Ice Mixtures Research Articles

Ammonium hydrosulfide (NH_4SH) as a potentially significant sulfur sink in interstellar ices

Sulfur is depleted with respect to its cosmic standard abundance in dense star-forming regions. It has been suggested that this depletion is caused by the freeze-out of sulfur on interstellar dust grains, but the observed abundances and upper limits of sulfur-bearing ices remain too low to account for all of the missing sulfur. Toward the same environments, a strong absorption feature at sim 6.85 mu m is observed, but its long-standing assignment to the NH$_ $ cation remains tentative. We aim to spectroscopically investigate the plausibility of NH$_ $SH salt serving as a sulfur reservoir and a carrier of the 6.85 mu m band in interstellar ices by characterizing its IR signatures and apparent band strengths in water-rich laboratory ice mixtures. We then use this laboratory data to constrain NH$_ $SH abundances in observations of interstellar ices. Laboratory transmission IR spectra of NH$_ $:H$_ $S ice mixtures both with and without H$_ $O were collected. The apparent band strengths of the NH$_ $ asymmetric bending ($ $) mode and the SH$^ $ stretching mode in H$_ $O-containing mixtures were calculated with Beer's law plots. The IR features of the laboratory salts were compared to those observed toward a sample of four protostars (two low-mass, two high-mass) and two cold dense clouds without star formation. Apparent band strengths ranging from 3.2(pm 0.3)-3.6(pm 0.4)times 10$^ $ cm molec$^ $ and 3.1(pm 0.4)-3.7(pm 0.5)times 10$^ $ cm molec$^ $ are calculated for the NH$_ $ mode at sim 6.8 mu m/1470 cm$^ $ and the SH$^ $ stretching mode at sim 3.9 mu m/2560 cm$^ $, respectively, in NH$_ $SH:H$_ $O mixtures. The peak position of the NH$_ $ mode redshifts with increasing temperature but also with increasing salt concentration with respect to matrix species H$_ $O and NH$_ $. The observed 6.85 mu m feature is fit well with the laboratory NH$_ $SH:H$_ $O ice spectra. NH$_ $ column densities obtained from the 6.85 mu m band range from 8-23<!PCT!> with respect to H$_ $O toward the sample of protostars and dense clouds. These column densities are consistent with the optical depths observed at 3.9 mu m (the SH$^ $ stretching mode spectral region). A weak and broad feature observed at sim 5.3 mu m/1890 cm$^ $ is tentatively assigned to the combination mode of the NH$_ $ mode and the SH$^ $ libration. The combined upper limits of four other counter-anion candidates, OCN$^ $, CN$^ $, HCOO$^ $, and Cl$^ $, are determined to be lesssim 15-20<!PCT!> of the total NH$_ $ column densities toward three of the protostars. The redshift of the 6.85 mu m feature correlates with higher abundances of NH$_ $ with respect to H$_ $O in both the laboratory data presented here and observational data of dense clouds and protostars. The apparent band strength of the SH$^ $ feature is likely too low for the feature to be detectable in the spectrally busy 3.9 mu m region, but the 5.3 mu m NH$_ $ + SH$^ $ R combination mode may be an alternative means of detection. Its tentative assignment adds to mounting evidence supporting the presence of NH$_ $ salts in ices and is the first tentative observation of the SH$^ $ anion toward interstellar ices. If the majority (gtrsim 80-85<!PCT!>) of the NH$_ $ cations quantified toward the investigated sources in this work are bound to SH$^ $ anions, then NH$_ $SH salts could account for up to 17-18<!PCT!> of their sulfur budgets.

Impact of Harvest Method on Development of European Sea Bass Skin Microbiome during Chilled Storage

European sea bass (Dicentrarchus labrax) is one of the most significant species farmed in the Mediterranean, yet a very perishable product. Its quality deteriorates rapidly as a result of three mechanisms: microbial activity, chemical oxidation, and enzymatic degradation. Microbial spoilage is the mechanism that contributes most to the quality deterioration of fresh and non-processed fish. To this end, our study aims to identify for the first time the combined effect of aquatic environment and harvest method on the composition and trajectory at storage at 0 °C of the European sea bass skin microbiome. Sampling was performed in two commercial fish farms in Western (WG) and Central Greece (CG) where fish were harvested using different methods: direct immersion in ice water or a mixture of slurry ice; application of electro-stunning prior to immersion in ice water. Samples were collected on harvest day and one week post-harvest. To profile the bacterial communities in the fish skin, 16S ribosomal RNA gene sequencing was used. The results and the following analyses indicated that the aquatic environment shaped the original composition of the skin microbiome, with 815 ASVs identified in the WG farm as opposed to 362 ASVs in the CG farm. Moreover, Pseudomonas and Pseudoalteromonas dominated the skin microbiome in the WG farm, unlike the CG farm where Shewanella and Psychrobacter were the dominant genera. All these genera contain species such as Shewanella putrefaciens, Pseudomonas aeruginosa, Pseudoalteromonas spp., and Psychrobacter sp., all of which have been implicated in the deterioration and spoilage of the final product. The different harvest methods drove variations in the microbiome already shaped by the aquatic environment, with electro-stunning favoring more diversity in the skin microbiome. The aquatic environment in combination with the harvest method appeared to determine the skin microbiome trajectory at storage at 0 °C. Although Shewanella had dominated the skin microbiome in all samples one week post-harvest, the diversity and the relative abundance of genera were strongly influenced by the aquatic environment and the harvest method. This study sheds light on the hierarchy of the factors shaping the fish skin microbiome and their importance for controlling post-harvest quality of fresh fish.

Competitive Entrapment of Hypervolatiles in Interstellar and Cometary Water Ice Analogs

The distribution of chemical species in protoplanetary disks around young stars, especially their division between gas and solid phases, fundamentally shapes the composition of future planets and planetesimals. This distribution is likely affected by entrapment, a mechanism whereby volatile species are mechanically or chemically bound within a less volatile ice. In this study, we investigate the entrapment efficiencies of four hypervolatiles (CH4, CO, N2, and Ar) in multicomponent water ice mixtures deposited at different temperatures and mixture ratios. At low ice deposition temperatures, we observe small differences in entrapment efficiency (CH4>CO>N2∼Ar) up to a factor of two across species. The differences in entrapment between species increase by up to an order of magnitude with increasing deposition temperature. The relative entrapment efficiencies are also impacted by changes in the overall hypervolatile concentration of the ice mixtures. Collectively, these experiments suggest that relative entrapment efficiencies are mainly regulated by small differences in binding energies to the ice matrix, though competition for the best sites also influences entrapment in more concentrated ices. We use these results to better inform interpretations of hypervolatile observations in comets and related objects.

Performance analysis of precooling systems for cryogenic carbon capture: A comparative study of theoretical, numerical, and experimental methods

The urgency of addressing climate change has necessitated innovative and practical approaches to reducing greenhouse gas emissions. Cryogenic Carbon Capture (CCC) technology has emerged as a promising solution for capturing CO2 from industrial emissions. This study investigates a simplified design for a precooling system within CCC technology, focusing on optimizing the efficiency and reliability of the system while minimizing energy consumption. The research examines the effects of CO2 concentration in a gas mixture (simulated flue gas, nitrogen and carbon dioxide), cooling bath temperature, and gas mixture flow rate on the performance of heat exchangers in the precooling system. Theoretical, numerical, and experimental analyses were conducted to assess the system's performance. The use of liquid nitrogen at −196 °C in the cooling bath was found unsuitable due to CO2 freezing within the pipes. Instead, a mixture of dry ice and isopropyl alcohol at −78.5 °C proved effective in maintaining consistent temperature and pressure conditions without causing CO2 blockages. Numerical simulations highlighted the importance of optimizing pipe length to balance temperature control and pressure dynamics, with a 140 cm pipe length identified as optimal for heat exchanger design. Experimental results revealed that longer pipes enhance cooling performance due to increased heat exchange surface area, while higher CO2 compositions and flow rates result in higher outlet temperatures and pressures. The study emphasizes the need for further research and simulation work to refine heat exchanger designs for industrial applications, aiming to develop systems that maximize cooling efficiency while ensuring reliable operation.

High strain-rate behavior of polycrystalline and granular ice: An experimental and numerical study

We study the stress–strain response of two different types of ice, viz. polycrystalline ice and granular ice, between −1° – 0 °C over a strain-rate range of 100s−1 to 300s−1 employing the split Hopkinson pressure bar (SHPB). Polycrystalline ice samples, prepared by freezing water in plastic moulds, exhibit a compressive strength ranging from 7 to 10 MPa within the considered strain-rate range. The strain at peak stress remains below 0.2%, indicating brittle behavior. The stress-strain curve of polycrystalline ice displays a prolonged tail, suggesting that the damaged ice specimen retains some strength. High-speed imaging during tests reveals the damage mechanism in ice is fragmentation and axial splitting. A user subroutine based on the Johnson–Holmquist II (JH-2) model is implemented in the commercial finite element (FE) software ABAQUS to predict ice's response at high strain-rates, which captures the softening present in the experimental stress–strain curve. Intact strength parameters and strain-rate sensitivity constants in the JH-2 model are determined from our experimental data and literature results, ensuring alignment with experimental peak stress. Fractured strength and damage evolution parameters are determined by matching post-peak responses from simulations to experiments. Temporal damage evolution from FE simulations aligns well with high-speed images from experiments, providing additional validation. Extending the study to granular ice, samples are prepared by crushing polycrystalline ice and refreezing it. The compressive strength of granular ice at a nominal strain-rate of 200±50s−1 is found to be 4±0.7 MPa. The granular ice, which is a mixture of polycrystalline ice and voids, is homogenized using rule-of-mixture to obtain the elastic properties. The FE simulation results utilizing the JH-2 parameters that we determine matches well with the experimental data, demonstrating that the JH-2 model is well suited to predict the high strain-rate behavior of both types of ice.

The strength of outgassed porous dust aggregates

Context. Outgassing of dust-ice aggregates plays an important role on the surfaces of cometary nuclei as well as for snow-line crossings in protoplanetary disks. Aims. To assess the stability of desiccated dust aggregates, we measured the tensile strength of silica dust samples over a wide range of volume filling factors. Methods. We produced these silica dust samples over a wide range of volume filling factors by gently evaporating dust-ice mixtures with various dust-to-ice mass ratios under vacuum conditions. The tensile strengths of these samples were then measured using the standardized Brazilian disk test. Experiments were performed in a vacuum and at room temperature but were also compared to measurements in air at room temperature and in a vacuum at elevated temperatures. Results. For spherical amorphous silica dust, we find no influence of the environmental conditions (air, vacuum, or heating) on the measured tensile strength. However, for angular crystalline silica dust we see a strong increase in tensile strength in a vacuum compared to air and an even higher increase when the samples are heated in a vacuum. For the spherical silica dust samples, we find a characteristic increase in the tensile strength with decreasing particle size. The tensile strength of samples with identical particle sizes increases strongly with an increasing volume filling factor. Extrapolation of our data to a volume filling factor of 0.1 (90% porosity) shows that a tensile strength as low as 1 Pa can be reached. Conclusions. Numerical simulations show that evaporating water ice in the subsurface layers of comets can reach gas pressures of ~1 Pa. Thus, a desiccated dust layer with a 10% volume filling factor should be detachable and released into the cometary coma. Using a relation between the tensile strength and the critical fragmentation energy, we predict the break-up speed of dust aggregates in mutual collisions as a function of the volume filling factor. Furthermore, we discuss the susceptibility of the aggregates to ram pressure. These values are relevant for protoplanetary disk research and for meteoroids entering planetary atmospheres.

Characterization of carbon dioxide on Ganymede and Europa supported by experiments: Effects of temperature, porosity, and mixing with water

Context. The surfaces of icy moons are primarily composed of water ice that can be mixed with other compounds, such as carbon dioxide. The carbon dioxide (CO2) stretching fundamental band observed on Europa and Ganymede appears to be a combination of several bands that are shifting location from one moon to another. Aims. We investigate the cause of the observed shift in the CO2 stretching absorption band experimentally. We also explore the spectral behaviour of CO2 ice by varying the temperature and concentration. Methods. We analyzed pure CO2 ice and ice mixtures deposited at 10 K under ultra-high vacuum conditions using Fourier-transform infrared (FTIR) spectroscopy and temperature programmed desorption (TPD) experiments. Laboratory ice spectra were compared to JWST observation of Europa’s and Ganymede’s leading hemispheres. The simulated IR spectra were calculated using density functional theory (DFT) methods, exploring the effect of porosity in CO2 ice. Results. Pure CO2 and CO2-water ice show distinct spectral changes and desorption behaviours at different temperatures, revealing intricate CO2 and H2O interactions. The number of discernible peaks increases from two in pure CO2 to three in CO2-water mixtures. Conclusions. The different CO2 bands were assigned to ν̃3,1 (2351 cm−1, 4.25 μm) caused by CO2 dangling bonds (CO2 found in pores or cracks) and ν̃3,2 (2345 cm−1, 4.26 μm) due to CO2 segregated in water ice, whereas ν̃3,3 (2341 cm−1, 4.27 μm) is due to CO2 molecules embedded in water ice. The JWST NIRSpec CO2 spectra for Ganymede and for Europa can be fitted with two Gaussians attributed to ν̃3,1 and ν̃3,3. For Europa, ν̃3,1 is located at lower wavelengths due to a lower temperature. The Ganymede data reveal latitudinal variations in CO2 bands, with ν̃3,3 dominating in the pole and ν̃3,1 prevalent in other regions. This shows that CO2 is embedded in water ice at the poles and it is present in pores or cracks in other regions. Ganymede longitudinal spectra reveal an increase of the CO2 ν̃3,1 band throughout the day, possibly due to ice cracks or pores caused by large temperature fluctuations.

Dynamics of landslides on ice-rich space objects

This work is aimed at investigating the velocity of landslides on ice-containing cosmic bodies of low gravity. We performed a series of experiments dealing with the sliding of desiccated sand on ice and ice-containing mixtures. Measurements were performed in vacuum and at normal pressure in different spatial scales. The values of the velocity derived from the results of experiments were scaled using the gravitational acceleration relevant for the space objects of different sizes: the nuclei of comets and the dwarf planet Ceres. We have found, that the average velocity of material sliding down a hundred meters long slope on the nucleus of a comet should be of the order 0.01 m s−1, while the velocity of dry landslides on Ceres should be two orders of magnitude higher.

Formation and desorption of sulphur chains (H2Sx and Sx) in cometary ice: effects of ice composition and temperature

ABSTRACT The reservoir of sulphur accounting for sulphur depletion in the gas of dense clouds and circumstellar regions is still unclear. One possibility is the formation of sulphur chains, which would be difficult to detect by spectroscopic techniques. This work explores the formation of sulphur chains experimentally, both in pure H$_2$S ice samples and in H$_2$O:H$_2$S ice mixtures. An ultrahigh vacuum chamber, ISAC, eqquipped with FTIR and QMS, was used for the experiments. Our results show that the formation of H$_2$S$_x$ species is efficient, not only in pure H$_2$S ice samples, but also in water-rich ice samples. Large sulphur chains are formed more efficiently at low temperatures ($\approx$10 K), while high temperatures ($\approx$50 K) favour the formation of short sulphur chains. Mass spectra of H$_2$S$_x$, x = 2–6, species are presented for the first time. Their analysis suggests that H$_2$S$_x$ species are favoured in comparison with S$_x$ chains. Nevertheless, the detection of several S$_x^+$ fragments at high temperatures in H$_2$S:H$_2$O ice mixtures suggests the presence of S$_8$ in the irradiated ice samples, which could sublimate from 260 K. ROSINA instrument data from the cometary Rosetta mission detected mass-to-charge ratios 96 and 128. Comparing these detections with our experiments, we propose two alternatives: (1) H$_2$S$_4$ and H$_2$S$_5$ to be responsible of those S$_3^+$ and S$_4^+$ cations, respectively, or (2) S$_8$ species, sublimating and being fragmented in the mass spectrometer. If S$_8$ is the parent molecule, then S$_5^+$ and S$_6^+$ cations could be also detected in future missions by broadening the mass spectrometer range.

Sublimation of volatiles from H2O:CO2 bulk ices in the context of comet 67P/Churyumov–Gerasimenko

Context. The ROSINA instrument on board the Rosetta spacecraft measured, among others, the outgassing of noble gases from comet 67P/Churyumov–Gerasimenko. The interpretation of this dataset and unravelling underlying desorption mechanisms requires detailed laboratory studies. Aims. We aim to improve our understanding of the desorption patterns, trapping, and fractionation of noble gases released from the H2O:CO2-dominated ice of comet 67P. Methods. In the laboratory, ice films of neon, argon, krypton, or xenon (Ne, Ar, Kr, and Xe) mixed in CO2:H2O were prepared at 15 K. Temperature-programmed desorption mass spectrometry is employed to analyse the desorption behaviour of the noble gases. Mass spectrometric ROSINA data of 67P were analysed to determine the fraction of argon associated with CO2 and H2O, respectively. Results. CO2 has a significant effect on noble gas desorption behaviour, resulting in the co-release of noble gases with CO2, decreasing the amount of noble gas trapped within water, shifting the pure phase noble gas peak desorption temperature to lower temperatures, and prolonging the trapping of neon. These effects are linked to competition for binding sites in the water ice and the formation of crystalline CO2. Desorption energies of the pure phase noble gas release were determined and found to be higher than those previously reported in the literature. Enhancement of the Ar/Kr and Ar/Xe ratios are at best 40% and not significantly influenced by the addition of CO2. Analysis of ROSINA mass spectrometric data shows that the fraction of argon associated with H2O is 0.53 ± 0.30, which cannot be explained by our laboratory results. Conclusions. Multicomponent ice mixtures affect the desorption behaviour of volatiles compared to simple binary mixtures and experiments on realistic cometary ice analogues are vital to understanding comet outgassing.

Formation of N–bearing complex organic molecules in molecular clouds: Ketenimine, acetonitrile, acetaldimine, and vinylamine via the UV photolysis of C2H2 ice

Context. The solid-state C2H2 chemistry in interstellar H2O-rich ice has been proposed to explain astronomically observed complex organic molecules (COMs), including ketene (CH2CO), acetaldehyde (CH3CHO), and ethanol (CH3CH2OH), toward early star-forming regions. This formation mechanism is supported by recent laboratory studies and theoretical calculations for the reactions of C2H2+OH/H. However, the analog reaction of C2H2+NH2 forming N-bearing species has been suggested to have a relatively low rate constant that is orders of magnitude lower than the value of C2H2+OH. Aims. This work extends our previous laboratory studies on O-bearing COM formation to investigate the interactions between C2H2 and NH3 ice triggered by cosmic ray-induced secondary UV photons under molecular cloud conditions. Methods. Experiments were performed in an ultra-high vacuum chamber to investigate the UV photolysis of the C2H2:NH3 ice mixture at 10 K. The ongoing chemistry was monitored in situ by Fourier-transform infrared spectroscopy as a function of photon fluence. The IR spectral identification of the newly formed N-bearing products was further secured by a quadrupole mass spectrometer during the temperature-programmed desorption experiment. Results. The studied ice chemistry of C2 H2 with NH2 radicals and H atoms resulting from the UV photodissociation of NH3 leads to the formation of several N-bearing COMs, including vinylamine (CH2CHNH2), acetaldimine (CH3CHNH), acetonitrile (CH3CN), ketenimine (CH2CNH), and tentatively ethylamine (CH3CH2NH2). The experimental results show an immediate and abundant CH2CHNH2 yield as the first-generation product, which is further converted into other chemical derivatives. The effective destruction and formation cross-section values of parent species and COMs were derived, and we discuss the chemical links among these molecules and their astronomical relevance.

A laboratory infrared model of astrophysical pyrimidines

ABSTRACT Nucleobases are essential molecules for life, forming integral parts of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) in all terrestrial life forms. Despite evidence of their abiotic synthesis in meteorites and laboratory simulations of interstellar medium (ISM) conditions, nucleobases have not been detected in the ISM. This study investigates the infrared spectra of uracil, cytosine, and thymine – pyrimidine nucleobases – embedded in an ice mixture simulating common volatiles found in protostellar discs. Our objective was to explore the feasibility of identifying unique infrared bands of pyrimidines in the ISM, despite significant overlapping absorption features from simpler, more abundant interstellar species such as H2O, CO, CH3OH, and NH3. Laboratory results revealed that although two common bands (1240 and 760 cm−1 in uracil; 1236 and 763 cm−1 in cytosine; and 1249 and 760 cm−1 in thymine) were identified, the detection of these bands in space is challenged by overlapping absorption features. Recent observations with the JWST have shown that interstellar organic species exhibit infrared signals within similar ranges, making it impossible to distinguish pyrimidine bands from these organics. Thus, detecting pyrimidines with current telescopes is infeasible, not due to sensitivity limitations or the need for more powerful instrumentation, but because of the intrinsic overlap in spectral features. This study complements previous research on purines by examining pyrimidines and including the impact of common ISM volatiles in the ice composition. The results highlight the significant challenges in detecting complex molecules in the ISM, underscoring the importance of understanding the spectral complexities and interactions to interpret astronomical observations accurately.

JWST detections of amorphous and crystalline HDO ice toward massive protostars

Tracing the origin and evolution of interstellar water is key to understanding many of the physical and chemical processes involved in star and planet formation. Deuterium fractionation offers a window into the physicochemical history of water due to its sensitivity to local conditions. The aim of this work is to utilize the increased sensitivity and resolution of the James Webb Space Telescope (JWST) to quantify the HDO/H$_ $O ratio in ices toward young stellar objects (YSOs) and to determine if the HDO/H$_ $O ratios measured in the gas phase toward massive YSOs (MYSOs) are representative of the ratios in their ice envelopes. Two protostars observed in the Investigating Protostellar Accretion (IPA) program using JWST NIRSpec were analyzed: HOPS 370, an intermediate-mass YSO (IMYSO), and IRAS 20126+4104, a MYSO. The HDO ice toward these sources was quantified via its 4.1 mu m band. The contributions from the CH$_ $OH combination modes to the observed optical depth in this spectral region were constrained via the CH$_ $OH 3.53 mu m band to ensure that the integrated optical depth of the HDO feature was not overestimated. H$_ $O ice was quantified via its 3 mu m band. New laboratory IR spectra of ice mixtures containing HDO, H$_ $O, CH$_ $OH, and CO were collected to aid in the fitting and chemical interpretation of the observed spectra. HDO ice is detected above the 3sigma level in both sources. It requires a minimum of two components, one amorphous and one crystalline, to obtain satisfactory fits. The H$_ $O ice band at 3 mu m similarly requires both amorphous and crystalline components. The observed peak positions of the crystalline HDO component are consistent with those of annealed laboratory ices, which could be evidence of heating and subsequent recooling of the ice envelope (i.e., thermal cycling). The CH$_ $OH 3.53 mu m band is fit best with two cold components, one consisting of pure CH$_ $OH and the other of CH$_ $OH in an H$_ $O-rich mixture. From these fits, ice HDO/H$_ $O abundance ratios of 4.6pm 1.8times 10$^ $ and 2.6pm 1.2times 10$^ $ are obtained for HOPS 370 and IRAS 20126+4104, respectively. The simultaneous detections of both crystalline HDO and crystalline H$_ $O corroborate the assignment of the observed feature at 4.1 mu m to HDO ice. The ice HDO/H$_ $O ratios are similar to the highest reported gas HDO/H$_ $O ratios measured toward MYSOs and the hot inner regions of isolated low-mass protostars, suggesting that at least some of the gas HDO/H$_ $O ratios measured toward massive hot cores are representative of the HDO/H$_ $O ratios in ices. The need for an H$_ $O-rich CH$_ $OH component in the CH$_ $OH ice analysis supports recent experimental and observational results that indicate that some CH$_ $OH ice may form prior to the CO freeze-out stage in H$_ $O-rich ice layers.

Experimental determination of forces arising in process of milling ice from road surfaces

Introduction. To ensure the safety and effective cleaning of highways and sidewalks from snow and ice in winter, it is necessary to use special equipment. But even at the stage of creating such equipment, designers need to know what loads will occur on the working equipment during its operation. Therefore, in order to develop milling working bodies for removing ice from road surfaces, it is necessary to conduct an experimental study in order to determine the loads arising on its working body.Materials and methods. The main purpose of the experimental study is to determine the cutting resistance force that occurs on the cutting element of milling working equipment during its application when cleaning ice and snow on highways and sidewalks. To implement the experiment, a pendulum stand was selected, which allows to study the effect of a separate cutting element of a milling cutter on ice.Results. The results obtained make it possible to predict changes in loads on the milling working body during operation. This makes it possible to develop more advanced designs of road milling equipment and modernize existing ones. The use of these dependencies also enables to determine the necessary structural strength of the milling drum for the normal operation of the equipment and to choose a rational section of the cutting elements.Discussion and conclusions. According to the results of the experimental work carried out, the dependences of the ice cutting resistance depending on the thickness of the cut layer, the type of ice (pure, a mixture of ice, sand and compacted snow with impurities, a mixture of frozen layers, frozen paving slabs and a sample of asphalt concrete) and its temperature were obtained.

Lunar regolith water ice simulation method and characterization

The exploration of lunar water resources has always been a cutting-edge topic in human space exploration. This paper presents a method for gas deposition and ice formation to simulate the mixture of ice and regolith in lunar polar shadowed regions. Following the principles of “physical structure equivalence and environmental parameter approximation,” based on the principle of water molecule deposition and adsorption in a cold trap environment, water ice is converted into water vapor by raising the temperature in a vacuum environment. Then, water molecules deposit and adsorb on the surface of dry, low-temperature mineral particles, forming an ice film under the action of the cold trap capture principle. The morphology and occurrence status of the particle surface ice film has been obtained through microscopic characterization of the samples in a cold environment. Vacuum pressure monitoring equipment is used to verify the pressure changes of water during the sublimation and deposition, and the phase diagram of water is analyzed to understand its state changes within the simulated setup. Samples are retrieved from a high-purity nitrogen glove box, and their water content is verified using thermogravimetric analysis (TGA). The effectiveness of the proposed lunar regolith simulation method is validated through macroscopic and microscopic approaches. This method provides high-fidelity samples for lunar water resource utilization, scientific exploration, and payload development on the Moon.

Exploring High‐Pressure Polymorphism in Carbonic Acid through Direct Synthesis from Carbon Dioxide Clathrate Hydrate

AbstractCarbon dioxide (CO2) is widespread in astrochemically relevant environments, often coexisting with water (H2O) ices and thus triggering a great interest regarding the possible formation of their adducts under various thermodynamic conditions. Amongst them, solid carbonic acid (H2CO3) remains elusive, yet being widely studied. Synthetic routes followed for its production have always been characterised by drastic irradiation on solid ice mixtures or complex procedures on fluid samples (such as laser heating at moderate to high pressures). Here we report about a simpler yet effective synthetic route to obtain two diverse carbonic acid crystal structures from the fast, cold compression of pristine clathrate hydrate samples. The two distinct polymorphs we obtained, differing in the water content, have been deeply characterised via spectroscopic and structural techniques to assess their composition and their astonishing pressure stability, checked up to half a megabar, also highlighting the complex correlations between them so to compile a detailed phase diagram of this system. These results may have a profound impact on the prediction and modelisation of the complex chemistry which characterises many icy bodies of our Solar System.

Exploring High-Pressure Polymorphism in Carbonic Acid through Direct Synthesis from Carbon Dioxide Clathrate Hydrate.

Carbon dioxide (CO2) is widespread in astrochemically relevant environments, often coexisting with water (H2O) ices and thus triggering a great interest regarding the possible formation of their adducts under various thermodynamic conditions. Amongst them, solid carbonic acid (H2CO3) remains elusive, yet being widely studied. Synthetic routes followed for its production have always been characterised by drastic irradiation on solid ice mixtures or complex procedures on fluid samples (such as laser heating at moderate to high pressures). Here we report about a simpler yet effective synthetic route to obtain two diverse carbonic acid crystal structures from the fast, cold compression of pristine clathrate hydrate samples. The two distinct polymorphs we obtained, differing in the water content, have been deeply characterised via spectroscopic and structural techniques to assess their composition and their astonishing pressure stability, checked up to half a megabar, also highlighting the complex correlations between them so to compile a detailed phase diagram of this system. These results may have a profound impact on the prediction and modelisation of the complex chemistry which characterises many icy bodies of our Solar System.

Discriminating viscous-creep features (rock glaciers) in mountain permafrost from debris-covered glaciers – a commented test at the Gruben and Yerba Loca sites, Swiss Alps and Chilean Andes

Abstract. Viscous-flow features in perennially frozen talus/debris called rock glaciers are being systematically inventoried as part of the global climate-related monitoring of mountain permafrost. In order to avoid duplication and confusion, guidelines were developed by the International Permafrost Association to discriminate between the permafrost-related landform “rock glacier” and the glacier-related landform “debris-covered glacier”. In two regions covered by detailed field measurements, the corresponding data- and physics-based concepts are tested and shown to be adequate. Key physical aspects which cause the striking morphological and dynamic differences between the two phenomena/landforms concern the following: tight mechanical coupling of the surface material to the frozen rock–ice mixture in the case of rock glaciers, contrasting with essential non-coupling of debris to the glaciers they cover; talus-type advancing fronts of rock glaciers exposing fresh debris material from inside the moving frozen bodies, as opposed to massive surface ice exposed by increasingly rare advancing fronts of debris-covered glaciers; and increasing creep rates and continued advance of rock glaciers as convex landforms with structured surfaces versus predominant slowing down and disintegration of debris-covered glaciers as often concave landforms with primarily chaotic surface structure. Where debris-covered surface ice is or has recently been in contact with thermally controlled subsurface ice in permafrost, complex conditions and interactions can develop morphologies beyond simple either–or-type landform classification. In such cases, the remains of buried surface ice mostly tend to be smaller than the lower size limit of “glaciers” as the term is applied in glacier inventories and to be far thinner than the permafrost in which they are embedded.

Comprehensive laboratory constraints on thermal desorption of interstellar ice analogues

Gas accretion and sublimation in various astrophysical conditions are crucial aspects of our understanding of the chemical evolution of the interstellar medium. To explain grain growth and destruction in warm media, ice mantle formation and sublimation in cold media, and gas line emission spectroscopy, astrochemical models must mimic the gas--solid abundance ratio. Ice-sublimation mechanisms determine the position of snow lines and the nature of gas emitted by and locked inside planetary bodies in star-forming regions. To interpret observations from the interplanetary and extragalactic interstellar mediums, gas phase abundances must be modelled correctly. We provide a collection of thermal desorption data for interstellar ice analogues, aiming to put constraints on the trapping efficiency of water ice, as well as data that can be used to evaluate astrochemical models. We conduct experiments on compact, amorphous H$_2$O films, involving pure ices as well as binary and ternary mixtures. By manipulating parameters in a controlled way, we generate a set of benchmarks to evaluate both the kinetics and thermodynamics in astrochemical models. We conducted temperature-programmed desorption experiments with increasing order of complexity of ice analogues of various chemical compositions and surface coverages using molecular beams in ultrahigh vacuum conditions (1 times 10$^ $ hPa) and low temperatures (10 K). We provide TPD curves of pure ices made of Ar, CO, CO$_2$, NH$_3$, CH$_3$OH, H$_2$O, and NH$_4^+$HCOO$^-$, their binary ice mixtures with compact amorphous H$_2$O, ternary mixtures of H$_2$O : CH$_3$OH : CO, and a water ice made in situ to investigate its trapping mechanisms. Each experiment includes the experimental parameters, ice desorption kinetics for pure species, and the desorption yield (gas--solid ratio) for ice mixtures. From the desorption yields, we find common trends in the trapping of molecules when their abundance is compared to water: compact amorphous water ices are capable of trapping up to 20<!PCT!> of volatiles (Ar, CO, and CO$_2$), sim 3<!PCT!> of CH$_3$OH, and sim 5<!PCT!> NH$_3$ in relation to the water content within the ice matrix; ammonium formate is not trapped in the water ice films, and compact amorphous water ice formed in situ has similar trapping capabilities to a compact amorphous water ice deposited using molecular beams. Deposited or formed in a very compact structure, amorphous water ice of less than 100 layers cannot trap a large fraction of other gases, including CO and CO$_2$. These desorption yields offer insights into the availability of species that can react and form interstellar complex organic molecules during the warm-up phase of ice mantles. Furthermore, in order to be reliable, gas-grain astrochemical models should be able to reproduce the desorption kinetics and desorption yield presented in our benchmark laboratory experiments.

Experimental study on the radiation-induced destruction of organic compounds on the surface of the Moon

Volatile organic molecules and a complex organic refractory material were detected on the Moon and on lunar samples. The Moon’s surface is exposed to a continuous flux of solar UV photons and fast ions, e.g. galactic cosmic rays (GCRs), solar wind (SW), and solar energetic particles (SEPs), that modify the physical and chemical properties of surface materials, thus challenging the survival of organic compounds. With this in mind, the aim of this work is to estimate the lifetime of organic compounds on the Moon’s surface under processing by energetic particles. We performed laboratory experiments to measure the destruction cross section of selected organic compounds, namely methane (CH4), formamide (NH2CHO), and an organic refractory residue, under simulated Moon conditions. Volatile species were deposited at low temperature (17 - 18 K) and irradiated with energetic ions (200 keV) in an ultra-high vacuum chamber. The organic refractory residue was produced after warming up of a CO:CH4 ice mixture irradiated with 200 keV H+ at 18 K. All the samples were analyzed in situ by infrared transmission spectroscopy. We found that destruction cross sections are strongly affected (up to one order of magnitude) by the dilution of a given organic in an inert matrix. Among the selected samples, organic refractory residues are the most resistant to radiation. We estimated the lifetime of organic compounds on the surface of the Moon by calculating the dose rate due to GCRs and SEPs at the Moon’s orbit and by using the experimental cross section values. Taking into account impact gardening, we also estimated the fraction of surviving organic material as a function of depth. Our results are compatible with the detection of CH4 in the LCROSS eject plume originating from layers deeper than about 0.7 m at the Moon’s South Pole and with the identification of complex organic material in lunar samples collected by Apollo 17 mission.