20-EPN2-111: Proton Radiolysis of Astrochemically Relevant Formamide Ices Using A Formal Statistical Experimental Design

Visit by Perry Hailey of the University of Kent (UK) to TA2.11 Atomki Ice Chamber for Astrophysics / Astrochemistry (ICA) (Hungary).
Dates of visit: 02-22 May 2022

Report Summary:

Formamide (NH₂CHO) is of astrobiological interest as it has been identified as a potential precursor to a wide variety of organic compounds essential to life, and many biochemical studies propose it is likely to play a crucial role in the context of the origin of life.  Formamide contains an amide functional group which is the principal building block necessary to form chains of amino acids and proteins. Furthermore, it has been identified as a key precursor of a large variety of prebiotic molecules and in the presence of an energy source, it promotes the synthesis of adenine, guanine, cytosine, and uracil, which are the four nucleobases of ribonucleic acid or RNA; it is also a precursor of carboxylic acids, amino acids, and sugars.  In summary, the chemical versatility of formamide can lead, under favorable conditions, to the synthesis of many molecules that are key constituents of living organisms.  Several studies report the prebiotic synthesis of nucleobases from formamide under relatively warm conditions (i.e. near or above room temperature), there are no reports on the formation of nucleobases from formamide in interstellar ices through the combination of irradiation at astrophysically relevant low temperatures and subsequent thermal processes.  A few laboratory based studies have explored formamide irradiation although with in a largely non-systematic manner, typically employing a change One Factor At a Time (OFAT) approach.  Additionally, scant attention has been paid to the refractory components from the irradiation which would likely reveal the complex chemistry that emerges.

To investigate the role of cosmic ray induced chemistry, the Atomki Ice Chamber for Astrophysics / Astrochemistry (ICA) was used and ice analogues were prepared in situ by depositing gases and Formamide onto ZnSe substrates at 20 K, where they were monitored in the solid-phase by Fourier Transform Infrared (FTIR) Spectroscopy and QMS monitoring of the gaseous emissions.  TPD studies will also be performed from 20 through to 200K and both QMS and FTIR data captured on a temporal basis to allow for univariate and multivariate post data analysis.  Refractory components were also be retained for post chiral/achiral analysis.

22-EPN3-048: Evaluation of the initial 92Nb abundance in the inner Solar System

Visit by Makiko Haba, Tokyo Institute of Technology (Japan) to TA2.14 ETH Zurich Geo- and Cosmochemistry Isotope Facility (Switzerland).
Dates of visit: 02-15 August 2023

Report Summary: Evaluation of the heterogeneous distribution of short-lived 92Nb in the protoplanetary disk is mandatory to utilize the ⁹² Nb-⁹²Zr chronometer for dating planetary materials. A higher initial ⁹²Nb/⁹³Nb ratio has been reported for one meteorite that originate from the outer Solar System compared to meteorites from asteroid Vesta, which formed in the inner Solar System. The initial ⁹²Nb/⁹³Nb ratios determined at high precision from various types of meteorites are needed to comprehend the initial distribution of ⁹²Nb in the early Solar System. To evaluate the initial ⁹²Nb/⁹³Nb ratio in the inner Solar System, we conducted Zr isotopic measurements of rutiles separated from the Miles iron meteorite (IIE), whose parent body is considered to have formed inside Vesta in the protoplanetary disk.

During the Europlanet TA visit, the Zr isotopic compositions of five rutile fractions were analysed using a Neptune Plus MC-ICPMS. These rutile fractions with large variations in Nb/Zr ratios yielded ε⁹² Zr values from 0.19 ± 0.28 to 5.27 ± 0.21. The Nb-Zr data form a single, well defined isochron yielding a ⁹²Nb/⁹³Nb Nb ratio of (1.10 ± 0.07) × 10^-5 at the time of rutile formation. Using the absolute age of the Miles iron meteorite (4542.3 ± 4.0 Ma, Kirby et al., 2022) yields an ⁹²Nb/⁹³Nb ratio of (1.76 ± 0.12) × 10^-5 at CAI formation. This is consistent with the initial ⁹²Nb/⁹³Nb ratio in Vesta formation region ((1.66 ± 0.10) × 10^-5), suggesting that the initial ⁹²Nb/⁹³Nb ratio was homogeneous in the inner Solar System.

22-EPN3-30: An Isotopic Inventory of Mars Analogue Environments

Visit by Michael Christopher Macey of the Open University (UK), to TA2 Facility 17 – Isotoptech Stable/Clumped Isotopes Laboratory (Hungary).
Dates of visit: 06-10 November 2023.

Report Summary: This study analysed the carbon, oxygen, sulfur, and nitrogen isotope profiles in physiochemically distinct analogue environments to establish how the viability of biologically induced isotope fractionation as a candidate biosignature. The analysis was performed on sediment samples collected from analogue environments proposed as appropriate analogues for Noachian-Hesperian waters requires environments (e.g., highly saline and sulfurous). Specifically, these environments were the Salt flats of Western Sahara, a hypersaline environment that contains sulfurous sediments below thick halite layers, the high-altitude lakes of the Argentinian Andes, which possess a chemistry like dilute, modelled martian water chemistries and are impacted by a low atmospheric pressure and large diurnal fluxes in temperature and UV, the salt pans of the Makadikadi basin, and hypersaline lakes in Spain.

The analysis identified varied isotopic signatures across locations suggestive of diverse environmental conditions in terms of their microbial community, geology and inputs to the environment. Key differences include: Positive ³⁴S ad low ¹³C values in the Botswanan sediments, aligning with the detection of oxic conditions, while negative values in Argentinian and Saharan samples indicate a contribution of dissimilatory sulfur metabolisms. Variation in ¹⁵N values between environments highlight previously detected variation in the presence and abundance of nitrogen-dependent metabolisms. The ¹⁸O values also strongly support the input of glacial water into the Argentinian lakes. The synthesis of this isotopic analysis with geochemical and microbiological datasets from these Mars analogue environments stands to provide crucial insight into their role as potential biosignatures.

22-EPN3-064: Investigating Oxygen Isotopes within Ca-Al-rich inclusions (CAIs) and Compound-Chondrule-CAI (CCCAIs) Populations within CM chondrites

Visit by Pierre-Etienne Martin and Luke Daly of the University of Glasgow (UK) to TA2.9 Ion Probe Facility (IPF), CRPG (France)
Dates of visit: 24-28 April 2023

Report Summary: Compound-chondrule-Calcium-Aluminium-rich Inclusions (CCCAIs) are rare occurrences within carbonaceous chondrites. They have been reported sporadically within most major groups (CO, CV, and CH) and only described four times within CM (Mighei-like) carbonaceous chondrites of various degrees of aqueous alteration, such as Aguas Zarcas (CM2; Martin & Lee, 2021) and Paris (CM2.7; Rubin, 2015). These objects have been described as CAIs enclosing chondrules or as chondrules enclosing CAIs. The existence of CCCAIs suggests that chondrules and CAIs interacted within high particle density environments in the protoplanetary disk prior to their incorporation into their mutual parent bodies.

In this study, we investigated two such objects within the Aguas Zarcas meteorite using oxygen isotope
analysis in order to characterize the CAI and chondrule components of the CCCAIs in comparison with CAIs and chondrules within the rest of the two Aguas Zarcas samples. Results show that the CAI and chondrule components of CCCAIs originate from the same O isotope reservoirs as their regular counterparts, suggesting that no isotopic exchange occurred between the two types of components, and that the components originate from the same O isotope reservoirs as the CAIs and chondrules of the meteorite breccia. An exception is the ‘Cicero’s’ chondrule part, which has a very primitive O isotope composition similar Amoeboid Olivine Aggregate (AOA). Due to the very primitive O isotope composition of AOAs, their formation is thought to have occurred in a near-solar environment. Further evidence is needed, but the existence of these objects can better our understanding of the evolution of the protoplanetary disk and provide a new way to study the chondrule forming environment(s).

22-EPN3-020: Implantation of Oxygen Ions in Titan’s Aerosol Analogues

Visit by Veronique Vuitton and Filip Matuszewski of Institut de Planetologie et d’Astrophysique de Grenoble (France) to to TA2.12 Atomki-Queen’s University Ice Laboratory for Astrochemistry (Hungary).
Dates of visit: 18-22 March 2024

Report Summary: In this TNA visit, we irradiated adenine, an aromatic molecule rich in nitrogen, with low energy oxygen ions. Our general objective was to investigate the effect on the spectral properties and composition of the samples and on the chemical composition of the molecules sputtered in the gas phase.

Films of a few hundred nanometers were prepared using the sublimation/condensation reactor installed on Atomki QUeens Ice Chamber for Laboratory Astrochemistry (AQUIILA). Adenine is commercially available as a powder and was vaporized under low pressure to condense back on MgF2 windows. We irradiated our samples with 10-20 keV OH_x⁺ ion beams generated by the Electron Cyclotron Resonance Ion Source (ECRIS).

During the irradiation, the spectral properties of the irradiated samples were tracked in situ by FTIR spectroscopy. The products released during the irradiation were tracked with the residual gas analyzer attached to the AQUIILA chamber.

Ex situ analyses of the irradiated samples are also planned to determine their chemical evolution, especially their degree of oxygenation. The elemental and isotopic compositions will be determined by isotope ratio mass spectrometry (ir-MS), with the main objective to obtain their O/C ratio. The molecular composition of the samples will be obtained through very high-resolution mass spectrometry (HRMS).

22-EPN3-010: The Cosmic Dust Flux Over Geological Time – How Extraterrestrial Signals Become Preserved in Earth’s Marine Rock Record

Visit by Martin D. Suttle of the Open University (UK) to TA2.10 Stable, Rare Gas and Radiogenic Isotope Facility at CRPG (France). Isabelle Mattia (Imperial College London) also took part in the visit, supported through other funding.
Dates of visit: 18 – 27 October 2023

Report Summary:

Fossil micrometeorites (MMs) recovered from sedimentary rocks are mostly <2mm-sized I-type cosmic spherules (CSs): iron-rich cosmic particles that have experienced high degrees of melting and oxidation during atmospheric entry. Since extraterrestrial ³He is implanted into cosmic dust by solar and cosmic rays in interplanetary space, fossil I-types could play a significant role as carriers of ³He in sedimentary archives. This project aimed to test this hypothesis by systematically examining the ³He/⁴He ratios of various types of MMs at different stages of preservation.

Measurements of He isotopes using the Helix SFT mass-spectrometer at CRPG, Nancy revealed variable 3He/4He values, with only 8 of the 36 measurements yielding results above the solar energetic particle (SEP) ratio of 2.17E-04  – most of these were, expectedly, scoriaceous Antarctic MMs which experienced the least atmospheric heating. Two urban CSs and a fossil I-type were also enriched in 3He, suggesting preservation of some implanted nobles gases, although rare, is possible for particles that have experienced high degrees of entry heating and/or alteration during diagenesis. A host chalk enriched in fossil I-types returned a low ratio of 1.00E-06, which could imply ³He may be preferentially removed by secondary fluids peculating within the lithifying sediment, or the source of cosmic dust was not sufficiently saturated in extraterrestrial 3He.The main conclusions from this work are that the ³He signal and the abundance of fossil (I-type) micrometeorites in Earth’s sedimentary rocks are uncoupled. This implies that these two proxies (³He and fossil micrometeorite abundance) record separate size distributions of the extraterrestrial dust flux.

22-EPN3-113: Isotopic constraints on deformation of olivine: a preliminary study on mantle peridotites from Mt. Melbourne, northern Victoria Land, Antarctica

Visit by Daeyeong Kim and Jung Hun Seo of the Korea Polar Research Institute (KOPRI, Korea) to TA2.10 Stable, Rare Gas and Radiogenic Isotope Facility at CRPG (France).
Dates of visit: 17 August – 06 September 2023

Report Summary: Microstructures of olivine-rich rocks record tectonic events in mantle, due to their diverse slip systems associated with the various deformation conditions. There have been, however, no time constraints on the slip systems that generate the microstructures of olivine. This study first investigates the temporal relationship of various microstructures of olivine based on the Re-Os geochronology of included sulphides. Mantle xenoliths of one lherzolite and two harzburgites were collected near Mt. Melbourne, northern Victoria Land, Antarctica, which suffered several tectonic events during the Proterozoic and Phanerozoic eons. Sulphide grains are texturally associated with olivine deformation fabrics in mantle rocks. The Re-Os isotopes of the 18 sulphide grains collected from the mantle xenoliths were analysed by using multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and negative-ion thermal ionization mass spectrometry (TIMS) at CRPG Nancy, France.

The measured Os quantities are 0.9–4789.3 pg and Re quantities are 4.3–7.0 pg in the sulphides. ¹⁸⁷Os/¹⁸⁸Os in the sulphide are 0.1250–0.1298 for J04-A, 0.1130–0.1185 and 0.1286 for J04-B, and 0.1203–0.1216 for J04-D1. The corresponding depleted mantle ages (T_RD) are calculated to be 0.26–0.63 Ga for J04-A, 1.5–2.3 and 0.14 Ga for J04-B, and 1.1–1.3 Ga for J04-D1. The ages correspond to the tectonic evolution of suturing, subducting, and rifting events of the studied area, implying that the various structural events preserved in the mantle xenoliths can be temporally constrained by the sulphide Re-Os geochronology.

22-EPN3-025: Isotope Geochemistry Traces Magma–Shale Interaction

Visit by Manfredo Capriolo, University of Oslo (Norway), to TA2.10 Stable, Rare Gas and Radiogenic Isotope Facility at CRPG (France).
Dates of visit: 17 – 28 April 2023

Report Summary: The research project aims to constrain and quantify magma–shale interaction via rhenium-osmium isotope analyses of whole rock samples from different geological settings in the Oslo Rift (about 300 Ma). Magma–shale interaction can produce massive amounts of greenhouse gases when magmas are injected into sedimentary basins, with potential implications for sulphur sequestration as sulphides. Here, 8 magmatic rock samples (of both intrusive and effusive origin) and 2 host shales were analysed in the laboratories of the Stable Rare Gas and Radiogenic Isotope Facility (CRPG, Nancy, France).

Among the investigated magmatic ones, 7 rock samples are alkali basalt sills with variableextents of hydrothermal overprint, and 1 rock sample is an evolved lava. The latter has a very low (< 5 ppt) Os concentration, making its magmatic Os isotope ratio prone to overprinting by crustal assimilation. The 7 alkali basalt sills display ¹⁸⁷Os/¹⁸⁸Os_299Ma values ranging from 0.14 to 1.15, reflecting different (from negligible to strong) degrees of shale contamination. Interestingly, the 2 host shales of Cambrian age display ¹⁸⁷Os/¹⁸⁸Os_299Ma values of 1.12 and 1.42. The rhenium-osmium isotope data from this research project indicate that magma–shale interaction via shallow magmatic intrusions in sedimentary basins can vary in intensity, implying a different extent of thermogenic degassing. These results improve the understanding of degassing scenarios from past events, open new perspective on the comparison with present-day atmospheric changes, and suggest interesting implications for economic resources, such as hydrocarbon reservoirs or sulphide ore deposits.

22-EPN3-097: Characterising the Low-Temperature Spectral Properties of Lunar and Martian Analogues

Visit by Merve Yeşilbaş and Lucas Demaret of Umeå University (Sweden) to TA2.8 CSS (Cold Surfaces Spectroscopy) at IPAG (France).
Dates of visit: 23 October – 03 November 2023

Report Summary: Characterising the spectral properties of minerals and analogue materials under low-temperature vacuum environments enables a better understanding of how the spectral features of these materials would appear on the Moon and other planetary surfaces. This study involved measurement of reflectance spectra from 0.4 to 4.2 μm under low-temperature and vacuum conditions at the University of Grenoble Alpes CSS Facility of several analogue soils and minerals for the Moon and Mars. Samples investigated include enstatite, two lunar soil analogues, ferrihydrite, gypsum, and iron sulphates.

The experiments performed at the CSS revealed surprising changes in spectral features under
reduced temperature conditions for some samples. The band centres in spectra of the iron sulphate mineral szomolnokite shifted to longer wavelengths for some features as the temperature was decreased, and to shorter wavelengths for other features and remained the same for some features. We also documented changes in the hydration bands under vacuum and decreasing temperature conditions, which are important to understand for remote sensing on planetary surfaces. This short visit at the University of Grenoble Alpes supported by the Europlanet 2024 RI program is opening up a wide array of new collaborations with new experiments to understand the spectral properties of analogue minerals and soils for the Moon and Mars.

22-EPN3-083: SHOCKchar: Charring of Wood Induced by a Shock Wave during a Hypervelocity Impact

Visit by Anna Losiak, Institute of Geological Sciences Polish Academy of Sciences (Poland) to TA2.7 Light Gas Gun Laboratory, University of Kent (UK)
Dates of visit: 23 November – 01 December 2023

Report summary: Proximal ejecta blankets of very small (<200 m in diameter) impact craters contain fragments of charcoal (Losiak et al. 2022). They were found in Campo del Cielo, Whitecourt, Kaali Main, Kaali 2/8, and Morasko, as well as in two suspected craters: Sobolev and Ilumetsa. Those charcoals can be used to: precisely and accurately date impact structures, determine environmental effects of impact of small asteroids and, potentially in the future, better understand the energy distribution during formation of very small impact craters or identify impact origin of yet unknown structures. The formation mechanism of impact charcoals is unknown. The first hypothesis, based on field observations, assumes impact charcoals were formed by burial of branches in locally warm ejecta, resembling charcoals buried within pyroclastic flows. An alternative explanation, based on numerical modelling (Svetsov and Shuvalov 2020), is that charcoals are formed by shock-wave propagation through trees. THE AIM of this project is to test if impact charcoals can be formed by a shock wave passage, and to characterize the properties of resulting charcoals. The Light Gas Gun laboratory at the University of Kent was selected to conduct the experiment because it is one of very few in the world that allows to reach >5km/s velocities as well as perform experiments at atmospheric pressure.

During the Europlanet TA visit we have performed 8 experiments. We have varied the following parameters: 1) velocity: 5 / 3 / 2 km/s, 2) wood dryness: fresh / dried, 3) atmospheric pressure: 1 bar / ~0 bar.

The initial evaluation of the results suggests that wood hit at 5 km/s results in production of a very small amount of thermally processed material. It is not clear if this material has similar properties to impact charcoals. The full analysis is ongoing

20-EPN-004: Spectroscopy of Shock Processed Planetary Analogues Mimicking Impact Events on the Surface of Mercury

Visit by Arijit Roy and Wafikul Khan of the Physical Research Laboratory, Ahmedabad (India) to TA2 Facility 5 – DLR Planetary Spectroscopy Laboratory (Germany).
Dates of visit: 09-13 October 2023

Report Summary: The surface of the airless Solar System bodies has been modified both physically as well as chemically by the impacts induced shock processing. Planetary scientist uses multispectral
remote sensing technique to understand the surface chemistry of these airless planetary bodies. Different spectral ranges reveal distinct descriptions and characteristics of the observed planetary surface. Like, VIS-IR spectroscopy focused on a rocky planet provides insights into the distribution of iron (Fe) and titanium (Ti)-rich minerals, spanning both its igneous and sedimentary phases. In contrast, IR spectroscopy exposes the abundance of silicon-oxygen (Si-O) bonds, offering a glimpse into the bulk mineralogy of the surface. This leaded to the better understanding of the abundance of minerals and their distribution on the different planetary surfaces. Olivine is often observed on the surface of different Solar System objects such as Venus, Mercury, Our Moon, and Asteroid Vesta. In the case of Mercury
impacts allowed olivine to mixed with other abundant sulphides molecules and further processed by shock wave which induced a physico chemical changes leaded to a change in the spectral signature of the Mercury surface.

To address this issue we studied shock processing (5.6 M) of the olivine (dunite) with sulphur, where the mixture was processed at a temperature ~ 7300 K, for 2ms. The shock processed samples later analysed using PSL, DLR’s bi directional reflection spectroscopy set up from UV to FIR wavelength range.Results from this work will help the planetary science community to build a spectral library for the future planetary missions.

22-EPN3-046: Integrated Spectroscopic Study of Apollo 16 Sample and Anorthositic Lunar Meteorite

Visit by Prateek Tripathi, Indian Institute of Technology, Roorkee (India) to TA2 Facility 5 – DLR Planetary Spectroscopy Laboratory (Germany).
Dates of visit: 10-17 December 2023

Report Summary: The objective was to characterise 15 lunar minerals, the Apollo 16 sample, and the Tissertiline lunar meteorite using integrated spectroscopy with the Bruker Vertex80V FTIR instruments at the Planetary Spectroscopy Laboratory (PSL). The minerals studied included pigeonite, augite, ilmenite, orthopyroxenes, olivine, anorthite, and bytownite, with grain sizes ranging from 25-125 μm. Additionally, Apollo 16 sample 62231.44, collected from the rim of Buster Crater and highly mature, was included in the analysis. The methodologies employed integrated bidirectional reflectance spectroscopy in the visible (VIS) and near-infrared (NIR) ranges at 30° and 45° angles, separate hemispherical measurements in VIS and NIR, and emission spectroscopy at temperatures of 70°C, 100°C, and 130°C over the mid-infrared range. The spectral range covered was 0.2 – 150 μm, with a resolution ranging from 0.1 – 8 cm⁻¹. In total, 204 spectra were acquired in ten days of visit, including standards (endmembers/lunar minerals), the Apollo 16 sample, the lunar meteorite, and a black body.

Bidirectional measurements yielded 102 spectra (VIS and NIR separately), hemispherical measurements provided separate VIS and NIR spectra totaling 51, and emissivity measurements contributed 51 thermal emission spectra. This comprehensive methodology allowed for the observation of the effects of temperature and grain size on spectral properties. This integrated optical through thermal spectroscopy approach successfully characterises lunar sample and results in a spectral library that will aid in the interpretation of future lunar mission data for composition identification and resource potential
assessment.

22-EPN3-068: Vacuum Heating Effects on Spectroscopic Properties of Carbonaceous Chondrite Meteorites

Visit by Edward Cloutis and Cain Kiddell, University of Winnipeg (Canada), to TA2 Facility 5 – DLR Planetary Spectroscopy Laboratory (Germany).
Dates of visit: 10-17 December 2023

Report Summary: This project was designed to investigate how conditions that may have affected dark carbonaceous asteroids affect our ability to detect and characterise them. We specifically investigated how exposure of carbonaceous meteorites (which are presumed to derive from carbonaceous asteroids) to the vacuum of space, as well as to heating, affect their spectral reflectance properties. Heating of carbonaceous asteroids may occur during their accretion and decay of radioactive elements, or from close passes to the Sun. We studied a number of different classes of carbonaceous meteorites of low petrologic grade, and will compare them to similar meteorites that show evidence of heating.

We found that vacuum exposure has its greatest effect on the depth and shape of the 3 micron-region water absorption band, while the 2.7 micron region absorption feature, associated with hydroxyl (OH) was largely unaffected.Heating led to a number of spectral changes which we continue to investigate, however preliminary results indicate that heating can affect absorption bands associated with iron. We have also found that the changes in spectral reflectance properties are a function of heating temperature. This results should enable us to constrain the temperatures to which carbonaceous asteroids have been exposed, and provide insights into conditions that prevailed in the early Solar System.

20-EPN2-075: Emissivity Measurements of Proposed Source Minerals for Venus Anomalous Regions

Visit by Erika Kohler, NASA Goddard Space Flight Centre (UK), to TA2 Facility 5 – DLR Planetary Spectroscopy Laboratory (Germany).
Dates of visit: 1-15 December 2022

Report Summary: This study directly measured the emissivities of four Venus-mineral analogues at Venus relevant temperatures and reflectivity spectra pre- and post- heating. Mission and ground-based observations of Venus show several anomalous regions related to elevation, but the variations are unknown to be compositional or morphological in nature. The comparison of emissivity measurements from candidate minerals at Venus surface conditions and reflectivity measurements will demonstrate whether mineralogical composition can be identified in future Venus missions and will constrain the source of the Venus highland radar anomalies. The results of this study will maximise the return of previous and future Venus missions that take surface measurements by contributing to the database of Venus analogues being compiled at the Planetary Spectroscopy Laboratory.

20-EPN2-094: Miniature Wind Vanes on Mars – Extracting Wind Flow Properties From Close-up Images of Sand Grains

Visit by Sebastiaan de Vet and Andreas Zafiropoulosof TU Delft (Netherlands) to TA2.4 Planetary Environment Facilities (PEF), AU (Denmark)
Dates of visit: 22-26 January 2024

Report summary: Aeolian sediments are ubiquitous at the surface of Mars where they are found in active sand dunes and lithified aeolian outcrops. These features form a geological record of past and present interactions between the surface and atmosphere of an evolving planet. A deeper understanding of their formation and context can be obtained by studying these deposits at the grain-scale level. From terrestrial studies, we known that airborne orientation of non-spherical grains due to long-axis streamlining to the wind flow is considered to occur almost instantaneously after entrainment grains by saltation. Grain orientation in sediment fabrics therefore harbours valuable information on near-surface wind flow and particle mobility. A key focus of this project was to establish how atmospheric pressure and above-threshold wind conditions modulate the observed grain orientation signal. Well-rounded aeolian sand for the wind tunnel experiments was collected from the active drift sand geotope at ‘Bedafse Bergen’, located in SE Netherlands.

At the Aarhus Wind Tunnel Facility, we performed several experiments under various atmospheric pressures from ambient sea-level conditions to Mars-analogue pressures. Close-up images were obtained from the sediment fabric after various runs at 120% and 150% above threshold conditions. A date pipeline has been developed and is being refined for processing of imagery and quantifying the grain orientation to ultimately disentangle effects of airborne streamlining of grains and impact randomisation at various wind speeds and atmospheric pressures.

22-EPN3-073: Emergence of Ice Ripples by Sublimation at Various Wind Velocities and Air Pressure

Visit by Sabrina Carpy of the Laboratoire de Planétologie et Géosciences (France) and Philippe Claudin of the Laboratoire de Physique et Mécanique des Milieux Hétérogènes (France), to TA2.4 Planetary Environment Facilities (PEF), AU (Denmark)
Dates of visit: 04-08 March 2024

Report summary: Sublimation waves are the result of the sublimation of icy substrates under turbulent winds. They are expected to be found on many planetary surfaces with volatile ices in contact with an atmosphere. They are periodic, linear and transverse bedforms of different scales (centimeter to decameter) depending on their dry windy environment [Bordiec et al, 2020]. Apart from the BIA’s [Weller, 1969; Mellor and Swithinbank, 1989; Bintanja et al, 2001] and on the walls of ice caves [Curl, 1966], very few field measurements have been collected on sublimation waves. There is no extensive morphological and kinetic data of the development of these bedforms and there are no systematic measurements of the bedform’s wavelength change when continuously varying the wind velocity and fluid viscosity. This is why we have performed a series of experiments in the AWTS-II on carbon dioxide ice under a dry air atmosphere.

After initial difficulties with the ice slab creation and surface conditions, we managed to track the evolution of the substrate height throughout the sublimation phase using laser profilometry. We observed emergent morphologies that could be traces of the linear instability, but whether they correspond to the expected sublimation waves remains to be confirmed by detailed data analysis. Also, an unforeseen phenomenon was observed where transverse waves of frost on leading edges of the ice slab would migrate downstream as the aerodynamic forces on the growing frost would break off flakes. We are developing a model to link this frost coverage to the local friction velocity distribution.

22-EPN3-095: Behaviour of Saline Liquid Droplets in Wind Tunnel Conditions Relevant to the Plumes of Enceladus

Visit by Mark Fox-Powell of the Open University (UK), to TA2.4 Planetary Environment Facilities (PEF), AU (Denmark)
Dates of visit: 19-23 February 2024

Report summary:

The main aim of this project was to investigate the freezing of droplets of saline water injected at high velocity into low pressure conditions, in order to better understand the formation history of salt-rich ice grains encountered by Cassini in the plumes of Saturn’s moon Enceladus. Our objectives were to (1) investigate freezing times of sub-millimetric droplets under pressures representative of the subsurface icy vents at Enceladus; (2) investigate the tendency for ice grains to fragment into smaller grains on impact with solid surfaces; and (3) identify the effects of dissolved salts on both factors. Experiments were conducted in the Aarhus large wind tunnel. Liquids were sprayed into a range of pressures spanning 0.1 – 6 mbar. Spray droplets were imaged with a high-speed camera as they impacted an aluminium target plate, and velocity distributions of droplets were recorded using a laser doppler velocimeter. Real-time observations indicated a strong pressure dependence on freezing times, with droplets at the lowest pressures freezing in less than one second. We observed that the presence of salts enabled droplets to remain liquid longer at lower pressures. In ongoing work, we are analysing high speed footage to quantify the proportions of frozen vs. liquid droplet impacts, and fragmenting vs. non-fragmenting frozen grains, and how these proportions vary across all experiments. These data will allow us to predict likely freezing behaviour of similar droplets in the Enceladus plumes, leading to new understanding of the processes controlling ice grain formation at Enceladus.

22-EPN3-099: Formation of Impact Ripples Induced by Different Flow Rates Under Martian Pressure and Temperature

Visit by Aurore Collet and Sabrina Carpy of the Laboratoire de Planétologie et Géosciences (France), to TA2.4 Planetary Environment Facilities (PEF), AU (Denmark)
Dates of visit: 22 May – 2 June 2023

Report summary: The conditions for the formation of aeolian ripples depend on the surface characteristics (particle flux, surface roughness, nature of the substrate) and the atmosphere (pressure, temperature, viscosity). The understanding of their formation mechanisms is a real challenge to characterise the interaction between the atmosphere and the substrate of different planetary bodies. Constraining the mechanisms would also allow to go back to past information as on Mars where the atmosphere was not as tenuous as today (Mischna, Lee, et Richardson 2012). A method to link their morphological characteristics (wavelength, amplitude) to the physical characteristics (pressure, temperature, viscosity, particle flux) and verify the associated flow regime (transition, equilibrium) (Selmani et al. 2018) is to use scaling law.

There is currently a significant lack of experimental data to understand the influence of the different physical parameters on the initial formation mechanism and the development of the ripples. On Mars, the formation of ripples under a tenuous atmosphere is still poorly constrained, despite that recent works have attempted to tackle this question (Lapotre et al. 2016; Sullivan et al. 2020). The study of the variation of the flow velocity on a given material (silica sand), can be experimented in a wind tunnel under a Martian atmosphere to understand the formation and the development of the aeolian ripples. A pioneer study in the Martian Chamber formed aeolian ripples with a quartz grain size of 125 μm (Andreotti et al. 2021) but natural ripples generally have a distributed grain size as on Mars where aeolian ripples of centimeter-scale wavelength have been detected on an active dune, with a grain size range of 45 – 500 μm (Ehlmann et al. 2017). Moreover, numerical modelling indicates a link between ripple wavelength, grain flow and the erosion rate of the system (Lester et al. 2022). The interaction between flow velocity, wavelength and erosion rate can be studied in space and time using photogrammetry.

20-EPN2-123: Controls on the Resuspension of Dusts of Different Mineral Composition in Air Flows

Visit by Merren Jones and Steve Covey-Crump of the University of Manchester (UK), to TA2.4 Planetary Environment Facilities (PEF), AU (Denmark)
Dates of visit: 11-15 September 2023

Report summary: Mineral dusts in the atmosphere cause a wide variety of damage to aircraft engines resulting in significant economic cost to the engine manufacturers and airline operators. The nature of damage is dependent on the mineralogy of the dust, and so there is currently a major drive to understand the controls on the composition of atmospheric dusts. We are currently planning a field campaign in central Australia to sample airborne sands and dusts together with surficial deposits, and the present study was designed to inform our sampling strategy and to help constrain the interpretation of our anticipated findings.

We performed wind tunnel experiments to examine detachment thresholds of seven minerals with different density, grain shape, and surface properties. The particle size variation (50-500 μm) of the detachment threshold is well-described by existing semi-empirical models but highlights the need to incorporate shape and adhesion properties into these models. In a further set of experiments, we used a new suction sampler to collect sand and dust particles in transport through the full depth of the flow (175 mm) to examine dust emission from the surface of a sand bed under conditions where the sand particles are saltating, and vertical particle size and compositional sorting developed within and above the saltating layer of a polymineralic sand. Provisional results show a good correlation between collected sample mass and mass-flux estimated from a laser opacity system throughout the depth of flow, and show strong vertical particle size and compositional sorting.