TP6

We applied advanced light-scattering models on laboratory measurements to retrieve the scattering properties of Martian dust analogues JSC Mars-1, MMS-2, and MGS-1. The retrieval was performed in two parts: first, we computed the optical constants of the three samples. Then, the obtained values were used together with two different scattering databases to model the measured scattering matrices of the samples.

Optical constants are needed from modelling single-scattering within the atmospheric dust to simulating the global Martian climate. Reliable complex refractive indices of Martian dust are difficult to find in the literature. Previous studies by Wolff et al. (2009) & (2010) have obtained optical constants from analysing the observed dust storm spectra at 258-2900 nm region by using cylindrical particle shapes. However, these values could not be supported with direct laboratory measurements. In this work, we retrieved the complex refractive indices of the three Martian dust analogues at UV-vis-NIR wavelengths by using the measured size distributions, diffuse reflectance spectra, and an advanced light-scattering model with realistic particle shapes. 

The scattering properties of the analogues were retrieved by utilizing the derived refractive indices, measured scattering matrices, and two databases of single scattering properties of triaxial ellipsoids (Meng et al. 2010) and hexahedral shapes (Saito et al. 2021) The databases have been developed by a combination of three computational methods: the T-matrix method, the discrete dipole approximation (DDA), and an improved geometric optics method. Each database consists of pre-calculated scattering properties over a broad range of complex refractive indices, particle sizes, particle shapes, and wavelengths. The modelled scattering matrices were then compared with those obtained using spherical shapes. Finally, the best-fit model gives us physical properties of the particles such as cross sections, single scattering albedos, extinction efficiencies, asymmetry factors, and Legendre polynomials used to mathematically calculate the phase functions.

References: Wolff et al. (2009), JGR Planets, 114, E00D04 ; Wolff et al. (2010), Icarus, 208, 143-155 ; Meng et al. (2010), J. Atmos. Sci., 41.5: 501-512 ; Saito et al. (2021), J. Atmos. Sci., 78, 2089-2111.

How to cite: Martikainen, J., Muñoz, O., Jardiel, T., Peiteado, M., Gómez Martín, J. C., and Team, T. R.: Retrieving scattering properties of Martian dust analogues by modelling light scattering, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-75, https://doi.org/10.5194/epsc2022-75, 2022.

Polarimetry of sunlight that is reflected by a planet or that is transmitted through its atmosphere is a powerful tool for the characterisation of the planetary atmosphere and, if present, the surface. The main reason for the power of polarimetry is that the angular distribution of the degree of linear polarisation of sunlight that has been singly scattered by particles in the atmosphere or on the surface is very sensitive to the microphysical properties of these particles (their size, shape, and composition), indeed much more sensitive than the total flux is [see 1, 2, 3]. And because multiple scattered light usually has a low degree of polarisation, it might decrease the overall degree of polarisation of the light that emerges from the planetary atmosphere, but the angular pattern, which holds the crucial information about the scatterers, will remain. A classic example of the power of polarimetry was the derivation of the size distribution, composition, and altitude of the particles constituting Venus’s main cloud deck from Earth-based, disk-integrated polarimetry across a wide phase angle range and at a few wavelengths [4]. Since then, spectrometers with some polarimetric capabilities have flown on, for example, the Pioneer Venus, Galileo, and Cassini missions. The POLDER polarimeter has flown on various Earth observing missions, and NASA’s Earth remote-sensing PACE mission with SPEXone [5] onboard is scheduled for launch in 2024.

Mars, with its dust storms, its water and carbon-dioxide ice clouds, and dusty surface, appears to be an ideal target for polarimetry. The polarimetric attention for this planet has, however, been surprisingly limited. Two linear polarimeters have flown onboard the Soviet spacecraft MARS-5 and provided some information about mostly ice cloud particle shapes, sizes, and composition, even though they encountered a very clear Martian atmosphere during their short active measurement period [6, 7]. And, indeed, HST observations show linear polarisation variations that correlate with the presence of clouds and dust [8]. However, with HST orbiting the Earth, these observations were necessarily done with Mars at a small phase angle; the measured degrees of polarization are therefore very small and the angular range extremely limited. To truly enjoy the advantages of polarimetry for Mars remote-sensing, a polarimeter should either orbit the planet or be landed on the surface, because only then a range of scattering angles holding most of the information would be within reach.

We will describe the case for martian spectropolarimetry from an orbiter or a lander/rover, highlighting the potential for characterisation of the atmospheric dust and clouds and of the surface, and also covering the use of circular polarimetry for identifying chiral signatures [9,10] that on Earth are typical for life.  Traditionally, polarimeters have been based on polarisers in rotating filter wheels. Such designs are neither robust nor do they achieve the accuracy that fully unlocks the power of polarimetry. We will present an innovative, compact, robust (no moving parts), and accurate type of spectropolarimeter [11] whose flexible design allows incorporation on various vehicles. Finally, the analysis and interpretation of martian spectropolarimetric measurements requires radiative transfer algorithms that fully include linear (and circular) polarimetry. We will describe a few available algorithms and discuss laboratory measurements of light scattering properties of various types of atmospheric particles and surfaces that would improve the radiative transfer computations and with that the interpretation of (future) spectropolarimetry of Mars.       

References

[1] J. E. Hansen and L. D. Travis. Light scattering in planetary atmospheres. Space Sci. Rev., 16:527–610, 1974. 

[2] M. I. Mishchenko and L. D. Travis. Satellite retrieval of aerosol properties over the ocean using polarization as well as intensity of reflected sunlight. J. Geophys. Res., 102:16989–17014. doi: 10.1029/96JD02425, 1997

[3] Y. Shkuratov, N. Opanasenko, E. Zubko, Y. Grynko, V. Korokhin, C. Pieters, G. Videen, U. Mall, and A. Opanasenko. Multispectral polarimetry as a tool to investigate texture and chemistry of lunar regolith particles. Icarus, 187:406–416. doi: 10.1016/j.icarus. 2006.10.012, 2007 

[4] J. E. Hansen and J. W. Hovenier. Interpretation of the Polarization of Venus. J. Atmos. Sci., 31:1137–1160, 1974. 

[5] F. Snik, J. H. Rietjes, G. Van Harten, D. M. Stam, C. U. Keller, J. M. Smit. SPEX: the spectropolarimeter for planetary exploration. Proc. SPIE 7731:77311B. doi: 10.1117/12.857941, 2010.

[6] R. Santer, M. Deschamps, L. V. Ksanfomaliti, and A. Dollfus. Photopolarimetric analysis of the Martian atmosphere by the Soviet MARS-5 orbiter. I - White clouds and dust veils. Astron. Astrophys., 150:217–228, 1985. 

[7] R. Santer, M. Deschamps, L. V. Ksanfomaliti, and A. Dollfus. Photopolarimetry of Martian aerosols. II - Limb and terminator measurements. Astron. Astrophys., 158:247–258, 1986.

[8] Y. Shkuratov, M. Kreslavsky, V. Kaydash, G. Videen, J. Bell, M. Wolff, M. Hubbard, K. Noll, and A. Lubenow. Hubble Space Telescope imaging polarimetry of Mars during the 2003 opposition. Icarus, 176:1–11. doi: 10.1016/j.icarus.2005.01.009, 2005

[9] W. Sparks, J. H. Hough, Th. A. Germer, F. Robb, and L. Kolokolova, Remote sensing of chiral signatures on Mars, Planet. Space Sci. 72, doi: 10.1016/j.pss.2012.08.010, 2012

[10] W. Sparks, J. H. Hough, and L. E. Bergeron, The search for chiral signatures on Mars, Astrobiology, 5, doi: 10.1089/ast.2005.5.737, 2005

[11] D. M. Stam, E. Laan, F. Snik, T. Karalidi, C. Keller, R. ter Horst, R. Navarro, C. Aas, J. De Vries, G. Oomen, R. Hoogeveen, Polarimetry of Mars with SPEX, an innovative spectropolarimeter, Third International Workshop on The Mars Atmosphere: Modeling and Observations, LPI Contributions, Vol. 1447, 2008. 

How to cite: Stam, D.: Spectropolarimetry of Mars: Why and how?, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-675, https://doi.org/10.5194/epsc2022-675, 2022.

Introduction

The nature, size and content of aerosols in the atmosphere affect the energy budget on all planets, hence the atmospheric dynamic of the planet. Mars exhibits three types of atmospheric aerosol. Mineral dust, water ice and carbon dioxide ice. Martian aerosols nature and size distribution were observed using many different methods and experiments, from rovers to satellites. Exhaustive review scan be found in [1] and in [2]. Usually, dust effective radius, r_eff, ranges from 1 to 2 μm and its effective variance, ν_eff, from 0.2 to 0.4. H₂O ice r_eff ranges from 1 to 5 μm and its ν_eff from 0.1 to 0.4. However, these two parameters and their variability are poorly constraint in the vertical to date. ExoMars TGO mission (ESA/Roscosmos) was primarily designed to study trace gases, thermal structure and aerosol content in Mars atmosphere with unprecedented vertical resolution [3].

NOMAD-SO Data processing

NOMAD (Nadir and Occultation for MArs Discovery) is suite of two infrared spectrometers onboard the ExoMars 2016 Trace Gas Orbiter (TGO) orbiter, covering the spectral range of 0.2 to 4.3 μm [4]. An Acousto-Optical Tunable Filter (AOTF) is used to select different spectral windows. The sampling of this channel is approximately of 1 second, allowing a vertical sampling about 1km. the SO channel is able to observe the atmosphere at a given altitude with 6 different diffraction orders. For this study, we selected a configuration of 5 diffraction orders (121,134,149,168,190) effectively spanning the overall spectral range of NOMAD.

In order to evaluate the local extinction due to aerosols, we use an inversion program called Retrieval Control Program (RCP). It is a multi-parameter non-linear least squares fitting of measured and modelled spectra [5]. Its forward model, KOPRA, was recently adapted to limb emissions on Mars [6] and for solar occultation data on Mars for the first time. RCP solves iteratively the inverse problem [7] and is described in details in [8]. The regularization matrix is build from Tikhonov-type terms of different orders which can be combined to obtain a custom-tailored regularization for any particular retrieval problem.

An example of the retrieved extinction profile is shown in Fig 1. The retrieved extinctions differs from previous work on aerosols using ACS data [9,10]  using the Onion-peeling or Abel's transform method since this global fit is less affected by the large error propagation to low altitudes typical of those methods, and the lower Martian atmosphere is precisely where aerosols are particular relevant.

Fig 1.

Mean extinction cross-section ratio modelling

In order to model the optical behavior of the Martian aerosol we chose the log-normal distribution which is widely used in atmospheric sciences. It is a function of two parameters (r_g, σ_g). In optics, we change those parameters to more suitable ones, the effective radius, r_eff and its corresponding effective variance ν_eff. For any aerosol size distribution, the extinction k is km^-1 is k(λ) = N . σ_ext (λr_eff,ν_eff). N is the aerosol number density and σ_ext (λ,r_eff,ν_eff) is the mean average extinction cross-section at a wavelength λ, a specific aerosol distribution defined by (r_eff,ν_eff). We build a look-up table of dust and water ice σ_ext at the selected NOMAD order's wavelengths for different sets of (r_eff,ν_eff). The extinction are evaluated with a Lorenz-Mie code for polydisperse spherical particle from [11].

Aerosol composition and size distribution evaluation

We will detail the process of evaluating the aerosol composition and size distribution that consists of a mix of non-linear least square and brute force in order to evaluate the best set of parameters (r_eff,ν_eff ,γ) where γ represent a mixture of dust and H₂O ice_. The NLSQ algorithm is provided by the SciPy Python package [12]. To assess the robustness and limitations of our evaluation procedure, we will present results against synthetic extinction signal. We will discuss our main results, especially for the period covering the Global Dust Storm of MY34 (Fig 2.).

Fig 2.

Acknowledgments

The IAA/CSIC team acknowledges financial support from the State Agency for Research of the Spanish MCIU through the \emph{"Center of Excellence Severo Ochoa"} award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709) and funding by grant PGC2018-101836-B-100 (MCIU/AEI/FEDER, EU). ExoMars is a space mission of the European Space Agency (ESA) and Roscosmos. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB-BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University).

References

[1] Robert M. Haberle et al., eds. The Atmosphere and Climate of Mars. Cambridge University Press, 2017.

[2] R. Todd Clancy et al. “The distribution, composition, and particle properties of Mars meso-spheric aerosols: An analysis of CRISM visible/near-IR limb spectra with context from near-coincident MCS and MARCI observations”. Icarus 328 (2019).

[3] J. Vago et al. “ESA ExoMars program: The next step in exploring Mars”. SSR 49.7 (2015).

[4] A. C. Vandaele et al. “NOMAD, an Integrated Suite of Three Spectrometers for the ExoMarsTrace Gas Mission: Technical Description, Science Objectives and Expected Performance”. SSR 214.5 (2018).

[5] T. von Clarmann et al. “Retrieval of temperature and tangent altitude pointing from limb emission spectra recorded from space by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)”. JGR: Atmospheres 108.D23 (2003).

[6] Sergio Jiménez-Monferrer et al. “CO2 retrievals in the Mars daylight thermosphere from its 4.3μm limb emission measured by OMEGA/MEx”. Icarus 353 (2021).

[7] Clive D Rodgers. Inverse Methods for Atmospheric Sounding. WORLD SCIENTIFIC, 2000.

[8] Jurado Navarro et al. Retrieval of CO2 and collisional parameters from the MIPAS spectra in the Earth atmosphere. Universidad de Granada, 2016.

[9] M. Luginin et al. “Properties of Water Ice and Dust Particles in the Atmosphere of Mars During the 2018 Global Dust Storm as Inferred From the Atmospheric Chemistry Suite”. JGR: Planets 125.11 (2020).

[10] A. Stcherbinine et al. “Martian Water Ice Clouds During the 2018 Global Dust Storm as Observed by the ACS-MIR Channel Onboard the Trace Gas Orbiter”. JGR: Planets 125.3 (2020).

[11] Michael I Mishchenko et al. Scattering, absorption, and emission of light by small particles. Cambridge university press, 2002.

[12] Pauli Virtanen et al. “SciPy 1.0: Fundamental Algorithms for Scientific Computing in Python”. Nature Methods 17 (2020).

How to cite: stolzenbach, A., López Valverde, M.-A., Brines, A., Modak, A., Funke, B., González-Galindo, F., Thomas, I., Liuzzi, G., Villanueva, G., Luginin, M., and Aoki, S.: Composition and size of Martian aerosols as seen in the IR from solar occultation measurements by NOMAD onboard TGO, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-922, https://doi.org/10.5194/epsc2022-922, 2022.

Introduction: Dust is a high albedo material, which is omnipresent on Mars: both on the surface and suspended in the atmosphere. These micrometer-sized particles modify heat balance while being highly mobile: it is a major contributor to current Martian atmosphere and surface dynamic. Information on dust spatial and time distribution was already provided from numerous orbital and surface studies (e.g., [1,2,3]). However, some characteristics of the dust cycle remain uncertain, which is notably related to the large range of spatial scales of the dust movements: from Recurring Slope Lineae (RSL) to global dust storms, and with important interannual variability ([4,5]). Further global monitoring of dust movements with high spatial sampling and over several years may help improving our Martian dust knowledge. Here we present a new method used to derived near-infrared atmospheric dust optical depth using OMEGA observations acquired between 2004 and 2010.

Data and method: We use the near-infrared (NIR) imaging spectrometer OMEGA [6] onboard Mars Express, which acquired about 8300 observations of the Martian surface over that time range, with a spatial sampling typically close to 1 km.

Firstly, we quantify the prominent 2 µm atmospheric CO₂ absorption band which is sensitive to airborne dust that reduces the atmospheric optical paths of the photons. We have developed a model to predict the CO₂ optical depth under clear atmosphere conditions (notably depends on solar incidence angle, albedo and pressure). This allows to compare observed CO₂ optical depth to these predictions and to derive the difference "Δτ_CO2" (more details in [7]).

Then, we transform this Δτ_CO2 into dust optical depth by a calibration with the visible (VIS) dust optical depth (from 880 nm images) measured by the Mars Exploration Rovers (MER) [2]. Concomitant MER/OMEGA observations are used to characterize the relation between Δτ_CO2 and the ground optical depth (notably depends on incidence angle and albedo). Then, we extrapolated this relation to the whole OMEGA dataset to compute a VIS-NIR dust optical depth "τ_dust".

Results and discussion: We produce latitude/solar longitude diagrams, such as in Figure 1 for the Martian year 28. We observed well-known dust cycle characteristics: low dust optical depth values (<0.5) in the "clear atmosphere period" (solar longitude L_s=0-180°) and medium to high values (>1) during the dusty season (L_s>180°) such as the 2007 global dust storm during L_s=260-310°. We also observed medium-high values at northern and southern latitudes during L_s=220-250° that can correspond to dust storms identified in Hellas and Chryse [8]. Other main investigations were made with thermal-infrared (TIR) data [3,9]. We can notice an overall good agreement between our VIS-NIR study and TIR studies. But there are still differences that we studied by computing the dust optical depth ratio between our VIS-NIR values derived at 2 µm (and converted to 880 nm using MER) and the thermal ones at 9 µm. This ratio distribution reaches a maximum at 2.4, which is in agreement with the value (2.6) considered in [3] and also with the values found locally with MER [2]. This distribution is very large: 2.0 equivalent standard deviation, which may be related to the mean dust particle size variations according to [2] and to potential observational biases of each method (e.g., uncertainties in the vertical distribution of dust).

Figure 1: VIS-NIR dust optical depth (derived from the OMEGA dataset: see text for details) as a function of solar longitude (L_s) and latitude for Martian year 28.

We also produce global seasonal maps of dust optical depth with a spatial coverage typically greater than 50% for most 60° wide intervals in solar longitude. We provide two seasonal maps of Martian year 29 in Figure 2 (L_s=180-240° and 300-360°). Firstly, we can notice some localized high values, such as in 355°E and 55°S on the L_s=180-240° map, that can be associated to a dust storm. Some main dust storm travel routes [8,10] can be identified, such as the Acidalia-Chryse route which is associated to medium-high dust optical depth values in these two maps. Activity is also observed at RSL sites in this area during both periods [11] represented in Figure 2: rapid disappearance events over L_s=180-240° suggesting dust deposition/horizontal dust transport [12], and RSL formation/lengthening over L_s=300-360° which suggest dust removal. This indicates that local surface movements may be related to large-scale atmospheric dust movements occurring at RSL location.

Figure 2: Two seasonal atmospheric VIS-NIR dust optical depth maps of Mars during Martian year 29. Top: L_s=180-240°; bottom: L_s=300-360°.

Conclusion: We have developed a new method to derived a VIS-NIR dust optical depth using near-infrared data (OMEGA). The method relies on CO₂ absorption band at 2 µm and on a calibration procedure that we implemented, based on MER “ground truth” measurements. We constructed latitude/solar longitude diagrams (Figure 1) and global seasonal maps (Figure 2). Overall, our results are in a good agreement with previous thermal-infrared studies, but with some differences noticed by a particular distribution of the dust optical depth ratio between VIS-NIR and thermal-infrared, with a maximum occurrence value of 2.4. Then, preliminary results indicate that large scale atmospheric dust events may be related to local RSL activity occurring in the Chryse-Acidalia area. We will present further comparisons between atmospheric dust and RSL activities at the conference.

Acknowledgments: The OMEGA/MEx data are freely available on the ESA PSA at https://archives.esac.esa.int/psa/#!Table%20View/OMEGA=instrument.

References: [1] Smith M. D. (2004) Icarus, 167, 148-165. [2] Lemmon M. T. et al. (2015) Icarus, 251, 96-111. [3] Montabone L. et al. (2015) Icarus, 251, 65-95. [4] Szwast M. A. et al. (2006) JGR, 111, E11008. [5] Vincendon M. et al. (2019) Icarus, 325, 115-127. [6] Bibring J-P. et al. (2004) ESA Publication Division, 1240, 37-49. [7] Leseigneur Y. et al. (2021), 52nd LPSC, LPI contribution No. 2548, id. 1741. [8] Wang H. et al. (2015) Icarus, 251, 112-127. [9] Smith M. D. (2004) Icarus, 167, 148-165. [10] Battalio M. (2021) Icarus, 354, 114059. [11] Stillman D. E. et al. (2016) Icarus, 265, 125-138. [12] Vincendon M. et al. (2019) Icarus, 325, 115-127.

How to cite: Leseigneur, Y. and Vincendon, M.: Atmospheric Dust monitoring derived from Orbital Near-Infrared Imaging Spectroscopy and Implications for RSL Formation, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1145, https://doi.org/10.5194/epsc2022-1145, 2022.

Abstract
Using a variety of instruments onboard the Perseverance Rover, a substantial amount of data has been collected and analyzed to understand the environment and atmosphere of the landing site, Jezero Crater. A vital component in understanding this unique environment is studying the local and regional variations of water over diurnal and seasonal timescales. We specifically study the variations of water ice in the atmosphere by observing cloud activity over Jezero Crater using data collected by the Navigation Cameras, NavCam, on board the Mars2020 Rover, Perseverance.

Introduction
Water Ice clouds on Mars have been observed for a long time from both the surface and from orbit to understand the role of water in the atmosphere. Using Viking era data, Tamppari (2000, 2003) observed water ice clouds with peak activity seen during the northern spring and summer time. Opportunity Rover acquired images of water ice clouds during the Aphelion Cloud Belt (ACB) season with peak activity seen from Ls 50^o to 115^o (Lemmon et al., 2015). From the past activity, we have seen that between the solar longitude (Ls) of 45^o to 150^o, the Aphelion Cloud Belt (ACB) forms every Mars Year (MY) in the equatorial region (10^oS–30^oN). (Tamppari et al., 2000) (Smith et al., 2004) 

Furthermore, the Surface Stereo Imager (SSI) on-board the Phoenix Lander showed a large variety of cloud types over the course of the 151-sol mission (Moores et al., 2010). The navigation camera, NavCam aboard the Mars Science Laboratory (MSL, Curiosity) rover has observed cloud activity at Gale crater through cloud movies and surveys. The diurnal and seasonal patterns were comparable with previous observations. The peak cloud activities were observed in the morning/afternoon time and around the ACB period. (Kloos et al., 2018) They have also been reported to leave a thermal signature at night on Gale’s surface (Cooper et al. 2021).

NAVCAM data
At Jezero Crater, water ice clouds have been observed through cloud movies and cloud surveys collected using the Perseverance NavCam instrument that collects colour stereo images with a 96ox73o field of view at 0.33 mrad/pixel. (Maki et al., 2020) Compared to the NavCam on Curiosity, the NavCam on Perseverance holds the capability of imaging in colour which may provide advantages in highlighting water ice clouds in the atmosphere. 

Cloud surveys are single images taken facing the horizon, generally twice a week, at various times of the day. Similarly, cloud movies are collected by taking 8 frames of images looking towards the horizon with an interval of 15 seconds, producing a movie. A combination of cloud surveys and movies collected by the mission are used to study water ice clouds.

Data Processing
Various image processing techniques are used on these data sets to emphasize the presence of water ice clouds in the atmosphere. For example, the NavCam Cloud movies can be processed using an imaging technique known as Mean Frame Subtraction (MFS) to enhance cloud features (Campbell et al., 2020) (Moores et al., 2015). This technique takes the average frame of the whole movie and subtracts it from each frame (Moores et al., 2015). This reveals the time-variable component, displaying the cloud movement within the movie. Figure 1 shows an example of raw (left) versus MFS processed frames (right) of a NavCam cloud movie. In addition to these processed images and movies, we have explored techniques such as two-dimensional fast Fourier transforms to recognize patterns in clouds.

Figure 1: Comparison between raw and Mean Frame Subtraction frames. The raw frame (left) only shows faint clouds but when the Mean Frame Subtraction method is applied (right), the cloud features become visible.

We will be presenting the water-ice cloud activity at Jezero Crater with details on various image processing techniques used to determine the characteristics of Martian clouds. The full data set from the start of the Mars2020 mission up to now will be analyzed to determine any seasonal patterns in the cloud activity seen at Jezero. 

Bibliography
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How to cite: Patel, P., Coates, A., Tamppari, L., de la Torre Juárez, M., Lemmon, M., Toledo, D., Wolff, M., Moores, J., Campbell, C., and Brown, A.: Underlining the Image Processing Techniques Used to Analyze Martian Water Ice Clouds Observed at Jezero Crater by the NavCam Instrument on board the Mars2020 Rover, Perseverance., Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-679, https://doi.org/10.5194/epsc2022-679, 2022.

Aeolian sediment transport has been seen to occur on Mars as well as other extraterrestrial environments, generating ripples and dunes as on Earth. The search for terrestrial analogues of planetary bedforms, as well as environmental simulation experiments able to reproduce their formation in planetary conditions, are powerful ways to question our understanding of geomorphological processes towards unusual parameter sets. Here, using sediment transport laboratory experiments performed in a closed-circuit wind tunnel placed in a vacuum chamber, which is operated at extremely low pressures, we show that Martian conditions belong to a previously unexplored saltation regime. The saltation transport wind speed is quantitatively predicted by the state-of-the art models up to a density ratio between grain and air of 4x10⁵, but unexpectedly falls, above this cross-over point, to much lower values than expected. By contrast, impact ripples, whose emergence is continuously observed on the granular bed over the whole pressure range investigated, display characteristic wavelength and propagation velocity essentially independent of the pressure. Testing these findings against existing models suggests that sediment transport at low Reynolds number but high grain to fluid density ratio may be dominated by collective effects associated with grain inertia in the granular collisional layer.

Ref: B. Andreotti, P. Claudin, J.J. Iversen, J.P. Merrison and K.R. Rasmussen, Proc. Natl. Acad. Sci. USA 118, e2012386118 (2021).

How to cite: Claudin, P., Andreotti, B., Iversen, J. J., Merrison, J. P., and Rasmussen, K. R.: A lower-than-expected saltation threshold at Martian pressure and below, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-137, https://doi.org/10.5194/epsc2022-137, 2022.

In eolian events, where large amounts of dust are carried through an atmosphere, strong electric fields can be generated above ground. Electric charge is transmitted via tribocharging during inter-particle collisions which can have a great impact on further particle transport and sedimentation. If different grain sizes, for example, charge differently, this might lead to size dependent particle and charge separation [1]. It could also promote particle lifting [2,3]. This shows, that understanding the charging behavior of particles and aggregates in strong electric fields is important in the context of particle transport in atmospheres. Especially on Mars, any kind of support for particle lifting might be crucial.

We investigate the charging behavior of mm-sized basaltic dust aggregates with the help of microgravity experiments at Bremen drop tower. Our setup consists of a 50 x 50 x 110 mm chamber which we operate in an air environment. The sides of the chamber are copper plates which function as electrodes. At the bottom of the chamber, the sample is placed inside a cylindric aluminum container, which is also coated with basalt dust. The dust grains making up the agglomerates are in the µm size range. The aggregates themselves range from 0.4 – 2.2 mm in diameter.

Before the microgravity phase, we shake the aggregates for 15 minutes in order to electrically charge them. As soon as the sample is ejected into an 8 kV DC field, the aggregates are accelerated towards one of the electrodes. Through this acceleration, we can estimate the charge of the individual agglomerates. This way, we observe initial charges up to 10⁵­ e, both negative and positive without an obvious bias in polarity. Once the aggregates reach an electrode, they either instantly stick to it or bounce off, but eventually cling to the copper plate. Most agglomerates larger than 0.4 mm do, however, recharge while sticking on the electrode until the repelling Coulomb force outweighs the adhesive sticking force. The sticking time is on the order of 0.05 – 0.5 s. The agglomerates charge up to 10⁷ e until they are accelerated to the opposite electrode and recharge again. This charge gained on the electrodes is up to two orders of magnitudes higher than the initial charge. When agglomerates bounce on an electrode, no significant charge is transmitted. The experiments are in agreement with a model where conductive grains on a conductor in an electric field charge, increasing the repulsive force until the different contacts can no longer oppose lifting with their adhesive forces [4].

Our results show that the basaltic dust aggregates are moderately electrically conductive. This presumably is caused by water clinging to the surface and the inside of the agglomerates, making the impact of an electric field on particle transport dependent on the humidity of the ambient atmosphere. In any case, these measurements allow us to quantify the charges and the lifting forces within a given field. If electric fields were present on Mars, electrostatic repulsion might support reducing the threshold friction velocity for saltation.

References:

[1]          K.M. Forward, D.J. Lacks, R.M. Sankaran, 2009, Geophys. Res. Lett.,36, p. L13201
[2]          Renno N. O., Kok J. F., 2008, Space Sci. Rev., 137, 419
[3]          von Holstein-Rathlou C., Merrison J. P., Brædstrup C. F., Nørnberg P., 2012, Icarus, 220, 1
[4]          F. C. Onyeagusi, F. Jungmann, J. Teiser, G. Wurm, (in prep).

How to cite: Onyeagusi, F. C., Jungmann, F., Teiser, J., and Wurm, G.: Lifting Dust Aggregates in Electric Fields, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-209, https://doi.org/10.5194/epsc2022-209, 2022.

Dust in the Martian atmosphere is (under regular conditions) not larger than a few micrometers in diameter.
Liberation through impacts of sand grains during saltation is thought to be one source of this fine dust within 
the atmosphere, as windspeeds usually do not exceed the threshold windspeed needed to pick up the highly 
adhesive smallest particles directly.
We conducted a laboratory experiment to take a closer look at these saltating impacts and the resulting PSD of 
the Ejecta on a microscopic scale: A small number of particles of about 200μm in diameter impacted a 
simulated Martian soil (bimodal Mars Global Simulant). Impacts occurred at flat angles in fine vacuum 
(10^-2 mbar) with an impact speed of ∼ 1 m/s. The ejected dust was captured on adjacent 
microscope slides and its size distribution was analyzed.
We find that the probability for ejection decreases dramatically with decreasing size. However, in spite of 
strong adhesive forces, individual impacts still emit dust of 1μm and less. In fact, the probability 
of ejecting dust of a given size can be characterized by a power law in the decade between 0.5μm 
and 5μm (diameter).

How to cite: Becker, T., Wurm, G., and Teiser, J.: A laboratory study on sand grain impacts and their role in releasing fine dust into the Martian atmosphere, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-13, https://doi.org/10.5194/epsc2022-13, 2022.

The dust cycle dominates Mars's meteorology. Studying the dust injection into the atmosphere is crucial to understanding and modeling the planet's climate. The Mars Environmental Dynamics Analyzer (MEDA) [1], on board the Perseverance rover, is a meteorological station than has been operating on Mars's surface for more than 400 sols [2]. One of the main goals of MEDA is to study the Mars dust cycle, and for this purpose, it includes the Radiation and Dust Sensor (RDS) [3], among other instruments. This instrument contains two different sensing technologies for dust characterization: a CCD camera looking at the sky and a radiometer based on silicon detectors arranged in different orientations. As a result of the RDS field of view, the number of sensors, and low power consumption and data volume, this sensor is capable of detecting and characterizing dust lifting events such as dust devils for extended periods (of hours) and at a high sampling frequency (1 Hz). Moreover, for the cases with multiple RDS detections and wind sensor observations, the trajectory and dust devil geometry can be derived.

In this work, we have estimated for the first 365 sols: i) the number of dust devils formed at Jezero (expressed in number per area and unit of time); ii) the dust devil impact on the irradiance levels on the surface at different wavelength ranges (e.g. UV or 190-1200 nm ranges); iii) the dust devil spatial distribution along the rover traverse; and iv) the dust devil geometry (diameter and altitude) and trajectory for some of the events. For these analyses, we made used of radiative transfer and Monte-Carlo trajectory simulations. We will also discuss the implications of these results on the Mars dust cycle.    

[1] Rodriguez-Manfredi, J. A., et al. (2021). The Mars Environmental Dynamics Analyzer, MEDA. A suite of environmental sensors for the Mars 2020 mission. Space science reviews, 217(3), 1-86.

[2] Newman, C.E. et al. The dynamic atmospheric and aeolian environment of Jezero crater, Mars, Science Advances (in press).

[3] Apestigue, V. et al. Radiation and Dust Sensor for Mars Environmental Dynamic Analyzer Onboard M2020 Rover. Sensors, 22, 2907 (2022). doi:10.3390/s22082907

How to cite: Apestique, V., Toledo, D., and Arruego, I. and the MEDA and ATM team: Dust Devil frequency of occurrence at Jezero crater and radiative effects as derived by MEDA-RDS, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-573, https://doi.org/10.5194/epsc2022-573, 2022.

The Mars 2020 Perseverance rover is developing its mission in Jezero crater [1], a north tropical location that is rich in vortices and dust devils [2]. The MEDA instrument [3] collects atmospheric data at a typical frequency of 1 Hz with several sensors including pressure and winds. It also registers data about atmospheric dust with its set of photodiodes [4]. Together, these data are providing a large set of detections of vortices and dust devils [2, 5] that can be used to investigate the physical properties of the vortices and their effects on the environment though the combination of additional data obtained by MEDA. Here we present a physical characterization of dust devils detected with the pressure data and confirmed as dust devils from the set of photodiodes on MEDA. We show that the combination of pressure, winds and a simple model of drifting vortices [6] can fit the observations of many of these events determining their true central pressure drop, diameter and maximum circulation winds. The quality of the comparisons depend on the varying quality of the wind measurements and is better in short encounters with small vortices than in long encounters with large dust devils. We examine how the vortices characteristics, i.e. their true diameter, minimum distance of the encounter, central pressure drop and maximum wind intensity compare with the detection of dust and its basic inferred abundance and explore the consequences for the efficiency of vortices of different sizes and intensities to raise dust from the Martian surface. We also compare these vortex parameters with environment thermal properties, such as the thermal gradient from the surface and the air, and the thermal perturbations caused by the vortex in a selection of the best observed cases. A comparison with main properties of vortices observed in the different surveys of dust devil activity carried on by the cameras onboard Perseverance will be also presented.

References:

[1] Farley, K.A. et al. Mars2020 Mission Overview, Space Sci. Rev., 216, 142 (2020). Doi: 10.1007/s11214-020-00762-y

[2] Newman, C.E. et al. The dynamic atmospheric and aeolian environment of Jezero crater, Mars, Science Advances (in press).

[3] Rodriguez-Manfredi, J.A. et al. The Mars Environmental Dynamics Analyzer, MEDA. A Suite of Environmental Sensors for the Mars 2020 Mission, Space Science Reviews, 217, 48 (2021), doi:10.1007/s11214-021-00816-9.

[4] Apestigue, V. et al. Radiation and Dust Sensor for Mars Environmental Dynamic Analyzer Onboard M2020 Rover. Sensors, 22, 2907 (2022). doi:10.3390/s22082907

[5] Jackson, B. Vortices and Dust Devils as Observed by the Mars Environmental Dynamics Analyzer Instruments on Board the Mars 2020 Perseverance Rover, The Planetary Science Journal, 3, 20 (2022). Doi: 103847/PSJ/ac4586

[6] Lorenz, R., Heuristic estimation of dust devil vortex parameters and trajectories from single-station meteorological observations: Application to InSight at Mars. Icarus, 271, 326-337 (2016). doi: 10.1016/j.icarus.2016.02.001

How to cite: Hueso, R., del Río-Gaztelurrutia, T., Munguira, A., Sánchez-Lavega, A., Murdoch, N., Newman, C., Lemmon, M., Apéstigue, V., Toledo, D., Arruego, I., Viudez-Moreiras, D., de Vicente-Retortillo, Á., de la Torre-Juarez, M., Lorenz, R., Martínez, G., Rodríguez-Manfredi, J. A., Tamppari, L., Navarro, S., Gómez-Elvira, J., and Harri, A.-M. and the The Mars 2020 ATM team: Physical characterization of dust devils at Jezero crater from Mars2020/MEDA data, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-230, https://doi.org/10.5194/epsc2022-230, 2022.

We have accumulated almost uninterrupted observations of dust from satellites in orbit around Mars for more than 20 years to date. Such a long-term and multi-instrument record can be used to identify dust events, including large-scale dust storms, occurring in the last 13 Martian Years (MY). Using observations from three American instruments operating in the thermal infrared, namely the Thermal Emission Spectrometer (TES, aboard Mars Global Surveyor), the Thermal Emission Imaging System (THEMIS, aboard Mars Odyssey), and the Mars Climate Sounder (MCS, aboard Mars Reconnaissance Orbiter), we have been able to reconstruct diurnal maps of column dust optical depth (CDOD) from mid-summer in MY 24 to the end of MY 35 [1, 2]. These maps are used as input “dust scenario” in the Mars Climate Database (MCD, [3]), among other practical applications. They are publicly available in NetCDF format on a dedicated webpage of the MCD website [4].

The quality of these diurnal CDOD maps also allows the identification of large-scale dust storms (so-called “regional” and “global” storms) and the reconstruction of their main characteristics in space and time, such as the trajectory, area, and average optical depth (see Figures 1 to 3). This work is aimed at 1) building a long-term record of key dust storm characteristics based on satellite observations in the thermal infrared, 2) comparing this record to data derived from satellite observations at visible wavelengths, and 3) producing reliable statistics for Mars science and exploration, leading to statistical large-scale dust storm prediction.