Icy Surfaces Research Articles

Preliminary estimation of the detection possibilities of Ganymede’s water vapor environment with MAJIS

The exosphere of Ganymede is the interface region linking the moon’s icy surface to Jupiter’s magnetospheric environment. Its characterization is of key importance to achieve a full understanding of the ice alteration processes induced by the radiation environment. Several scientific instruments that will operate on board the upcoming Jupiter Icy Moons Explorer (JUICE) mission, selected by ESA in the context of its Cosmic Vision programme, have the potential to study Ganymede’s exosphere. Among them, the Moons And Jupiter Imaging Spectrometer (MAJIS) will have the chance to investigate the composition of the moon’s exospheric components and the emission of water molecules. The exospheric water density profile, as obtained from current models, is a crucial parameter for the estimation of the expected signal to noise ratio related to the actual measurement. In lack of an adequate number of Ganymede’s observations from past missions, there is a general difficulty in constraining current exosphere models which are based, in general, on different scenarios and considerations and often show large discrepancies in the estimated spatial distribution of the neutral environment. In this work, we make a preliminary estimation of the expected IR emission from exospheric water molecules, using different modelled density profiles, and we speculate on the possibility of JUICE/MAJIS to detect it. An exercise on the potential plume detection capabilities of MAJIS is also performed. The first necessary step for performing these calculations is a rough comparison of the existing models of Ganymede’s water vapor exosphere. We discuss the characteristics of the neutral environment as derived from different exospheric models available in literature, the role of the ion-surface interactions in the H2O exosphere generation, and the related implications also in view of future observations. We then use the model outputs to estimate different scenarios for the expected non-Local Thermal Equilibrium (non-LTE) emission from these molecules. The results of this study can be of help during the JUICE observation planning phase.

Chemical Desorption versus Energy Dissipation: Insights from Ab Initio Molecular Dynamics of HCO· Formation

Abstract Molecular clouds are the cold regions of the Milky Way where stars form. They are enriched by rather complex molecules. Many of these molecules are believed to be synthesized on the icy surfaces of the interstellar submicron-sized dust grains that permeate the Galaxy. At 10 K thermal desorption is inefficient and, therefore, why these molecules are found in the cold gas has tantalized astronomers for years. The assumption of the current models, called chemical desorption, is that the molecule formation energy released by the chemical reactions at the grain surface is partially absorbed by the grain and the remaining energy causes the ejection of the newly formed molecules into the gas. Here we report accurate ab initio molecular dynamics simulations aimed at studying the fate of the energy released by the first reaction of the H· addition chain to CO, H· + CO HCO·, occurring on a crystalline ice surface model. We show that about 90% of the HCO· formation energy is injected toward the ice in the first picosecond, leaving HCO· with an energy content (10–15 kJ mol−1) of less than half its binding energy (30 kJ mol−1). As a result, in agreement with laboratory experiments, we conclude that chemical desorption is inefficient for this specific system, namely H· + CO on crystalline ice. We suspect this behavior to be quite general when dealing with hydrogen bonds, which are responsible for both the cohesive energy of the ice mantle and the interaction with adsorbates, as HCO·, even though ad hoc simulations are needed to draw specific conclusions on other systems.

Near-infrared Methanol Bands Probe Energetic Processing of Icy Outer Solar System Objects

Abstract Frozen methanol was detected in the outer solar system on the surfaces of the Centaur 5145 Pholus, the Trans-Neptunian Object (55638) 2002 VE95, and more recently on (486958) Arrokoth. The icy surfaces of these objects are subjected to solar and cosmic ions that modify the physico-chemical properties of their surface. To study the effects of ion bombardment on methanol-rich surfaces, we performed experiments of ion irradiation of H2O:CH3OH mixtures and we monitored the evolution of the methanol near-infrared bands. We observed significant variations of the 2.34/2.27 μm methanol band ratios as a function of the irradiation dose. We then used the Arrokoth and Pholus spectra to test the 2.34/2.27 μm band ratio as a probe of irradiation of methanol-rich surfaces, and we estimated the timescales of processing by solar and cosmic ions. Our results indicate that solar energetic particles are the main drivers of changes in the near-infrared spectra of frozen surfaces in the outer solar system.

Deep search for hydrogen peroxide toward pre- and protostellar objects

Context. In the laboratory, hydrogen peroxide (HOOH) was proven to be an intermediate product in the solid-state reaction scheme that leads to the formation of water on icy dust grains. When HOOH desorbs from the icy grains, it can be detected in the gas phase. In combination with water detections, it may provide additional information on the water reaction network. Hydrogen peroxide has previously been found toward ρ Oph A. However, further searches for this molecule in other sources failed. Hydrogen peroxide plays a fundamental role in the understanding of solid-state water formation and the overall water reservoir in young stellar objects (YSOs). Without further HOOH detections, it is difficult to assess and develop suitable chemical models that properly take into account the formation of water on icy surfaces. Aims. The objective of this work is to identify HOOH in YSOs and thereby constrain the grain surface water formation hypothesis. Methods. Using an astrochemical model based on previous work in combination with a physical model of YSOs, the sources R CrA-IRS 5A, NGC C1333-IRAS 2A, L1551-IRS 5, and L1544 were identified as suitable candidates for an HOOH detection. Long integration times on the APEX 12 m and IRAM 30 m telescopes were applied to search for HOOH signatures in these sources. Results. None of the four sources under investigation showed convincing spectral signatures of HOOH. The upper limit for HOOH abundance based on the noise level at the frequency positions of this molecule for the source R CrA-IRS 5A was close to the predicted value. For NGC 1333-IRAS 2A, L1544, and L1551-IRS 5, the model overestimated the hydrogen peroxide abundances. Conclusions. HOOH remains an elusive molecule. With only one secure cosmic HOOH source detected so far, namely ρ Oph A, the chemical model parameters for this molecule cannot be sufficiently well determined or confirmed in existing models. Possible reasons for the nondetections of HOOH are discussed.

Perceived impact of meteorological conditions on the use of public space in winter settlements

This study aimed to assess the impact of meteorological conditions on the use of public space in Scandinavia and Canada. Between September 21 and December 18, 2017, a cross-sectional online survey ‘EAMQ-Climate: space’ was distributed via web-based platforms. Survey responses were received from 361 residents (258 people from Scandinavia and 103 from Canada). The relative impact of the meteorological determinants on the use of public space was calculated, and a factor analysis was performed. Disparities between Canada and Scandinavia as well as between the climate zones represented were analysed using ANOVA. Overall results showed that the most significant meteorological enablers for the use of outdoor public spaces in winter were solar gain, snowfall and snow-covered surfaces. The main barriers were slush-covered and icy surfaces, rainfall and darkness. Wind and cold were conditions with less influence. The impact of rain and ice, however, differed between climatic zones. It was also established that, when addressing the meteorological impact on avoiding the use of public spaces in winter, it is vital to discriminate between conditions related to a) the ground surface and b) ambient conditions, as well as the particular significance of c) snow and sun, and d) darkness. For the design of public space in winter cities, we conclude that designers need to focus on a wider range of weather conditions than sun, wind and cold, and include snow, rainfall, slushy and icy ground and poor visibility. The study suggests that winter public space has a higher climatic design requirement to be successful than streets and pathways that are mainly used for soft mobility.

Expedition to Mars North Pole and Creation: There Is a Scientific Research Base

A project of the expedition to the north pole of Mars, which is carried out in two stages, has been developed. In the first stage, a space refueller and a mobile solar battery are delivered to the icy surface of the north pole of Mars. The delivery is carried out with the help of electric rocket ER-7, driven by the electric rocket engine “MARS”, and the source of electricity is a solar battery from gallium arsenide. In the second stage, the space train is formed from two interconnected ER-7 rockets and an orbital takeoff-landing capsule TLC-2, in which three astronauts land on the surface and carry out a complex of physical, biological and geological researches on Mars surface. The space refueller has been developed, which melts the water ice on the surface of Mars and with the help of an electrolyser and a liquefier produces fuel and oxidizer for the operation of the chemical rocket engine of the takeoff-landing capsule. To move astronauts from the north pole to the equator, a spacecraft— marsoplane, which consists of the electric rocket ER-7 and the takeoff-landing capsule TLC-1 is developed. The duration of the expedition is 110 days at a cost of 2 billion dollars.

Low-temperature chemistry induced by cosmic rays: positive and negative ion desorption from nitrile-bearing astrophysical ice analogues

ABSTRACT In cold core of dark molecular clouds, where the UV radiation from external sources is strongly attenuated, cosmic rays can induce chemical reactions on the surface of ice-covered grains promoting the ejection of the processed material to the gas phase. We report the positive and negative secondary ion emission from pure CH3CN, C2H3CN, and i-C3H7CN ices due to the bombardment of heavy ions (252Cf fission fragments), simulating the incidence of cosmic rays on to icy surfaces. The secondary ions emitted from each sample were analysed by time-of-flight mass spectrometry, using Plasma Desorption Mass Spectrometry technique. Several ionic species were identified, indicating strong fragmentation on the frozen surface. Proton-transfer processes are suggested to play a role for positive ion desorption, as evidenced by the protonated RCNH+ parent molecules and (RCN)nH+ ionic clusters. The high electron affinity of the cyano radical seems to contribute to the strong emission of CN−, as well as anions attributed to the CHmCN− fragment and (RCN)nCN− cluster series. Sputtering and desorption of ion clusters (positive and negative) induced by heavy ion bombardment are suggested to constitute a route by which new neutral or ionized molecular species may be delivered to the gas phase where thermal desorption is negligible.

Evaluation of skid resistance of pervious concrete slabs under various winter conditions for driver and pedestrian users

Skid resistance of pervious concrete (PC) in comparison with traditional portland cement concrete (PCC) was investigated in the laboratory and in the field. Dry, wet, and iced PC surfaces were tested using the British Pendulum Tester (BPT) with two rubber sliders to represent driver and pedestrian users. Also, iced PC surfaces were treated with de- and anti-icing chemicals and then tested using BPT. Skid resistance values were recorded as the British Pendulum Number (BPN). PC slabs cast from one mix design in three compaction levels revealed that minimal correlation existed between PC porosity and BPN. Laboratory-cast PC slabs showed 23%, 27% and 97% higher BPN values relative to PCC slabs under dry, wet and icy surface conditions, respectively. After one icing event, the one-time application of anti- and de-icing agents on PC slabs improved their friction to the allowable BPN level using both MgCl2 and CaCl2. Field testing of five PC installations with various mix designs and surface conditions showed similar or slightly higher BPN than adjacent PCC slabs. Overall, the laboratory testing in this study showed it is possible to produce PC with significantly higher skid resistance relative to traditional concrete, the field testing revealed the importance of regular maintenance, aggregate type and mixture design on the skid resistance of pervious concrete.

Impact of regenerative braking torque blend-out characteristics on electrified heavy road vehicle braking performance

Electric and hybrid vehicles use a co-operative brake system that consists of regenerative brake and friction brake with different dynamic characteristics to obtain adequate deceleration during braking. Hence, the mechanism of braking blend-out (that is the mechanism of switching off regenerative braking) may affect the vehicle braking performance. This work focusses on the development of various co-operative braking strategies (series and parallel) for electrified heavy road vehicles by considering instantaneous braking blend-out and ramp down braking blend-out characteristics. The developed co-operative braking strategies were evaluated in a Hardware-in-Loop experimental setup equipped with TruckMaker® software. The results showed that instantaneous braking blend-out has more impact on vehicle braking performance in terms of momentary magnitude change in the longitudinal deceleration, pitch angle and suspension deflection for a laden vehicle compared with an unladen vehicle on both dry and icy road surfaces. Ramp down braking blend-out reduced these momentary magnitude changes and thereby improved vehicle’s braking performance in terms of stopping distance and ride comfort. The results of this study indicate that ramp down braking blend-out is expected to improve the vehicle dynamic performance during active braking control due to the smooth transition between friction braking torque and regenerative braking torque.

Evaluating the disturbances acting on a spacecraft on orbit around Europa

Jupiter is a tempting body as a target for a space mission. Since this planet owns a complex system of moons, many discoveries and analyses can be done. Its Galilean moons, Io, Europa, Ganymede, and Callisto, are also of interest, especially Europa with the intriguing hypothesis of the oceans below its icy surface. This work aims to study the perturbations on a spacecraft in an orbit around Europa, the gravitational attraction of the Sun, Jupiter, Io, Ganymede, Callisto, and the gravitational potential of Europa are considered.

Catastrophic disruption of icy bodies with sub-surface oceans

Several icy bodies in the outer Solar system have extensive internal oceans. In several bodies the oceans are believed to be so extensive they decouple the interior core from the icy surface. A major evolutionary driver in the Solar System is high speed impacts – which lead to cratering or even disruption of the target body. Here we consider how the presence of an internal ocean modifies the energy density needed to disrupt an icy body with an internal ocean. We find that in laboratory experiments on decimetre scale bodies, the energy density to cause disruption is 16.25 ± 1.35 J kg−1, compared to 18.0 ± 0.7 J kg−1 for solid ice bodies. This suggests that for the purposes of impacts the bodies behave as if a solid with the same density. Predictions of the lifetimes of such icy bodies against impact disruption thus need not take the interior ocean into account.

Reactivity of HCO with CH3 and NH2 on Water Ice Surfaces. A Comprehensive Accurate Quantum Chemistry Study

Interstellar complex organic molecules (iCOMs) can be loosely defined as chemical compounds with at least six atoms in which at least one is carbon. The observations of iCOMs in star-forming regions have shown that they contain an important fraction of carbon in a molecular form, which can be used to synthesize more complex, even biotic molecules. Hence, iCOMs are major actors in the increasing molecular complexity in space and they might have played a role in the origin of terrestrial life. Understand-ing how iCOMs are formed is relevant for predicting the ultimate organic chemistry reached in the interstellar medium. One possibility is that they are synthesized on the interstellar grain icy surfaces, via recombination of previously formed radicals. The present work focuses on the reactivity of HCO with CH3/NH2 on the grain icy sur-faces, investigated by means of quantum chemical simulations. The goal is to carry outa systematic study using different computational approaches and models for the icy surfaces. Specifically, DFT computations have been bench-marked with CASPT2 and CCSD(T) methods, and the ice mantles have been mimicked with cluster models of 1, 2, 18 and 33 H2O molecules, in which different reaction sites have been considered. Our results indicate that the HCO + CH3/NH2 reactions, if they actually occur, have two major competitive channels: the formation of iCOMs CH3CHO/NH2CHO, or the formation of CO + CH4/NH3. These two channels are either barrierless or presentrelatively low ($\leq$ 10 kJ/mol equal to about 1200 K) energy barriers. Finally, we briefly discuss the astrophysical implications of these findings.

An Instantaneous Center of Rotation-Based Extended Kalman Filter Approach for the On-Line Estimation of Wheelchair Tire Slip

Abstract Wheelchair tire slip is a dangerous scenario that can result from powered wheelchair operation on icy or low-friction surfaces. This research applies instantaneous center of rotation (ICR) estimation to a wheelchair application where ICR values should rarely change. Changes in these estimates are used to understand the occurrence of slip and to predict the motion during that slip. Using inputs of position and orientation obtained through laser odometry, an extended Kalman filter (EKF) algorithm is implemented to estimate the changes in wheelchair ICR location estimates that are indicative of slippage. The algorithm is verified via simulation and experimentation using a robotic wheelchair. It is observed that the convergence of the ICR EKF is heavily dependent on the motion history of the wheelchair. Experiments show that ICR locations do not vary significantly under the slip-free conditions of normal operation with 2-σ standard deviations of 0.076 m, but the ICR locations deviate up to 0.84 m during slippage.

A Prospective Injury Surveillance Study on Ski Touring.

Background:Ski touring is an outdoor sport with growing popularity in alpine countries. Information about injuries in ski touring is limited.Purpose:To determine injury rates, mechanisms, causes, and risk factors in ski touring.Study Design:Descriptive epidemiology study.Methods:Between November 2015 and May 2016, a total of 191 participants from the Alps region were prospectively tracked via personalized online questionnaires. Injury rates were calculated per 1000 hours of sports exposure. Risk factors were assessed per multivariate logistic regression analysis.Results:A total of 3900 ski tours were performed, with 10,955 hours and 4,108,503 m in height ascension (uphill) recorded. The overall injury rate was 2.5 injuries per 1000 hours of ski touring. A total of 27 injury-events were reported, of which 18 (67%) were classified as mild, 7 (26%) as moderate, and 2 (7%) as severe. Hands (28%) and knees (16%) were the most commonly involved anatomic regions. Most injuries were limited to the soft tissue, such as bruises (31%) and abrasions (18%). Significantly more injuries happened during the descent (n = 17; 63%) than during the ascent (n = 6; 22%) (odds ratio, 5.96; P = .004), while poor weather conditions, icy surface, and inattentiveness were the most often reported reasons for injury. Sidecountry ski touring was identified as the only significant independent risk factor for injury (P < .001).Conclusion:In this prospective injury surveillance study, the majority of ski touring injuries were mild and limited to the soft tissue. Ski touring injuries were more likely to happen during the descent of a tour, and sidecountry ski touring was the only significant independent risk factor for injury. Bad weather, icy surface, and inattentiveness were found to be the leading causes for an injury-event in this study.

Evaluating Li/CFx Cell Components for Deep Space Space Exploration

To meet the future demands of space exploration will require primary batteries offering higher specific energy, relative to heritage space rated cells based on Li/SO2, Li/SOCl2 and Li/MnO2 chemistries. Cells based on the Li/CFx chemistry are currently under development to support operations in challenging extreme environments. One such proposed application of advanced primary cells is for a proposed Europa Lander, which would analyze the icy surface of this Jovian moon, evaluate its potential for habitability, and investigate for signs of bio-signatures. To address this unique mission requires a detailed understanding of the effects of wide temperatures and radiation on cell electrical and thermal performance, self-discharge characteristics and reliability. In particular, results from screening of cell components will be reviewed, including electrodes and electrolytes experiencing high doses of ionizing radiation. The work described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA) and supported by the Europa Lander Pre-Project.

Production of Hydronium Ion (H3O)+ and Protonated Water Clusters (H2O)nH+ after Energetic Ion Bombardment of Water Ice in Astrophysical Environments.

Water ice exists on many objects in space. The most abundant icy species, among them water, are present in the icy satellites of the outer Solar System giant planets. The nuclei of comets, which are mainly composed of water ice, give another example of its abundance. In the interstellar medium (ISM), ice mantles, formed by molecular species sticking on dust grains, consist mainly of water ice. All these objects are exposed to ionizing radiation like ions, UV photons, and electrons. Sputtering of atoms, molecules, ions, and radicals from icy surfaces may populate and maintain exospheres of icy objects in the Solar System. In other respects, ionized hydrides such as OH+, H2O+, and H3O+ have been detected in the gas phase in star-forming regions. Interactions with cosmic rays could be an additional explanation to the current models for the formation of those species. In fact, laboratory simulations showed that the main components of the sputtered ionic species from water ice are oxygen hydrides. In this work, water ice targets were irradiated at several temperatures (10-200 K) by 90 keV O6+ ions, yielding an electronic stopping power of about 12 eV/Å, when the nuclear stopping power is comparable to the electronic stopping power. Sputtering of secondary ions after bombardment of the ice target was analyzed by time-of-flight mass spectrometry (TOF-SIMS). Besides hydrogen ions (H+, H2+, H3+), also O+, O2+, OH+, (H2O)+, and clusters of (H2O)nH+ with n = 1-8 are emitted. Our results show a progressive yield decrease with increasing temperature of all of the detected species. This is related to the structure of the ice: the ionic sputtering yield for crystalline ice is much lower than for an amorphous ice. For instance, amorphous ice at 10 K exhibits a yield of the order of 2 × 10-6 secondary (H2O)nH+ hydride ions/projectile (with n = 1-8). As the temperature is increasing toward the phase transition to crystalline ice, the yields decrease by about one order of magnitude.

Constructing a Multifrequency Passive Microwave Hail Retrieval and Climatology in the GPM Domain

AbstractLarge hail is a primary contributor to damages and loss around the world, in both agriculture and infrastructure. The sensitivity of passive microwave radiometer measurements to scattering by hail led to the development of proxies for severe hail, most of which use brightness temperature thresholds from 37-GHz and higher-frequency microwave channels on board weather satellites in low-Earth orbit. Using 16+ years of data from the Tropical Rainfall Measuring Mission (TRMM; 36°S–36°N), we pair TRMM brightness temperature–derived precipitation features with surface hail reports in the United States to train a hail retrieval on passive microwave data from the 10-, 19-, 37-, and 85-GHz channels based on probability curves fit to the microwave data. We then apply this hail retrieval to features in the Global Precipitation Measurement (GPM) domain (from 69°S to 69°N) to develop a nearly global passive microwave–based climatology of hail. The extended domain of the GPM satellite into higher latitudes requires filtering out features that we believe are over icy and snowy surface regimes. We also normalize brightness temperature depression by tropopause height in an effort to account for differences in storm depth between the tropics and higher latitudes. Our results show the highest hail frequencies in the region of northern Argentina through Paraguay, Uruguay, and southern Brazil; the central United States; and a swath of Africa just south of the Sahel. Smaller hot spots include Pakistan, eastern India, and Bangladesh. A notable difference between these results and many prior satellite-based studies is that central Africa, while still active in our climatology, does not rival the aforementioned regions in retrieved hailstorm frequency.

Three‐Dimensional Modeling of Callisto's Surface Sputtered Exosphere Environment

AbstractWe study the release of various elements from Callisto's surface into its exosphere by plasma sputtering. The cold Jovian plasma is simulated with a 3‐D plasma‐planetary interaction hybrid model, which produces 2‐D surface precipitation maps for magnetospheric H+, O+, O++, and S++. For the hot Jovian plasma, we assume isotropic precipitation onto the complete spherical surface. Two scenarios are investigated: one where no ionospheric shielding takes place and accordingly full plasma penetration is implemented (no‐ionosphere scenario) and one where an ionosphere lets virtually none of the cold plasma but all of the hot plasma reach Callisto's surface (ionosphere scenario). In the 3‐D exosphere model, neutral particles are sputtered from the surface and followed on their individual trajectories. The 3‐D density profiles show that whereas in the no‐ionosphere scenario the ram direction is favored, the ionosphere scenario produces almost uniform density profiles. In addition, the density profiles in the ionosphere scenario are reduced by a factor of ∼2.5 with respect to the no‐ionosphere scenario. We find that the Neutral Gas and Ion Mass Spectrometer, which is part of the Particle Environment Package on board the JUpiter ICy moons Explorer mission, will be able to detect the different sputter populations from Callisto's icy surface and the major sputter populations from Callisto's nonicy surface. The chemical composition of Callisto's exosphere can be directly linked to the chemical composition of its surface and will offer us information not only on Callisto's formation scenario but also on the building blocks of the Jupiter system.

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Hydrogen isotopic anomalies in extraterrestrial organic matter: role of cosmic ray irradiation and implications for UCAMMs

Context. Micrometeorites represent, at timescales shorter than a few million years, the dominant source of extraterrestrial matter at the surface of the Earth. Analyses of ultracarbonaceous micrometeorites recovered from Antarctica, known as UCAMMs reveal an exceptionally N-rich organic matter associated with spatially extended high D enrichments. Experiments show that this specific organic matter might have been formed in the outer solar system by energetic irradiation of N-rich icy surfaces. Aims. We experimentally investigate the hydrogen isotopic fractionation resulting from irradiation of normal and D-rich N2-CH4 ices by high energy ions, simulating the exposition to Galactic cosmic rays of icy bodies surfaces orbiting at large heliocentric distances. Methods. Films of N2-CH4 ices and a N2-CH4/CD4/N2-CH4 “sandwich” ice were exposed to 129Xe13+ ion beams at 92 and 88 MeV. The chemical evolution of the samples was monitored using in situ Fourier transform infrared spectroscopy. After irradiation, targets were annealed to room temperature. The solid residues of the whole process left after ice sublimation were characterized in situ by infrared spectroscopy, and the hydrogen isotopic composition measured ex situ by imaging secondary ion mass spectrometry at the sub-micron scale (NanoSIMS). Results. Irradiation leads to the formation of new molecules and radicals. After annealing, the resulting poly-HCN-like macro-molecular residue exhibits an infrared spectrum close to that of UCAMMs. The residue resulting from irradiation of N2-CH4 ices does not exhibit a significant deuterium enrichment comparable to that found in extraterrestrial organic matter. The residue formed by irradiation of D-rich ices shows the formation of isotopic heterogeneities with localised hotspots and an extended contribution likely due to the diffusion of the radiolytic products from the D-rich layer. Conclusions. These results show that high-energy cosmic ray irradiation does not induce the large hydrogen isotopic fractionation observed at small spatial scale in interplanetary organics. By contrast, large D/H ratio heterogeneities at the sub-micron spatial scale in extraterrestrial organic matter can result from isotopically heterogeneous ices mixtures (i.e. condensed with different D/H ratios), which were transformed into refractory organic matter upon irradiation.