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1.
The chemistry and spectroscopy of proton-irradiated H2O + O2 ices have been investigated in relation to the production of oxidants in icy satellite surfaces. Hydrogen peroxide (H2O2), ozone (O3), and the hydroperoxy (HO2) and hydrogen trioxide (HO3) radicals have all been observed, and their temperature and dose dependent production trends have been measured. We find that O2 aggregates form during the growth of H2O + O2 ice films, and the presence of these aggregates greatly affects the HO2 and H2O2 yields. In addition, we have found that the position of the spectral maximum of the ν3 vibration of O3 shifts with ice composition, giving an indication of the degree of dispersion of O3 molecules within the ice. We discuss the relevance of these measurements to icy satellite surfaces.  相似文献   

2.
G Strazzulla  G Leto  M.A Satorre 《Icarus》2003,164(1):163-169
Solid surfaces of atmosphereless objects in the Solar System are continuously irradiated by energetic ions (from solar wind and flares, planetary magnetospheres, and cosmic rays). Reactive ions (e.g., H, C, N, O, S) induce all of the effects of any other ion including the synthesis of molecular species originally not present in the target. In addition, these ions have a chance, by implantation in the target, of forming new species containing the projectile. An ongoing research program performed at our laboratory aims at investigating the implantation of reactive ions in many relevant ices (and mixtures) by using IR spectroscopy. Here we present new results obtained by implanting carbon and nitrogen ions in water ice at 16 and 77 K. Carbon implantation produces carbon dioxide and the production yield has been measured. Nitrogen implantation does not produce any N-bearing species detectable by IR spectroscopy. Both ions are also capable of synthesizing hydrogen peroxide at the two investigated temperatures. We show that, although a relevant quantity of CO2 can be formed by C implantation in the icy jovian moons, this is not the dominant formation mechanism of carbon dioxide.  相似文献   

3.
Xiaoning Pan 《Icarus》2004,172(2):521-525
Hydrogen peroxide (H2O2) is one of the minor constituents of the water ice covered surfaces of the jovian satellites Europa, Ganymede, and Callisto. Here we demonstrate that H2O2 production may be initiated by the dissociative electron attachment (DEA) of low-energy electrons (LEEs) to water molecules. Electronic excitation or ionization by electrons also contributes to H2O2 formation at higher electron energies. Finally, we show that hydroperoxyl (HO2) radicals could be formed on the surfaces of icy satellites by LEE impact.  相似文献   

4.
We report a study on the broadband ultraviolet photolysis of methane-water ice mixtures, at low methane concentrations and temperatures relevant to the icy satellites of the outer Solar System. The photochemistry of these mixtures is dominated by the action of hydroxyl radicals on methane and the resulting products. This implies that, given sufficient exposure time, the methane will eventually be completely oxidized to carbon dioxide. The presence of methane inhibits the formation of hydrogen peroxide by serving as a trap for hydroxyl radicals. The distribution of photochemical products is broadly similar to that previously conducted using ion and electron sources, with some differences possibly attributable to the difference in radiation source. The results are applicable to a variety of icy bodies in the Solar System. On Enceladus, where methane mixed with water is measured in the plumes, methane in the surface ices is subject to oxidation and will eventually be converted to CO2. The CH stretch feature detected in the VIMS spectra of the Enceladus surface ice suggests that methane is currently being supplied to the surface ice, likely from re-condensation of the plume gas.  相似文献   

5.
We present infrared absorption studies on the effects of 50-100 keV Ar+ and 100 keV H+ ion irradiation of water ice films at 20-120 K. The results support the view that energetic ions can produce hydrogen peroxide on the surface of icy satellites and rings in the outer Solar System, and on ice mantles on interstellar grains. The ion energies are characteristic of magnetospheric ions at Jupiter, and therefore the results support the idea that radiolysis by ion impact is the source of the H2O2 detected on Europa by the Galileo infrared spectrometer. We found that Ar+ ions, used to mimic S+ impacts, are roughly as efficient as H+ ions in producing H2O2, and that 100 keV H+ ions can produce hydrogen peroxide at 120 K. The synthesized hydrogen peroxide remained stable while warming the ice film after irradiation; the column density of the formed H2O2 is constant until the ice film begins to desorb, but the concentration of H2O2 increases with time during desorption because the water sublimes at a faster rate. Comparing the shape of the 3.5-μm absorption feature of H2O2 to the one measured on Europa shows excellent agreement in both shape and position, further indicating that the H2O2 detected on Europa is likely caused by radiolysis of water ice.  相似文献   

6.
In this review we provide the data needed to interpret remote spectroscopic studies of O2 molecules embedded in the icy surfaces of outer solar system bodies. O2 produced by radiolysis has been seen in the gas phase and as the so-called ‘solid O2’ trapped in the icy surfaces of Ganymede, Europa and Callisto. It may also have been indirectly observed on a number of objects by its radiolysis product, O3. These observations indicate the importance of O2 for understanding the chemical processes occurring on icy outer solar system surfaces. Therefore, the published absorption spectra of gaseous, liquid and solid O2 and of O2 embedded in H2O ice are reviewed in some detail. Particular emphasis has been placed on the presentation of transition probabilities for the various O2 spectral series so that their relative importances can be assessed when they are used for modelling the radiation chemistry occurring in such environments.  相似文献   

7.
We report photochemical studies of thin cryogenic ice films composed of N2, CH4 and CO in ratios analogous to those on the surfaces of Neptune’s largest satellite, Triton, and on Pluto. Experiments were performed using a hydrogen discharge lamp, which provides an intense source of ultraviolet light to simulate the sunlight-induced photochemistry on these icy bodies. Characterization via infrared spectroscopy showed that C2H6 and C2H2, and HCO are formed by the dissociation of CH4 into H, CH2 and CH3 and the subsequent reaction of these radicals within the ice. Other radical species, such as C2, , CN, and CNN, are observed in the visible and ultraviolet regions of the spectrum. These species imply a rich chemistry based on formation of radicals from methane and their subsequent reaction with the N2 matrix. We discuss the implications of the formation of these radicals for the chemical evolution of Triton and Pluto. Ultimately, this work suggests that , CN, HCO, and CNN may be found in significant quantities on the surfaces of Triton and Pluto and that new observations of these objects in the appropriate wavelength regions are warranted.  相似文献   

8.
William K. Hartmann 《Icarus》1980,44(2):441-453
Observational and theoretical data converge on the conclusion that planetesimals in Jupiter's region of the solar nebula were initially composed predominantly of a mixture of roughly 39–70% H2O ice by volume, and 30–61% dark stony material resembling carbonaceous chondrites. Recent observations emphasize a division of most asteroid and satellite surfaces in this region into two distinct groups: bright icy material and dark stony material. The present model accounts for these by two main processes: an impact-induced buildup of a dark stony regolith in the absence of surface thermal disturbance, and thermal-disturbance-induced eruption of “water magmas” that create icy surfaces. “Thermal disturbances” include tidal and radiative effects caused by nearness of a planet. A correlation of crater density and albedo, Ganymede's dark-ray craters, and other observed phenomena (listed in the summary) appear consistent with the model discussed here.  相似文献   

9.
M.H. Moore  R.F. Ferrante  J.N. Stone 《Icarus》2007,190(1):260-273
Although water- and ammonia-ices have been observed or postulated as important components of the icy surfaces of planetary satellites in the outer Solar System, significant gaps exist in our knowledge of the spectra and behavior of such mixtures under astrophysical conditions. To that end, we have completed low-temperature spectroscopic studies (1-20 μm) of water-ammonia mixtures, with an emphasis on features in the near-IR, a region which is accessible to ground-based observations. The influences of composition, formation temperature, thermal- and radiation-processing, and phase (crystalline or amorphous) of the components were examined. Spectra of both pure NH3 and H2O-NH3 icy mixtures with ratios from 0.7 to 57 were measured at temperatures from 10 to 120 K. Conditions for the formation and thermal stability of the ammonia hemihydrate (2NH3⋅H2O) and the ammonia monohydrate (NH3⋅H2O) have been examined. Band positions of NH3 in different H2O-ices and major band positions of the hydrates were measured. We report spectral shifts that depend on concentration and temperature. The radiation-induced amorphization of the hemihydrate was observed and the radiation destruction of NH3 in H2O-ices was measured. Implications of these results for the formation, stability, and detection of ammonia on outer satellite surfaces are discussed.  相似文献   

10.
M.D. Dyar  C.A. Hibbitts 《Icarus》2010,208(1):425-1934
Storage of hydrogen atoms in or on a planetary surface can take place via several different mechanisms. If the hydrogen atom reacts to form a hydroxyl (OH) group or water molecule, an absorption band near 3 μm will be present. Many possible mechanisms for sequestering atomic hydrogen are discussed: internal hydrogen in the form of non-structural OH and H2O in nominally-anhydrous minerals, structural OH in minerals, structural H2O in minerals, H2O in fluid inclusions, and OH and H2O in glasses; bulk H2O as either liquid water or ice; and surficial hydrogen that is either physisorbed as H2O, chemisorbed as an H2O surface complex, or chemically-bound as an OH group on surface terminal sites and grain boundary regions. Understanding the spectroscopic distinctions among these various phenomena is of critical importance in constraining both the evolution of planetary interiors and the cycling of water on planetary surfaces. Proper interpretation of 3-μm bands in reflectance spectra is shown to depend upon the relative contributions from surficial vs. interior hydrogen, which vary with effective surface area (i.e., the grain size and surface roughness) and the volume sampled by the spectrometer.  相似文献   

11.
Molecular composition of comets, planets and satellites surfaces is known to change radically after suffering impacts. New possibilities concerning the presence of volatile molecules in icy surfaces involving retaining processes are studied in this paper. To fulfill this aim we have carried out desorption experiments under high vacuum conditions based on a quadrupole mass spectrometer and a quartz crystal microbalance. From our results, the presence of certain volatiles in some frozen scenarios could be explained by several retaining mechanisms related to the structure of CO2 even when, after impact, temperatures above their characteristic sublimation ones are reached.  相似文献   

12.
E.M. Sieveka  R.E. Johnson 《Icarus》1982,51(3):528-548
The molecular transport of condensed gas species across the surfaces of the icy satellites of Jupiter and Saturn is examined with the view of describing, in part, certain gross visual features associated with these bodies. Molecular redistribution induced by thermal sublimation and magnetospheric plasma-ion impact on satellites with negligible atmospheres is calculated by assuming that the molecules follow ballistic trajectories and by statistically selecting initial molecular velocities and points of origin. Erosion/deposition profiles so calculated are compared for a variety of satellite sizes and environments in order to understand the relative importance of sublimation and cold corotating plasma-ion- and fast plasma-ion-induced transport. The results are scaled to make them useful as new data is available for the icy satellites and their plasma environment. The erosion/deposition profiles are then used to discuss the appearance of a polar frost on Ganymede. A balance of magnetospheric-ion implantation and ion-induced molecular redistribution is used to discuss the observation of embedded SO2 and the darkening of the trailing side on Europa. Ion-induced molecular transport may also limit the deposition of SO2 frost in the polar regions of Io and may be a source of heavy particles in the Jovian and Saturnian magnetospheres.  相似文献   

13.
We present new experimental results on impact shock chemistry into icy satellites of the outer planets. Icy mixtures of pure water ice with CO2, Na2CO3, CH3OH, and CH3OH/(NH4)2SO4 at 77 K were ablated with a powerful pulsed laser—a new technique used to simulate shock processes which can occur during impacts. New products were identified by GC-MS and FTIR analyses after laser ablation. Our results show that hydrogen peroxide is formed in irradiated H2O/CO2 ices with a final concentration of 0.23%. CO and CH3OH were also detected as main products. The laser ablation of frozen H2O/Na2CO3 generates only CO and CO2 as destruction products from the salt. Pulsed irradiation of water ice containing methanol leads also to the formation of CO and CO2, generates methane and more complex molecules containing carbonyl groups like acetaldehyde, acetone, methyl formate, and a diether, dimethyl formal. The last three compounds are also produced when adding ammonium sulfate to H2O/CH3OH ice, but acetone is more abundant. The formation of two hydrocarbons, CH4 and C2H6 is observed as well as the production of three nitrogen compounds, nitrous oxide, hydrogen cyanide, and acetonitrile.  相似文献   

14.
A.D. Kuzmin  B.Y.A Losovsky 《Icarus》1973,18(2):222-223
A model of an icy surface and interior for Callisto gives a predicted thermal radio emission in good agreement with experimental radio astronomical data. The radio brightness temperature of an icy surface will not depend on wavelength. This may be a method to test icy surface hypotheses. The brightness temperatures of other satellites with icy surfaces will be equal to 200–220°K and will not depend on wavelength.  相似文献   

15.
16.
《Planetary and Space Science》1999,47(10-11):1371-1376
Implantation of reactive ions into targets of planetary interest is a relevant subject to be studied in the laboratory. It could in fact produce new molecular species that are not native to those surfaces. Presented here are new laboratory results obtained by nitrogen implantation (15–30 keV N+) on frozen mixtures of H2O:CH4 (2:1). These species have been chosen in view of their possible presence on the surface of Jovian and Saturnian satellites and rings. In fact these surfaces are exposed to intense irradiation by magnetospheric and/or solar energetic particles. The laboratory investigation utilizes IR spectroscopy. The main objectives of the present study are to identify newly produced species and to verify if these (or at least if the profile of their IR bands) are different from those produced by unreactive ions impinging on targets in which nitrogen is already present, occurring in the form of frozen NH3 (Strazzulla and Palumbo, 1998) or N2 (Palumbo et al., 1999). I find that CN-bearing group is in fact formed and its IR feature has a profile (peak position and band profile) that differs from that obtained after irradiation or frozen gases containing nitrogen. The relevance the results might have to elucidate the origin of some species observed on Jovian icy moons or predicted to be observed on Saturnian satellites are outlined.  相似文献   

17.
Previous studies of the photochemistry of small molecules in Titan’s atmosphere found it difficult to have hydrogen atoms removed at a rate sufficient to explain the observed abundance of unsaturated hydrocarbons. One qualitative explanation of the discrepancy nominated catalytic aerosol surface chemistry as an efficient sink of hydrogen atoms, although no quantitative study of this mechanism was attempted. In this paper, we quantify how haze aerosols and macromolecules may efficiently catalyze the formation of hydrogen atoms into H2. We describe the prompt reaction model for the formation of H2 on aerosol surfaces and compare this with the catalytic formation of H2 using negatively charged hydrogenated aromatic macromolecules. We conclude that the PRM is an efficient mechanism for the removal of hydrogen atoms from the atmosphere to form H2 with a peak formation rate of ∼ 70 cm−3 s−1 at 420 km. We also conclude that catalytic H2 formation via hydrogenated anionic macromolecules is viable but much less productive (a maximum of ∼ 0.1 cm−3 s−1 at 210 km) than microphysical aerosols.  相似文献   

18.
The paper discusses the formation and dynamics of the rarefied gas envelope near the icy surface of Jupiter’s moon Ganymede. Being the most massive icy moon, Ganymede can form a rarefied exosphere with a relatively dense near-surface layer. The main parent component of the gas shell is water vapor, which enters the atmosphere due to thermal degassing, nonthermal radiolysis, and other active processes and phenomena on the moon’s icy surface. A numerical kinetic simulation is performed to investigate, at the molecular level, the formation, chemical evolution, and dynamics of the mainly H2O- and O2-dominant rarefied gas envelopes. The ionization processes in these rarefied gas envelopes are due to exposure to ultraviolet radiation from the Sun and the magnetospheric plasma. The chemical diversity of the icy moon’s gas envelope is attributed to the primary action of ultraviolet solar photons and plasma electrons on the rarefied gas in the H2O- or O2-dominant atmosphere. The model is used to calculate the formation and development of the chemical diversity in the relatively dense near-surface envelope of Ganymede, where an important contribution comes from collisions between parent molecules and the products of their photolysis and radiolysis.  相似文献   

19.
E.M. Parmentier  J.W. Head 《Icarus》1981,47(1):100-111
Spacecraft images show that the icy Galilean satellites have surfaces with very low topographic relief. Impact craters on Ganymede and Callisto are anomalously shallow and are characterized by sharp well-defined rims and domed floors. These morphological characteristics can be explained by viscous relaxation of topography on an icy crust in which the viscosity is uniform or decreases with depth. Under these conditions, large craters relax more rapidly than small craters, therefore explaining a possible underabundance of large craters. Viscous relaxation on an icy crust that is thin compared to the crater diameter or on a thick icy crust in which viscosity increases with depth could not produce this crater morphology and would result in the more rapid relaxation of small craters rather than large craters. The results of this study suggest that more detailed analysis of relaxing impact crater morphology may resolve the rate of viscosity decrease with depth and so provide evidence on the interior thermal evolution of icy planetary bodies.  相似文献   

20.
Studies of element abundances and values of D/H in the atmospheres of the outer planets and Titan support a two-step model for the formation of these bodies. This model suggests that the dimensions of Uranus provide a good index for the sensitivity required to detect planets around other stars. The high proportion of N2 on the surfaces of Pluto and Triton indicates that this gas was the dominant reservoir of nitrogen in the early solar nebula. It should also be abundant on pristine comets. There is evidence that some of these comets may well have brought a large store of volatiles to the inner planets, while others were falling into the sun. In other systems, icy planetesimals falling into stars should reveal themselves through high values of D/H.Paper presented at the Conference on Planetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.  相似文献   

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