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Enceladus is a prime target in the search for life in our Solar System, having an active plume that is likely to be connected to a large liquid water sub-surface ocean. Using the sensitive near-infrared spectograph instrument on board the James Webb Space Telescope, we searched for organic compounds and characterized the plume’s composition and structure. The observations directly sample the fluorescence emissions of H2O and reveal an extraordinarily extensive plume (up to 10,000 km or 40 Enceladus radii) at cryogenic temperatures (25 K) embedded in a large bath of emission originating from Enceladus’ torus. Intriguingly, the observed outgassing rate (300 kg s−1) is similar to that derived from close-up observations with Cassini 15 years ago, and the torus density is consistent with previous spatially unresolved measurements with Herschel 13 years ago, which indicates that the vigour of gas eruption from Enceladus has been relatively stable over decadal timescales. This level of activity is sufficient to maintain a derived column density of 4.5 × 1017 m−2 for the embedding equatorial torus, and establishes Enceladus as the prime source of water across the Saturnian system. We performed searches for several non-water gases (CO2, CO, CH4, C2H6, CH3OH), but none were identified in the spectra. On the surface of the trailing hemisphere, we observe strong H2O ice features, including its crystalline form, yet we do not recover CO2, CO or NH3 ice signatures from these observations. As we prepare to send new spacecraft into the outer Solar System, these observations demonstrate the unique ability of the James Webb Space Telescope to provide critical support for the exploration of distant icy bodies and cryovolcanic plumes.The extensive water plume that originates from Enceladus and extends up to 40 Enceladus radii is mapped and characterized by JWST. Data suggest a sustained and uninterrupted plume activity spanning decades and a surface dominated by crystalline H2O ice. No other molecules were detected in gaseous form.

Inter- and circumstellar ices comprise different molecules accreted on cold dust particles. These icy dust grains provide a molecule reservoir where particles can interact and react. As the grain acts as a third body, capable of absorbing energy, icy surfaces in space have a catalytic effect. Chemical reactions are triggered by a number of possible processes; (i) irradiation by light, typically UV photons from the interstellar radiation field and Ly- α radiation emitted by excited hydrogen, but also X-rays, (ii) bombardment by particles, free atoms (most noticeably hydrogen, but also N, C, O and D-atoms), electrons, low energy ions and cosmic rays, and (iii) thermal processing. All these effects cause ices to (photo)desorb, induce fragmentation or ionization in the ice, and eventual recombination will make molecules to react and to form more and more complex species. The effects of this solid state astrochemistry are observed by astronomers; nearly 180 different molecules (not including isotopologues) have been unambiguously identified in the inter- and circumstellar medium, and the abundances of a substantial part of these species cannot be explained by gas phase reaction schemes only and must involve solid state chemistry. Icy dust grains in space experience different chemical stages. In the diffuse medium grains are barely covered by molecules, but upon gravitational collapse and darkening of the cloud, temperatures drop and dust grains start acting as micrometer sized cryopumps. More and more species accrete, until even the most volatile species are frozen. In parallel (non)energetic processing can take place, particularly during planet and star formation when radiation and particle fluxes are intense. The physical and chemical properties of ice clearly provide a snapshotroot to characterize the cosmological chemical evolution. In order to fully interpret the astronomical observations, therefore, dedicated laboratory experiments are needed that simulate dust grain formation and processing as well as ice mantle chemistry under astronomical conditions and in full control of the relevant parameters; ice morphology (i.e., structure), composition, temperature, UV and particle fluxes, etc., yielding parameters that can be used for astrochemical modeling and for comparison with the observations. This is the topic of the present manuscript. Laboratory experiments simulating the conditions in space are conducted for decades all over the world, but particularly in recent years new techniques have made it possible to study reactions involving inter- and circumstellar dust and ice analogues at an unprecedented level of detail. Whereas in the past “top-down scenarios” allowed to conclude on the importance of the solid state for the chemical enrichment of space, presently “bottom-up approaches” make it possible to fully quantify the involved reactions, and to provide information on processes at the molecular level. The recent progress in the field of “solid state laboratory astrophysics” is a consequence of the use of ultra high vacuum systems, of new radiation sources, such as synchrotrons and laser systems that allow extensions to wavelength domains that long have not been accessible, including the THz domain, and the use of highly sensitive gas phase detection techniques, explicitly applied to characterize the solid state such as fluorescence, luminescence, cavity ring-down spectroscopy and sophisticated mass spectrometric techniques. This paper presents an overview of the techniques being used in astrochemical laboratories worldwide, but it is incomplete in the sense that it summarizes the outcome of a 3-day workshop of the authors in November 2012 (at the Observatoire de Meudon in France), with several laboratories represented, but not all. The paper references earlier work, but it is incomplete with regard to latest developments of techniques used in laboratories not represented at the workshop.

Ices, silicates and carbonaceous materials have been detected in several astrophysical environments such as interstellar molecular clouds, comets, and planetary surfaces. These solids are continuously exposed to ion irradiation and UV photolysis. Our knowledge on the properties of solids and molecules and on the modification induced by fast ions (keV-MeV) and UV photons is mainly based on laboratory experiments and on the comparison of experimental results with observations. Here we will give a few examples of the role of laboratory experiments to our understanding of the physical and chemical properties of ices in space.

An essential requisite for the appearance and permanence of life on Earth is the onset of a continuous “cycling” of some key atoms and molecules. Cycling of elements probably also occurs on other objects and is driven by biological or a-biological processing. Here we investigate the cycling of some species in the icy Galilean satellites that are exposed to the intense fluxes of energetic particles coming from the Jupiter magnetosphere. Among the most studied effects of particle bombardment, there is the production of molecules not originally present in the sample. These newly synthesized species are irradiated as well and in some circumstances can re-form the original species, giving rise to a “cycle”. Here we discuss the cycling of some atoms (C, N, O, S) incorporated in molecules observed on the surface of the icy Galilean satellites.The results indicate that cycling of carbon atoms starts with solid elemental carbon. Irradiated in the presence of water ice, carbon dioxide is produced and forms carbonic acid and other organics whose irradiation re-produces carbon dioxide and solid carbon. The effect on nitrogen atoms is limited to a continuous cycle among nitrogen oxides (e.g. NO2 produces NO, and N2O).Oxygen is mostly incorporated in water ice. When irradiated, the large majority of the water molecular fragments recombine to re-form water molecules.The sulfur cycle occurs among SO2 (that cannot be produced by ion irradiation only), sulfuric acid and elemental sulfur.The results are discussed in view of their relevance to the expected space observations of the JWST telescope (NASA, ESA, CSA) and the JUICE (ESA) spacecraft.

For about 20 years laboratory research has been carried out on the effects induced by energetic ions on materials (ices, silicates, carbons) of cometary relevance. Here I present some recent results and outline the relevance such laboratory investigations might have for understanding the origin of cometary materials.

We studied, by infrared absorption spectroscopy, icy samples (16 K) of pure water, a mixture N 2 :H 2 O=100:1, and a sample made of N 2 condensed on water ice and diffused in it after warm up to 30 K. We concentrated our efforts in two spectral regions around 3700 cm –1 where the feature due to the O–H dangling bonds in porous amorphous water falls and around 5000 cm –1 where a broad water band is present. We found that in the N 2 :H 2 =100:1 mixture the profile of the broad water feature at about 5000 cm –1 dramatically changed to a very narrow band at about 5300 cm –1 . When N 2 diffuses in water ice a feature at about 5300 cm –1 appears along with the broad 5000 cm –1 band. We also studied some of the effects of ion irradiation (Ar ++ , 60 keV ions) on these icy samples. We found that after processing the feature due to the O–H dangling bonds it reduced in intensity and eventually disappeared. Here we present the experimental results, discuss their astrophysical relevance and suggest that a band at about 5300 cm –1 (1.88 µm) should be searched for on icy surfaces in the outer Solar System, namely Pluto, Triton, Edgeworth–Kuiper Belt Objects, and Centaurs. PACS No.: 68.43Pg

Trans-Neptunian Objects (TNOs) and Centaurs show remarkable colour variationsin the visual and near-infrared spectral regions. Surface alteration processes such asspace weathering (e.g., bombardment with ions) and impact resurfacingmay play an important role in the colour diversity of such bodies. Ion irradiation ofhydrocarbon ices and their mixtures with water ice transforms neutral (grey) surfacecolours of ices to red and further to grey. Along with the ices, TNOs and Centaursprobably contain complex carbonaceous compounds, in particular, complexhydrocarbons. Unlike ices, such refractory organic materials have originally lowvisual albedos and red colours in the visible and near-infrared ranges. Here wepresent the first results of ion irradiation experiments on asphaltite. Asphaltite isa natural complex hydrocarbon material. The reflectance spectra of asphaltite inthe 0.4–0.8 μm range have been recorded before irradiation and after eachirradiation step. We demonstrate that irradiation of this red dark material with30 keV H+ and 15 keV N+ ions gradually transforms its colour from redto grey as a result of carbonization. A moderate increase in the visual albedo hasbeen observed. These results may imply that the surfaces of primitive red objectsoptically dominated by complex refractory organics may show a similar spaceweathering trend. Our laboratory results were compared with published coloursof TNOs and Centaurs. A broad variety of spectral colours observed for TNOs andCentaurs may be reproduced by various spectra of irradiated organics correspondingto different ion fluences. However, such objects probably also contain ices and silicatecomponents which show different space weathering trends. This fact, together with alack of information about albedos, may explain difficulties to reveal correlations between surface colours within TNO and Centaur populations and their other properties, such as absolute magnitudes and orbital parameters.

Carbonaceous extraterrestrial matter is observed in a wide variety of astrophysical environments. Spectroscopic signatures reveal a large variety of chemical structure illustrating the rich carbon chemistry that occurs in space. In order to produce laboratory analogues of the carbonaceous cosmic dust, a new chemical reactor has been built in the Laboratoire de Photophysique Moléculaire. It is a low pressure flat burner providing flames of premixed hydrocarbon/oxygen gas mixtures, closely following the model system used by the combustion community. In such a device the flame is a one-dimensional chemical reactor offering a broad range of combustion conditions and sampling which allows production of many and various by-products. In the present work, we have studied the effect of ion irradiation (200-400 keV), at the Laboratorio di Astrofisica Sperimentale in Catania, on several samples, ranging from strongly aromatic to strongly aliphatic materials. Infrared and Raman spectra were monitored to follow the evolution of the films under study, and characterize the irradiation process-induced modifications.

We have quantitatively studied, by infrared absorption spectroscopy, the CO/CO^sub 2^ molecular number ratio after ion irradiation of ices and mixtures containing astrophysically relevant species such as CO, CO^sub 2^, H^sub 2^O, CH^sub 4^, CH^sub 3^OH, NH^sub 3^, O^sub 2^, and N^sub 2^ at 12-15 K. The ratios have also been measured after warm up to temperatures between 12 and 200 K. As a general result we find that the CO/CO^sub 2^ ratio decreases with the irradiation dose (amount of energy deposited on the sample). In all of the studied mixtures, as expected, it decreases with increasing temperature because of CO sublimation. However the temperature where CO sublimes strongly depends on the initial mixture, remaining at a temperature over 100 K in some cases. Our results might be relevant to interpret the observed CO/CO^sub 2^ ratio in several astrophysical scenarios such as planetary icy surfaces and ice mantles on grains in the interstellar medium.[PUBLICATION ABSTRACT]