of ozone caused by instrumental effects, high dust content, and very low values of ozone. This led us to compare the results from three different retrieval approaches: (a) an onion peeling method, (b) a full occultation Optimal Estimation Method, and (c) a direct onion peeling method. The three methods produce consistently similar results, especially where ozone densities are higher. The main challenge was to find reliable criteria to exclude spurious detections of O3, and we finally adopted two criteria for filtering: (a) a detection limit, and (b) the Δχ2 criterion. Both criteria exclude spurious O3 values especially near the perihelion (180° < Ls < 340°), where up to 98% of ozone detections are filtered out, in agreement with general circulation models, that expect very low values of ozone in this season. Our agrees well with published analysis of the NOMAD-UVIS data set, as we confirm the main features observed previously, that is, the high-altitude ozone peak around 40 km at high latitudes. The filtering approaches are in good agreement with those implemented for the SPICAM/MEx observations and underline the need to evaluate carefully the quality of ozone retrievals in occultations.

Seasonal evolution of FOEM ozone abundance observed by NOMAD-UVIS for different latitude ranges. Left panels show the ozone retrievals without any filtering; in the middle panels we applied the DL filter; and in the right panels we applied both the DL and Δχ2 filters.

2023 (PSJ) https://doi.org/10.3847/PSJ/acd32f 

S. Aoki, K. Shiobara, N. Yoshida, L. Trompet, T. Yoshida, N. Terada, H. Nakagawa, G. Liuzzi, A. C. Vandaele, I. R. Thomas, G. L. Villanueva, M. A. Lopez-Valverde, A. Brines, M. R. Patel, S. Faggi, F. Daerden, J. T. Erwin, B. Ristic, G. Bellucci, J. J. Lopez-Moreno, H. Kurokawa and Y. Ueno

The atmosphere of Mars is mainly composed by carbon dioxide (CO₂). It has been predicted that photodissociation of CO₂ depletes ¹³C in carbon monoxide (CO). We present the carbon ¹³C/¹²C isotopic ratio in CO at 30–50 km altitude from the analysis of the solar occultation measurements taken by the instrument Nadir and Occultation for Mars Discovery on board the ExoMars Trace Gas Orbiter (ExoMars-TGO). We retrieve ¹²C¹⁶O, ¹³C¹⁶O, and ¹²C¹⁸O volume mixing ratios from the spectra taken at 4112–4213 cm⁻¹, where multiple CO isotope lines with similar intensities are available. The intensities of the ¹²C¹⁶O lines in this spectral range are particularly sensitive to temperature, thus we derive the atmospheric temperature by retrieving CO₂ density with simultaneously measured spectra at 2966–2990 cm⁻¹. The mean δ¹³C value obtained from the ¹³C¹⁶O/¹²C¹⁶O ratios is −263‰, and the standard deviation and standard error of the mean are 132‰ and 4‰, respectively. The relatively large standard deviation is due to the strong temperature dependences in the ¹²C¹⁶O lines. We also examine the ¹³C¹⁶O/¹²C¹⁸O ratio, whose lines are less sensitive to temperature. The mean δ value obtained with ¹²C¹⁸O instead of ¹²C¹⁶O is −82‰ with smaller standard deviation, 60‰. These results suggest that CO is depleted in ¹³C when compared to CO₂ in the Martian atmosphere as measured by the Curiosity rover. This depletion of ¹³C in CO is consistent with the CO₂ photolysis-induced fractionation, which might support a CO-based photochemical origin of organics in Martian sediments.

Synthetic spectra of the NOMAD measurements taken with diffraction order 183 (a), order 184 (b), order 185 (c), and order 186 (b) around 30 km tangent height. The assumed vertical profile of total CO volume mixing ratio is 1000 ppm (uniform) and along the line of sight. The isotopic ratios defined in the HITRAN2020 databases are assumed. The red, blue, and green curves illustrate contributions due to ¹²C¹⁶O, ¹³C¹⁶O, and ¹²C¹⁸O absorption lines. The origin of the Y-axis for the red, blue, and green curves have been offset to improve visibility.

2023 (JGR) https://doi.org/10.1029/2022JE007279

L. Trompet, A.C. Vandaele, I. Thomas, S. Aoki, F. Daerden, J. Erwin, Z. Flimon, A. Mahieux, L. Neary, S. Robert, G. Villanueva, G. Liuzzi, Lopez Valverde, A. Brines, G. Bellucci, J. J. Lopez-Moreno, M. R. Patel

The Solar Occultation (SO) channel of the Nadir and Occultation for Mars Discovery (NOMAD) instrument scans the Martian atmosphere since 21 April 2018. In this work, we present a subset of the NOMAD SO data measured at the mesosphere. We focused on a spectral range that started to be recorded in Martian Year (MY) 35. A total of 968 vertical profiles of carbon dioxide density and temperature covering MY 35 and the beginning of MY 36 are investigated until 135° of solar longitude. We compared 47 profiles with co-located profiles of Mars Climate Sounder onboard Mars Reconnaissance Orbiter. Most profiles show a good agreement as SO temperatures are only 1.8 K higher but some biases lead to an average absolute difference of 7.4°K. The SO dataset is also compared with simulations from GEM-Mars general circulation model. Both datasets are in good agreement except for the presence of a cold layer in the winter hemisphere and a warm layer at dawn in the Northern hemisphere for solar longitudes between 240° to 360°. Five profiles contain temperatures lower than the limit for CO2 condensation. Strong warm layers are found in 13.5% of the profiles. They are present mainly at dawn and in the winter hemisphere while the Northern dusks appear featureless. The dataset mainly covers high latitudes around 60° and we derived some non-migrating tides. In the Southern winter hemisphere, we derived apparent zonal wavenumber-1 and wavenumber-3 tidal components with a maximum amplitude of 10% and 5% at 63 km, respectively.

Panel a) six temperature profiles for diffraction order 148 with some values lower than the temperature limit for CO2
condensation. Panel b) transmittances at pixel 180 corresponding to the profiles in panel a. The second Y-axis provides rough
altitude values.