Report Summary: This project is devoted to investigate geo- and biosignatures that can be preserved in mineral assemblages formed in extreme aqueous terrestrial environments. Environments such as subaerial hot springs that could had existed on early Mars, and cold-seep marine environments that can develop in icy-moon oceans are particularly interesting for astrobiology. In order to achieve this goal, we use information obtained by Raman spectroscopy and SEM/EDX microscopy.
Raman spectroscopy is a recently incorporated analytical technique in the payload of several space missions: SHERLOC@Perseverance, Supercam@Perseverance, RLS@ExoMars and RAX@MMX. It is based on the scattering effect generated by the interaction of photons with the electron density of the chemical bond of a molecule. The position and width of the Raman bands give information on the structure, chemical and isotopic composition and crystallinity of mineral. Studying changes in Raman frequencies allows to evaluate the biological or inorganic origin of the sample. This methodology is relevant for the in-situ identification of geo- and bio-signatures in soil/rock samples collected during space missions.
Several bio-mediated minerals sampled from several hydrothermal and cold-seep areas were characterised by micro-Raman spectroscopy coupled with scanning electron microscopy (SEM/EDX). Obtained Raman spectrum was correlated with its texture in order to identify patterns that would allow us to assess the biological or inorganic origin. We observed Raman band shifting and width changes. These results should be complemented by further experimental work to determine the involvement of bio-mediation processes.
The main goals of the 2023 visit were to study the electron impact emission cross sections, spectral features, and dissociation thresholds of CS2 gas. The products of CS2 – atomic sulfur and its ions, CS, excited CS2, and CS2+ – make CS2 a rich target of inquiry. Further, the products CS and atomic S are routinely observed in near-nucleus observations of comets (see e.g. discussion in Noonan et al. 2023). Measurements of sulfur abundances in comets show discrepancies between remote and in-situ observations, and improved electron-impact data for CS2 may help resolve this discrepancy. The present experiments are part of a long-term campaign to understand diagnostic electron-impact driven emission and ionization of diatomic/polyatomic molecules in cometary atmospheres. We expect these data will provide valuable insights in one of our ongoing projects to investigate sulfur abundances through analyses of 100+ archived comet observations. In the first week of our visit to the EIF lab, we measured the electron-impact spectrum of CS2 gas at various electron energies between 0 – 100 eV, with energies chosen based on known thresholds for CS, CS2+, and atomic fragment production. During this time, we also began developing an emission model for CS in order to simplify the future analyses of these data. In the second week of the visit, higher-resolution spectra and several cross sections were measured in order to begin comparisons to existing literature. We also identified, for the first time, the emissions of atomic fragments (S I, S II) in the near-infrared red-ward of 600 nm.
Report Summary: Fifteen high-pressure experiments on the PISL end-loaded piston cylinder press were performed at 1 GPa and 1873 K to systematically investigate the effects of Cu and Ni on metal- and sulfide-silicate partitioning of highly siderophile elements (HSE) Pd, Ru, Pt and Ir. Run times at peak conditions varied around 60-90 minutes. The starting compositions consisted of silicate, sulfide and metal powders with added metallic Si. The experimental run products consist of well-segregated metallic and sulfide blobs in a silicate glass. The addition of metallic Si and the initial reduction of the experiments result in the suppression of nugget formation. The glass does contain minute specks typical of S- saturated silicate melts – subsequent LA-ICP-MS measurements of the run products show that these specks do not contain HSE, as initially hypothesized. Electron microprobe and LA-ICP-MS analyses further show that the experimental run products are homogeneous and no compositional zoning was observed. Initial results show that the addition of Cu and Ni to the sulfide liquid decreases the O content of that sulfide liquid at a given FeO value of the silicate melt. This will most certainly affect the partitioning of the elements of interest – preliminary results for Pt confirm this by its variation by three orders of magnitude at a given FeO content. Preliminary results also show that Pd, Ru, Pt, Ir are all preferentially partitioned into the metallic liquid instead of the sulfide melt, confirming their preference for S-poor alloys relative to S-rich liquids.
Report Summary: Twelve high-pressure experiments on a piston cylinder press were performed at 1 GPa and 1673-1873 K to systematically investigate the sulfide-silicate partitioning of chalcophile elements as a function of (non-FeO) silicate melt compositional terms. Run times at peak conditions varied around 70 to 220 minutes. The starting compositions consisted of silicate and sulfide powders. The experimental run products consist of well-segregated sulfide blebs in a silicate glass. The glass contains minute sulfur blebs but subsequent LA-ICP-MS measurements showed that these blebs do not contain the elements of interest and are composed of Fe-S-O. Electron microprobe and LA-ICP-MS analyses further showed that the experimental run products are homogeneous and no compositional zoning was observed.
Initial results show that variations in silicate melt composition affect the partitioning of chalcophile elements in a non-ideal way – i.e. FeO activity varies significantly across different melt compositions, thereby affecting the geochemical behavior of the elements of interest. Therefore, it can be expected that in an arc-type differentiation suite the sulfide-silicate partitioning behavior may vary significantly, purely due to variations in FeO activity due to variable silicate melt compositions.
Analyses of Martian meteorites and their components predicts the existence of three main geochemical reservoirs on Mars, namely an enriched crust, a complementary depleted lithospheric mantle, and, lastly, a primitive asthenospheric mantle. Investigating the oxygen isotope composition of these reservoirs is critical for a full understanding of the accretion history of Mars. The Δ17 O composition of ~0.3‰, defined by the SNCs is believed to reflect the primary planetary composition of the martian mantle (1). However, analyses of ancient (>4.5 Ga) individual zircons and minerals from the NWA 7533 regolith breccia, record Δ17 O values that are characterized by a much heavier Δ17 O composition and thus different from the SNCs (2,3). A population of young zircons (<1.5 Ga), also from NWA 7533, are derived from a primitive reservoir located in the deep martian interior, as they are characterized by chondritic-like initial Hf isotope composition (4).
The oxygen isotope composition of a single grain from this population, indicate that this reservoir may be characterised by a different Δ17 O than the SNCs. If correct, the SNCs might not be representative of the bulk martian composition, but plausibly reflecting interaction with a heavy Δ17 O surface reservoir. Therefore, a main objective behind this study was to obtain high-precision oxygen isotope composition of 10 SNC meteorites to potentially detect Δ17 O heterogeneity. However, initial results show no isotopic variability, thus suggesting that the SNC source reservoir has not experienced interaction with surface reservoir, or that any heterogeneity has been erased.
One of the major unresolved questions in the field of cosmochemistry is to understand the source(s) and timing of volatile delivery in the inner Solar System. The goal of this project was to examine primitive achondrites which volatile inventory has not yet been investigated, in order to determine what portion of these volatiles was incorporated in the early stages of the Solar System history, relative to late-veneer delivery. In this regard, primitive achondrite acapulcoites and lodranites were selected as they sample a common parent body, hence allowing to also investigate the effect of various degrees of planetary differentiation on volatile abundances and isotopic compositions.
Using the NanoSIMS 50L at the Open University, we analysed chlorine and water content, as well as their associated isotopic composition in phosphates from three acapulcoites and two lodranites. Our results suggest that the acapulcoite-lodranite parent body incorporated a similar source of volatiles than ordinary chondrites, which chemical composition is similar to the chondritic precursor of acapulcoites and lodranites, arguing for a common reservoir of both Cl and H in the inner Solar System.
20-EPN2-052: Water in silica-bearing iron meteorites – implications for early Solar System dichotomy
Visit by Ana Černok, Freie Universität Berlin (Germany)/University of Trieste (Italy) to TA2 Facility 21 – OU NanoSIMS 50L (UK). Dates of visit: 14-21 November 2022 and virtual visit from 28 November – 20 December 2022
Understanding the volatile inventory of the earliest Solar System is inseparable from understanding which sources contributed to the volatiles of the oldest and relatively dry non-carbonaceous (NC) objects formed in the inner Solar System, and if they were different from wet carbonaceous (CC) materials, formed in the outer Solar System.
Two questions remain largely unanswered in this respect: (i) What are the abundances and isotopic composition of volatiles in the oldest NC objects and (ii) What were their sources? These questions can be answered by investigating some of the oldest objects in the Solar System, namely, the NC iron meteorites.
This Europlanet visit to the NanoSIMS facility was focused on trying to determine the content and isotopic composition of H or H2O inside minerals within iron meteorites. The iron meteorites are some of the oldest formed materials in the Solar System and hold key evidence if there has been any water available when they formed, and if there was: where did this water originate from?
Here we focused on understanding water abundance and its isotopic composition in some of the oldest NC silica bearing iron meteorites (IVA type): Muonionalusta, Gibeon and Steinbach. Other investigated irons did not contain any silica. The lowest water content was measured in Gibeon (< 10 ppm) and Muonionlusta (15–20 ppm), while minerals in Steinbach contained significantly more water (40–120 ppm). The δD values for Gibeon show a large range and greater uncertainties, due to low measured water contents. The δD values in Muonionalusta and Steinbach cluster between ~0–300 ‰. In fact, silica phases in both minerals cluster between ~0–200 ‰, while low-water cpx in Steinbach shows the highest δD values (200–300 ‰). The difference in δD values between mineral phases in Steinbach likely reflects the difference in their crystallisation history, where opx may have lost H resulting in increased D/H ratio (higher δD) due to degassing. Overall, the source of water in these NC irons is very similar to that of the Earth and the chondrites, while low-D reservoirs have not been detected.
Report Summary: A vast range of different gully morphologies occurs on Mars: from the classical gullies, which resemble gullies on Earth, to linear gullies that do not have an Earth counterpart and are found on Martian dunes. Previous experiments have shown that the sublimation of CO2 ice can fluidise and transport sediment in the classical gullies on Mars. However, the linear gullies are hypothesised to form by a different, although related CO2-driven mechanism. For linear dune gullies, it is hypothesised that they form by a block of CO2-ice sliding down the dune. This process has, however, never been observed in real life.
With our visit to the Mars chamber at the Open University, we aimed at deciphering the triggering and forming mechanisms of linear dune gullies on Mars. We identified the possible triggering mechanisms based on hypotheses presented in the literature. The identified mechanisms are; 1) the breaking off and sliding down of CO2-ice blocks, and 2) wind-blown sand being deposited on CO2 frost. We systematically tested these mechanisms in the Mars Chamber at the Open University by means of experiments. For all identified triggering mechanisms a parameter space was used to test the influence of e.g. CO2-ice block size, surface slope and grain size.
With our experiments, we show that CO2-ice blocks slide downslope and create small narrow gullies when dumped on top of fluvial sand, with a large grain-size distribution. However, when dumped on a finer aeolian sand under Martian atmosphere, they do not slide downslope but they dig themselves into the sand, slowly digging a gully downslope by vigorous sublimation and sediment mobilisation. We also show that when a small amount of warm sand is dumped on top of a CO2-frosted the sand is mobilised by CO2 sublimation, but that this process does not create the typical linear gullies we see on Mars.
Report Summary: Our experimental campaign aimed to understand sediment transport driven by CO2 ice sublimation condensed inside a porous regolith. To quantify the erosion of sediment associated with the sublimation of CO2 frost in the subsurface of a ~30° slope, we tested various compositions (MGS-1, sand, sand-dust mixtures). While some sediment showed little to no activity over several attempts (sand), others showed significant slope activity (sand + >=10% MGS clay).
Report Summary: This project was designed to extend previous research of mud behaviour in the low-pressure conditions – with implications for potential sedimentary volcanism on Mars. The main objective was to test the effect of ice (or combined ice-sand) substrate to flow abilities and finite morphology of mudflows. As secondary objectives, testing of various inclinations of the surface, investigation of potential thermal erosion and extended study of another type of surfaces were implemented.
In the first part of the project, nine successful experiments, with pure and variously inclined (2-10°) ice surface, confirmed a different style of mud propagation than in case of the frozen sandy surface. The major observations are: 1) dominant and prevailing boiling of mud mixture during the propagation over deeply frozen ice surface (confirms significance of latent heat related to melting/recrystallization), 2) explosive potential of ice when in contact with the boiling mud (fracturing, contraction-dilatation). The effect of slope in tested range has no significant impact on these observations.
The second type of experiments tested combined ice-sand upper lid. Here, transition between boiling and freezing of mudflows was faster and finite morphology was more similar to lava-like flows which were described by Brož et al. (2020a).
In both cases, the thermal erosion was not confirmed. Moreover, during sectioning and investigation of the finite mudflow shapes and their base, the developed bumps, irregularities or even increased porosity of ice lid were discovered. This might refer to more complex thermal exchange between ice and mud with a sequential melting and re-freezing.
Report Summary: Current hostile conditions on the surface of Mars entail that, if any life form has ever existed on the planet, it may have adopted survival strategies like those evolved by terrestrial microorganisms inhabiting extreme environments e.g. Antarctica. There, one of the most common strategies observed is the cryptoendolithic microbial growth where free-living black fungi living along with algae and lichens within rocky interstices serve as a shield from excessive harmful solar radiation, and their extremotolerance can be mainly due to the presence of thick, highly melanised cell walls.
The ability of these cryptoendolytic microorganisms to thrive under extreme conditions raises the question of whether they cope with them by also regulating their metabolic expression in addition to melanin production, and whether a hypothetical microbial life on Mars could ever have arisen with similar adaptive strategies. In this optic, this study aimed to examin the metabolic regulation of melanised, cryptoendolithic microorganisms in martian scenario. To achieve this goal, colonies of the cryptoendolithic black fungus Cryomyces antarcticus previously exposed to simulated martian conditions such as perchlorates, sulfatic regolith soil and γ radiation, were then analysed with NMR spectrometry at the Center for Microbial Life Detection of the Medical University of Graz. Sample preparation and analysis were carried out in the Facility using standard protocols. Although only preliminary data are available at the time of report writing, significant differences in fungal metabolic expression were observed between the different simulated martian conditions tested.
Report Summary: This project focused on the analysis of three samples from the Black cave (Grotta Nera) located in Majella Park (Abruzzi region, Italy). This cave presents outstanding calcitic moonmilk structures that are unique in the World in terms of both abundance and dimension.
Metagenomic and metabolomic analyses of three samples (A1, apical; A2, lateral; A3, core) collected from one of the moonmilk speleothem from Grotta Nera, were performed. The DNA was extracted using the DNA powersoil kit (Qiagen) modified to include a bead-beating step with MagNA lyser (Roche) for the initial sample treatment. MG-RAST was used to analyse the metagenomic data considering both the taxonomy composition and the functional categories (KO categories). The taxonomy composition of the metagenomic sequences indicated that the dominant phyla were Proteobacteria, Actinobacteria, Firmicutes, Planctomycetes, Acidobacteria, and Verrucomicrobia. Actinobacteria were more abundant in the A1 and A2 as compared to the A3 sample, while in A3 Proteobacteria (in particular, Betaproteobacteria) was enriched as compared to other two samples. The metabolomic analysis was carried out using NMR, extracting the metabolites from 100 mg of each sample (in triplicate). The results indicated that in A2 and A3 samples were enriched by specific metabolites (glycerol in A3 and alanine, acetate, ethanolamine and 3-hydroxybutirate are enriched in A2) suggesting distinct metabolic activities in the microbial communities of these two samples.
Report Summary: This study describes the use of carbonate clumped isotope thermometry as a method of reconstructing paleotemperatures from soil carbonate concretions. The method is based on the tendency of rare, heavy isotopes of carbon and oxygen to clump together in a single CO2 molecule, which is temperature-dependent.
The analysis was performed on 12 samples that forme under a Mediterranean climate regime in Tajikistan to investigate the suitability of these samples for clumped isotope thermometry. The reconstructed temperatures of the Tajik Holocene soil carbonate nodules from three different locations show promising results, indicating that the Δ47 clumped isotope method provides reliable results for this sample type.
The obtained temperature values showed that these carbonates record temperatures that are biased towards summer temperatures. This is likely due to their formation during the summer when temperatures are highest and precipitation ceases after the maximum annual rainfall period. Even the results from older soil carbonates that formed under glacial and interglacial stages dating several glacial cycles back (MIS 11-12 and MIS 21) are well constrained, but a clear difference in formation temperature between glacial and interglacial stages could not be observed. This result can possibly be explained by formation processes of the soil carbonates, but more chronological and temperature data is required to further test this assumption and to investigate which exact period of the geological history is represented by the reconstructed temperatures. Despite these uncertainties, these initial results are very promising and highlight the potential of this method for paleotemperature reconstruction in Central Asia.
Report Summary: Zebra dolomites are marked by an alternation of millimeter thick dark colored, as recrystallised interpreted bands and white cement bands. Disruption of the banding is manifested by displacements that gradually increases and subsequently deceases before disappearing. This disruption also occurs at intracrystalline scale with crystal rehealing features as observable under cathodoluminescence. This disruption of the zebra dolomites is explained by dolomitization in relation to overpressured fluid flow.
In the framework of the Europlanet project zebra dolomite samples from 3 deep Belgian boreholes (Soumagne, Soiron and Bolland) were selected for clumped isotope analysis. The aim was to sample and analyse the dark fine crystalline and white coarse dolomite cements separately to infer the original (re)crystallization temperature. The following research questions were raised: i) is there a systematic difference in deduced temperature between the dark and white dolomite bands. If so then this could help to better constrain the recrystallisation and cementation. This would allow to assess the potential resetting of the original clumped isotope signature of the dark bands due to recrystallisation; ii) if the cement phases display uniform temperatures then this temperature can be compared with the minimum crystallization temperature deduced from primary fluid inclusion microthermometry . The discrepancy between both temperatures, which links to the pressure correction, normally allows to quantify the overpressure of the system; iii) based on deduced crystallization temperature and δ18OPDB, the δ18OSMOW of the fluid can be assessed, allowing to constrain the origin of the dolomitizing fluids, certainly when combined with Sr isotope analysis.
Report Summary: We have measured the clumped carbonate (13C18O16O) isotope ratios, as well as the stable isotope ratios δ18O and δ13C, of a number of bioherm, travertine, and crater fill marl samples from a drill core taken from the Nördlinger Ries Crater (NRC) in Bavaria, Germany. The aim of the project was to make use of the clumped carbonate isotope ratios so as to re-construct a palaeotemperature record of the lake environment, which could be used to assess its habitability in the time since its formation. Such information would be useful for assessing the past habitability of similar crater lake environments on Mars, which are presently of great interest.
At first glance, our results demonstrate that the analysed carbonate samples were formed at temperatures well below what would be expected in the NRC lake environment. On closer inspection, however, it was hypothesised that our carbonate samples were either collected from too high up in the stratigraphy, or they were formed under non-equilibrium conditions and thus suffered from kinetic fractionation effects. The result of the latter is a depression of the precipitation temperature as calculated by palaeothermometric scales.
Future studies are planned to investigate samples from suevite (i.e. the oldest crater infill) and to quantify the extent and causes of these kinetic fractionation effects. Future studies on other crater fill marls may thus also be worthwhile.
Report Summary: High latitude, ice marginal regions are efficient sources for atmospheric dust. Dust plays a fundamental role in the Earth’s climate system both driving and responding to climate change. Last glacial loess deposits in NW Europe potentially record past dust emissions from regions marginal to the former Eurasian Ice Sheet. However, uncertainties over the age of these deposits essentially limit their potential in reconstructing past dust activity. This project aims to build a detailed chronology of last glacial dust deposition in NW Europe through combined luminescence and 14C dating of loess on Jersey (Channel Islands).
During the Europlanet-funded 6-day research visit to the 14C accelerator mass spectrometry laboratory in Debrecen, Hungary radiocarbon dating of fossil gastropods embedded in the loess was conducted. Preliminary results are in good agreement with the existing, yet unpublished luminescence chronology. However, some ages may underestimate the depositional age due contamination from post depositional carbonate leaching. Nevertheless, the 14C ages from gastropod shells serve as valuable cross check of the OSL data and help to build a more robust age model for the loess section based on two independent dating methods.
Report Summary: The lower German limes, the most northern frontier of the Roman Empire on mainland Europe, was the earliest linear frontier of the Roman Empire. Where the Lower German limes ends in the North Sea, the unique Roman cemetery of Valkenburg Marktveld was excavated that plays a key role in understanding the population dynamics in a Roman borderland and coastal landscape. In addition to our current biomolecular research, AMS radiocarbon dates were proposed of 29 adult individuals who were subjected to isotope and aDNA studies with the aim to establish an essential and reliable dating framework that will contribute to the human story and understanding the human history at the Marktveld site.
Prior to the Europlanet TA visit at the Isotoptech Zrt. AMS laboratory, collagen was successfully extracted from 27 individuals. During the visit, our team had the opportunity to learn how the MICADAS system applied to analyse the collagen samples was operated. The calibrated 14C dates range between 343 BCE to 244 CE. Additional δ13C and δ15N will be used to evaluate the collagen quality and possible impact of reservoir effects. Preliminary analysis shows the presence of four groups: 1) pre-Roman; 2) 100 BCE – 60 CE; 3) up to 125 CE, and finally; 4) and younger than 125 BCE. The associated 87Sr/86Sr show slightly higher mean and more variation in the last two groups than the first two (0.7102 ± 0.0010 vs. 0.7096 ± 0.0009). The 14C data will be reposited in IsoArc
Report Summary: Several relatively rapid spikes in radiocarbon levels have recently been found by radiocarbon analysis of tree rings, most notably the 774-775 AD increase. Additional measurements confirmed this C-14 spike to be a global event and the evaluation of radiocarbon data showed that these excursions could be connected to rapid changes in solar activity. Similar changes in radiocarbon levels have been observed in tree-ring samples from USA and Germany around 660 BC and tree rings from USA around 800 BC. The measurement of annual growth rings from other parts of the world could contribute to the research of rapid changes in past radiocarbon levels and their connection to solar activity.
During this Europlanet visit, we used accelerator mass spectrometry to measure radiocarbon content of dendrochronologically dated tree rings from Yamal peninsula in Siberia covering the periods 836-779 BC and 671-651 BC. The measurements of tree rings from these periods show that the 660 BC and 800 BC excursions are present in tree-ring record from a different part of the world as previous measurements (Germany, Poland and Japan for 660 BC; USA and Japan for 800 BC), and it indicates the events causing these spikes have indeed a global character.
The main objective of the project was to study electron impact processes of small organic compounds, using acetone as the first target.
Record and analyse emission spectra of acetone induced by electron impact at several different energies in the range 10 – 100 eV.
Determine emission cross sections corresponding to selected most intensive transitions in range of impact energies (from the thresholds of selected process to 100 eV).
Identify neutral products of electron impact fragmentation of acetone.
Determine reaction kinetics parameters such as threshold energies for selected electron impact excitation reactions of acetone.
During the first half of the visit, we measured electron-impact spectra of acetone at multiple electron energies and generated partial spectral electron energy map which provides the spectral information at various electron energies and thus the efficiency curves (relative emission cross-section curves). During the second half of the visit, the measured data was partially analysed. The emission band in the range of 415 – 445 nm corresponds to the radiation of CH (A2Δ–X2Π) (ν,ν) fragment. Less intensive radiation of CH (B2Σ−–X2Π) (0,0) fragment was identified within 386 – 402 nm. Several emission lines of hydrogen’s Balmer series Hγ – Hη were detected throughout the spectrum as well. Individual rotational transitions from P, Q, R branches of both CH fragments were identified according to LIFBASE 2.1.1 spectroscopy tool, which is software to chart the spectroscopy of diatomic molecules. The rotational temperature of the LIFBASE spectrum was set to ~ 5000 K.
Report Summary: The experiments initially proposed aimed to investigate the formation and chemical evolution of both glycine and alanine under space relevant conditions. Following a systematic approach, the TA was divided into three projects carried out by a multidisciplinary group of scientist (chemists, biologists, astrophysicists and engineers): looking at (i) experimental insights into the microphysics of molecule destruction and sputtering of CO2 exposed to cosmic rays analogues; (ii) the formation of methyl formate and its isomers (glycolaldehyde and acetic acid) through the systematic irradiation of H2 CO:CO, H2 CO:CH4 , and H2 CO:CH3 OH ice mixtures with 1 MeV and 200 keV H+ ; (iii) and 1 MeV H+ irradiation of pure Glycine and Glycine:CH4 interstellar relevant ice mixtures, exploring the survivability and stability of this amino acid in astrophysical relevant environments.
The three projects were designed with incremental molecular complexity to investigate the chemistry of many precursors of simple amino acids. Moreover, the sub-projects were designed to be connected to other awarded TAs either at ICA or AQUILA (PIs: Ivlev, Ioppolo, and Hopkinson) in a synergic manner. For instance, the work of H2 CO completes the systematic study on methyl formate and its isomers, started at this Europlanet facility 2 years ago, trying to improve the understanding of the standing dichotomy on the formation of glycolaldehyde, methyl formate, and acetic acid. All these species are detected in space in star-forming regions and are considered prebiotic molecules.
Report Summary: The chemistry of sulphur in icy extra-terrestrial settings such as the dense interstellar medium and the outer Solar System remains poorly constrained. In particular, the chemical routes towards the formation of SO2 ice (and other volatile sulphur-bearing species) is not completely understood, despite the detection of this species in interstellar icy grain mantles, on the surface of Europa, and on comets. We have therefore explored the possibility of forming SO2 ice as a result of the irradiation of oxygen-bearing ices (including O2, CO, CO2, H2O, and CH3OH) deposited on top of pure elemental sulphur layers, both of which are known to exist in the dense interstellar medium and the outer Solar System where radiation chemistry may be engendered by galactic cosmic rays or the solar wind.
Our results demonstrate that SO2 may indeed be produced after the 1 MeV He+ ion irradiation of O2 and CO2 ices deposited on top of elemental sulphur, but not as a result of similar irradiations conducted using CO, H2O, or CH3OH ices. Other volatile radiation product species incorporating sulphur, such as CS2, OCS, and H2SO4, were also detected in different experiments. Our work should therefore contribute to a better understanding of solid-phase sulphur astrochemistry and the role of elemental sulphur in the formation of volatile sulphur-bearing species in icy extra-terrestrial settings.