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1.
We report laboratory studies on the 0.8 MeV proton irradiation of ices composed of sulfuric acid (H2SO4), sulfuric acid monohydrate (H2SO4·H2O), and sulfuric acid tetrahydrate (H2SO4·4H2O) between 10 and 180 K. Using infrared spectroscopy, we identify the main radiation products as H2O, SO2, (S2O3)x, H3O+, , and . At high radiation doses, we find that H2SO4 molecules are destroyed completely and that H2SO4·H2O is formed on subsequent warming. This hydrate is significantly more stable to radiolytic destruction than pure H2SO4, falling to an equilibrium relative abundance of 50% of its original value on prolonged irradiation. Unlike either pure H2SO4 or H2SO4·H2O, the loss of H2SO4·4H2O exhibits a strong temperature dependence, as the tetrahydrate is essentially unchanged at the highest irradiation temperatures and completely destroyed at the lowest ones, which we speculate is due to a combination of radiolytic destruction and amorphization. Furthermore, at the lower temperatures it is clear that irradiation causes the tetrahydrate spectrum to transition to one that closely resembles the monohydrate spectrum. Extrapolating our results to Europa’s surface, we speculate that the variations in SO2 concentrations observed in the chaotic terrains are a result of radiation processing of lower hydration states of sulfuric acid and that the monohydrate will remain stable on the surface over geological times, while the tetrahydrate will remain stable in the warmer regions but be destroyed in the colder regions, unless it can be reformed by other processes, such as thermal reactions induced by diurnal cycling. 相似文献
2.
Infrared spectra and radiation chemical behavior of N2-dominated ices relevant to the surfaces of Triton and Pluto are presented. This is the first systematic IR study of proton-irradiated N2-rich ices containing CH4 and CO. Experiments at 12 K show that HCN, HNC, and diazomethane (CH2N2) form in the solid phase, along with several radicals. NH3 is also identified in irradiated N2 + CH4 and N2 + CH4 + CO. We show that HCN and HNC are made in irradiated binary ice mixtures having initial N2/CH4 ratios from 100 to 4, and in three-component mixtures have an initial N2/(CH4 + CO) ratio of 50. HCN and HNC are not detected in N2-dominated ices when CH4 is replaced with C2H6, C2H2, or CH3OH.The intrinsic band strengths of HCN and HNC are measured and used to calculate G(HCN) and G(HNC) in irradiated N2 + CH4 and N2 + CH4 + CO ices. In addition, the HNC/HCN ratio is calculated to be ∼1 in both icy mixtures. These radiolysis results reveal, for the first time, solid-phase synthesis of both HCN and HNC in N2-rich ices containing CH4.We examine the evolution of spectral features due to acid-base reactions (acids such as HCN, HNC, and HNCO and a base, NH3) triggered by warming irradiated ices from 12 K to 30-35 K. We identify anions (OCN−, CN−, and N3−) in ices warmed to 35 K. These ions are expected to form and survive on the surfaces of Triton and Pluto. Our results have astrobiological implications since many of these products (HCN, HNC, HNCO, NH3, NH4OCN, and NH4CN) are involved in the syntheses of biomolecules such as amino acids and polypeptides. 相似文献
3.
The goal of this study was to explore prebiotic chemistry in a range of plausible early Earth and Mars atmospheres. To achieve this laboratory continuous flow plasma irradiation experiments were performed on N2/H2/CO/CO2 gas mixtures chosen to represent mildly reducing early Earth and Mars atmospheres derived from a secondary volcanic outgassing of volatiles in chemical equilibrium with magmas near present day oxidation state. Under mildly reducing conditions (91.79% N2, 5.89% H2, 2.21% CO, and 0.11% CO2), simple nitriles are produced in the gas phase with yield (G in molecules per 100 eV), for the key prebiotic marker molecule HCN at G∼1×10−3 (0.1 nmol J−1). In this atmosphere localized HCN concentrations possibly could approach the 10−2 M needed for HCN oligomerization. Yields under mildly oxidizing conditions (45.5% N2, 0.1% H2, 27.2% CO, 27.2% CO2) are significantly less as expected, with HCN at G∼3×10−5 (). Yields in a Triton atmosphere which can be plausibly extrapolated to represent what might be produced in trace CH4 conditions (99.9% N2, 0.1% CH4) are significant with HCN at G∼1×10−2 (1 nmol J−1) and tholins produced. Recently higher methane abundance atmospheres have been examined for their greenhouse warming potential, and higher abundance hydrogen atmospheres have been proposed based on a low early Earth exosphere temperature. A reducing (64.04% N2, 28.8% H2, 3.60% CO2, and 3.56% CH4), representing a high CH4 and H2 abundance early Earth atmosphere had HCN yields of G∼5×10−3 (0.5 nmol J−1). Tholins generated in high methane hydrogen gas mixtures is much less than in a similar mixture without hydrogen. The same mixture with the oxidizing component CO2 removed (66.43% N2, 29.88% H2, 0% CO2, and 3.69% CH4) had HCN yields of G∼1×10−3 (0.1 nmol J−1) but more significant tholin yields. 相似文献
4.
A two-dimensional kinetic model calculation for the water group species (H2O, H2, O2, OH, O, H) in Europa's atmosphere is undertaken to determine its basic compositional structure, gas escape rates, and velocity distribution information to initialize neutral cloud model calculations for the most important gas tori. The dominant atmospheric species is O2 at low altitudes and H2 at higher altitudes with average day-night column densities of 4.5×1014 and 7.7×1013 cm−2, respectively. H2 forms the most important gas torus with an escape rate of ∼2×1027 s−1 followed by O with an escape rate of ∼5×1026 s−1, created primarily as exothermic O products from O2 dissociation by magnetospheric electrons. The circumplanetary distributions of H2 and O are highly peaked about the satellite location and asymmetrically distributed near Europa's orbit about Jupiter, have substantial forward clouds extending radially inward to Io's orbit, and have spatially integrated cloud populations of 4.2×1033 molecules for H2 and 4.0×1032 atoms for O that are larger than their corresponding populations in Europa's local atmosphere by a factor of ∼200 and ∼1000, respectively. The cloud population for H2 is a factor of ∼3 times larger than that for the combined cloud population of Io's O and S neutral clouds and provides the dominant neutral population beyond the so-called ramp region at 7.4-7.8 RJ in the plasma torus. The calculated brightness of Europa's O cloud on the sky plane is very dim at the sub-Rayleigh level. The H2 and O tori provide a new source of europagenic molecular and atomic pickup ions for the thermal plasma and introduce a neutral barrier in which new plasma sinks are created for the cooler iogenic plasma as it is transported radially outward and in which new sinks are created to alter the population and pitch angle distribution of the energetic plasma as it is transported radially inward. The europagenic instantaneous pickup ion rates are peaked at Europa's orbit, dominate the iogenic pickup ion rates beyond the ramp region, and introduce new secondary plasma source peaks in the solution of the plasma transport problem. The H2 torus is identified as the unknown Europa gas torus that creates both the observed loss of energetic H+ ions at Europa's orbit and the corresponding measured ENA production rate for H. 相似文献
5.
Vladimir A. Krasnopolsky 《Icarus》2011,215(1):197-203
The vertical profile of H2SO4 vapor is calculated using current atmospheric and thermodynamic data. The atmospheric data include the H2O profiles observed at 70-112 km by the SOIR solar occultations, the SPICAV-UV profiles of the haze extinction at 220 nm, the VeRa temperature profiles, and a typical profile of eddy diffusion. The thermodynamic data are the saturated vapor pressures of H2O and H2SO4 and chemical potentials of these species in sulfuric acid solutions. The calculated concentration of sulfuric acid in the cloud droplets varies from 85% at 70 km to a minimum of 70% at 90 km and then gradually increasing to 90-100% at 110 km. The H2SO4 vapor mixing ratio is ∼10−12 at 70 and 110 km with a deep minimum of 3 × 10−18 at 88 km. The H2O-H2SO4 system matches the local thermodynamic equilibrium conditions up to 87 km. The column photolysis rate of H2SO4 is 1.6 × 105 cm−2 s−1 at 70 km and 23 cm−2 s−1 at 90 km. The calculated abundance of H2SO4 vapor at 90-110 km and its photolysis rate are smaller than those presented in the recent model by Zhang et al. (Zhang, X., Liang, M.C., Montmessin, F., Bertaux, J.L., Parkinson, C., Yung, Y.L. [2010]. Nat. Geosci. 3, 834-837) by factors of 106 and 109, respectively. Assumptions of 100% sulfuric acid, local thermodynamic equilibrium, too warm atmosphere, supersaturation of H2SO4 (impossible for a source of SOX), and cross sections for H2SO4·H2O (impossible above the pure H2SO4) are the main reasons of this huge difference. Significant differences and contradictions between the SPICAV-UV, SOIR, and ground-based submillimeter observations of SOX at 70-110 km are briefly discussed and some weaknesses are outlined. The possible source of high altitude SOX on Venus remains unclear and probably does not exist. 相似文献
6.
Jon M. JenkinsMarc A. Kolodner Bryan J. ButlerShady H. Suleiman Paul G. Steffes 《Icarus》2002,158(2):312-328
A multi-wavelength radio frequency observation of Venus was performed on April 5, 1996, with the Very Large Array to investigate potential variations in the vertical and horizontal distribution of temperature and the sulfur compounds sulfur dioxide (SO2) and sulfuric acid vapor (H2SO4(g)) in the atmosphere of the planet. Brightness temperature maps were produced which feature significantly darkened polar regions compared to the brighter low-latitude regions at both observed frequencies. This is the first time such polar features have been seen unambiguously in radio wavelength observations of Venus. The limb-darkening displayed in the maps helps to constrain the vertical profile of H2SO4(g), temperature, and to some degree SO2. The maps were interpreted by applying a retrieval algorithm to produce vertical profiles of temperature and abundance of H2SO4(g) given an assumed sub-cloud abundance of SO2. The results indicate a substantially higher abundance of H2SO4(g) at high latitudes (above 45°) than in the low-latitude regions. The retrieved temperature profiles are up to 25 K warmer than the profile obtained by the Pioneer Venus sounder probe at altitudes below 40 km (depending on location and assumed SO2 abundance). For 150 ppm of SO2, it is more consistent with the temperature profile obtained by Mariner 5, extrapolated to the surface via a dry adiabat. The profiles obtained for H2SO4(g) at high latitudes are consistent with those derived from the Magellan radio occultation experiments, peaking at around 8 ppm at an altitude of 46 km and decaying rapidly away from that altitude. At low latitudes, no significant H2SO4(g) is observed, regardless of the assumed SO2 content. This is well below that measured by Mariner 10 (Lipa and Tyler 1979, Icarus39, 192-208), which peaked at ∼14 ppm near 47 km. Our results favor ≤100 ppm of SO2 at low latitudes and ≤50 ppm in polar regions. The low-latitude value is statistically consistent with the results of Bézard et al. (1983, Geophs. Res. Lett.20, 1587-1590), who found that a sub-cloud SO2 abundance of 130±40 ppm best matched their observations in the near-IR. The retrieved temperature profile and higher abundance of H2SO4(g) in polar regions are consistent with a strong equatorial-to-polar, cloud-level flow due to a Hadley cell in the atmosphere of Venus. 相似文献
7.
Fractional abundances of stratospheric negative ions are for the first time explicitly reported. The measurements made by balloon-borne ion mass spectrometers also rely on recent studies of electric field induced collisional dissociation of negative cluster ions conducted at our laboratory. These indicate that the negative ion composition measurements around 36 km conducted by our group do not suffer from any significant dissociation. The new composition data support ion identifications NO3?(HNO3)b and HSO4?(H2SO4)c(HNO3)d and the underlying ion reactions propo previously. Moreover, it is found that HSO4?(H2SO4)g-ions appear to be particularly stable and that H2SO4-association is very fast. Implications of the ion composition data for ion processes are discussed. 相似文献
8.
J.L. McLain 《Planetary and Space Science》2009,57(13):1642-39
A study has been made using a variable temperature flowing afterglow Langmuir probe technique (VT-FALP) to determine the equilibrium temperature dependencies of the dissociative electron-ion recombination of the protonated cyanide ions (RCNH+, where R=H, CH3 and C2H5) and their symmetrical proton-bound dimers (RCNH+NCR). The power law temperature dependencies of the recombination coefficients, αe, over the temperature range 180 to 600 K for the protonated ions are αe(T)(cm3 s−1)=3.5±0.5×10−7 (300/T)1.38 for HCNH+, αe(T)=3.4±0.5×10−7 (300/T)1.03 for CH3CNH+, and αe(T)=4.6±0.7×10−7 (300/T)0.81 for CH3CH2CNH+. The equivalent values for the proton-bound dimers are αe(T)(cm3 s−1)=2.4±0.4×10−6(300/T)0.5 for (HCN)2H+ to αe(T)=2.8±0.4×10−6(300/T)0.5 for (CH3CN)2H+, and αe(T)=2.3±0.3×10−6(300/T)0.5 for (CH3CH2CN)2H+. The relevance of these data to molecular synthesis in the interstellar medium and the Titan ionosphere are discussed. 相似文献
9.
Volcanism has been a major process during most of the geologic history of Mars. Based on data collected from terrestrial basaltic eruptions, we assume that the volatile content of martian lavas was typically ∼0.5 wt.% water, ∼0.7 wt.% carbon dioxide, ∼0.14 wt.% sulfur dioxide, and contained several other important volatile constituents. From the geologic record of volcanism on Mars we find that during the late Noachian and through the Amazonian volcanic degassing contributed ∼0.8 bar to the martian atmosphere. Because most of the outgassing consisted of greenhouse gases (i.e., CO2 and SO2) warmer surface temperatures resulting from volcanic eruptions may have been possible. Our estimates suggest that ∼1.1 × 1021 g (∼8 ± 1 m m−2) of juvenile water were released by volcanism; slightly more than half the amount contained in the north polar cap and atmosphere. Estimates for released CO2 (1.6 × 1021 g) suggests that a large reservoir of carbon dioxide is adsorbed in the martian regolith or alternatively ∼300 cm cm−2 of carbonates may have formed, although these materials would not occur readily in the presence of excess SO2. Up to ∼120 cm cm−2 (2.2 × 1020 g) of acid rain (H2SO4) may have precipitated onto the martian surface as the result of SO2 degassing. The hydrogen flux resulting from volcanic outgassing may help explain the martian atmospheric D/H ratio. The amount of outgassed nitrogen (∼1.3 mbar) may also be capable of explaining the martian atmospheric 15N/14N ratio. Minor gas constituents (HF, HCl, and H2S) could have formed hydroxyl salts on the surface resulting in the physical weathering of geologic materials. The amount of hydrogen fluoride emitted (1.82 × 1018 g) could be capable of dissolving a global layer of quartz sand ∼5 mm thick, possibly explaining why this mineral has not been positively identified in spectral observations. The estimates of volcanic outgassing presented here will be useful in understanding how the martian atmosphere evolved over time. 相似文献
10.
Spectra of Europa, Ganymede, and Callisto reveal surfaces dominated by frozen water, hydrated materials, and minor amounts of SO2, CO2, and H2O2. These icy moons undergo significant bombardment by jovian magnetospheric radiation (protons, electrons, and sulfur and oxygen ions) which alters their surface compositions. In order to understand radiation-induced changes on icy moons, we have measured the mid-infrared spectra of 0.8 MeV proton-irradiated SO2, H2S, and H2O-ice mixtures containing either SO2 or H2S. Samples with H2O/SO2 or H2O/H2S ratios in the 3-30 range have been irradiated at 86, 110, and 132 K, and the radiation half-lives of SO2 and H2S have been determined. New radiation products include the H2S2 molecule and HSO−3, HSO−4, and SO2−4 ions, all with spectral features that make them candidates for future laboratory work and, perhaps, astronomical observations. Spectra of both unirradiated and irradiated ices have been recorded as a function of temperature, to examine thermal stability and phase changes. The formation of hydrated sulfuric acid in irradiated ice mixtures has been observed, along with the thermal evolution of hydrates to form pure sulfuric acid. These laboratory studies provide fundamental information on likely processes affecting the outer icy shells of Europa, Ganymede, and Callisto. 相似文献
11.
A 1-D collisional Monte Carlo model of Europa's atmosphere is described in which the sublimation and sputtering sources of H2O molecules and their molecular fragments are accounted for as well as the radiolytically produced O2. Dissociation and ionization of H2O and O2 by magnetospheric electron, solar UV-photon and photo-electron impact, and collisional ejection from the atmosphere by the low-energy plasma are taken into account. Reactions with the surface are discussed, but only adsorption and atomic oxygen recombination are included in this model. The size of the surface-bounded oxygen atmosphere of Europa is primarily determined by a balance between atmospheric sources from irradiation of the satellite's icy surface by the high-energy magnetospheric charged particles and atmospheric losses from collisional ejection by the low-energy plasma, photo- and electron-impact dissociation, and ionization and pick-up from the surface-bounded atmosphere. A range of sources rates for O2 to H2O are used with a larger oxygen-to-water ratio than suggested by laboratory measurements in order to account for differences in adsorption onto grains in the regolith. These calculations show that the atmospheric composition is determined by both the water and oxygen photochemistry in the near-surface region, escape of suprathermal oxygen and water into the jovian system, and the exchange of radiolytic water products with the porous regolith. For the electron impact ionization rates used, pick-up ionization is the dominant oxygen loss process, whereas photo-dissociation and atmospheric sputtering are the dominant sources of neutral oxygen for Europa's neutral torus. Including desorption and loss of water enhances the supply of oxygen species to the neutral torus, but hydrogen produced by radiolysis is the dominant source of neutrals for Europa's torus in these models. 相似文献
12.
The newly detected oxygen atmosphere of Europa is modeled by invoking charged particle sputtering with H2O and O2molecules as the main ejecta. The magnetospheric corotating ions could provide the required source strength (∼3 × 1026sec−1) of O2molecules if a fraction (∼20%) of the exospheric ions were recycled to Europa's surface where they produce additional sputtering product. Two exospheric components are expected to form: an extended corona with a size of a few satellite radii which is composed of sputtered molecules in ballistic motion, and a thermal population with a surface density of 108–109cm−3and a scale height of about 20 km. The electron impact ionization of this exosphere would lead to an Io-like interaction with the jovian magnetosphere with a field-aligned Birkeland current of about 5 × 105A. 相似文献
13.
Ices in the solar system are observed on the surface of planets, satellites, comets and asteroids where they are continuously subordinate at particle fluxes (cosmic ions, solar wind and charged particles caught in the magnetosphere of the planets) that deeply modify their physical and structural properties. Each incoming ion destroys molecular bonds producing fragments that, by recombination, form new molecules also different from the original ones. Moreover, if the incoming ion is reactive (H+, On+, Sn+, etc.), it can concur to the formation of new molecules.Those effects can be studied by laboratory experiments where, with some limitation, it is possible to reproduce the astrophysical environments of planetary ices.In this work, we describe some experiments of 15-100 keV H+ and He+ implantation in pure sulfur dioxide (SO2) at 16 and 80 K and carbon dioxide (CO2) at 16 K ices aimed to search for the formation of new molecules. Among other results we confirm that carbonic acid (H2CO3) is formed after H-implantation in CO2, vice versa H-implantation in SO2 at both temperatures does not produce measurable quantity of sulfurous acid (H2SO3). The results are discussed in the light of their relevance to the chemistry of some solar system objects, particularly of Io, the innermost of Jupiter's Galilean satellites, that exhibits a surface very rich in frost SO2 and it is continuously bombarded with H+ ions caught in Jupiter's magnetosphere. 相似文献
14.
Balloon-borne mass spectrometers with extended mass range have been flown during controlled descents. This gave detailed height profiles of stratospheric negative ions between 15 and 34 km. The main ion families were HSO4?(H2SO4)m(HNO3)n and NO3? (HNO3)n Information concerning trace gases is o well as an assessment of the problems of ion fragmentation and contamination. Finally, the data are used to derive information concerning the rate of H2SO4 clustering. 相似文献
15.
Far-IR (25-50 μm, 200-400 cm−1) nadir and limb spectra measured during Cassini's four year prime mission by the Composite InfraRed Spectrometer (CIRS) instrument have been used to determine the abundances of cyanogen (C2N2), methylacetylene (C3H4), and diacetylene (C4H2) in Titan's stratosphere as a function of latitude. All three gases are enriched at northern latitudes, consistent with north polar subsidence. C4H2 abundances agree with those derived previously from mid-IR data, but C3H4 abundances are about 2 times lower, suggesting a vertical gradient or incorrect band intensities in the C3H4 spectroscopic data. For the first time C2N2 was detected at southern and equatorial latitudes with an average volume mixing ratio of 5.5±1.4×10−11 derived from limb data (>3-σ significance). This limb result is also corroborated by nadir data, which give a C2N2 volume mixing ratio of 6±3×10−11 (2-σ significance) or alternatively a 3-σ upper limit of 17×10−11. Comparing these figures with photochemical models suggests that galactic cosmic rays may be an important source of N2 dissociation in Titan's stratosphere. Like other nitriles (HCN, HC3N), C2N2 displays greater north polar relative enrichment than hydrocarbons with similar photochemical lifetimes, suggesting an additional loss mechanism for all three of Titan's main nitrile species. Previous studies have suggested that HCN requires an additional sink process such as incorporation into hazes. This study suggests that such a sink may also be required for Titan's other nitrile species. 相似文献
16.
We report the results from a systematic laboratory investigation on the fundamental properties of hydrous ferric sulfates. The study involves 150 experiments with duration of over 4 years on the stability field and phase transition pathways under Mars relevant environmental conditions for five ferric sulfates: ferricopiapite [Fe4.67(SO4)6(OH)2·20H2O], kornelite [Fe2(SO4)3·7H2O], a crystalline and an amorphous pentahydrated ferric sulfate [Fe2(SO4)3·5H2O], and rhomboclase [FeH(SO4)2·4H2O]. During the processes of phase transitions, we observed the phenomena that reflect fundamental properties of these species and the occurrence of other common hydrous ferric sulfates, e.g. paracoquimbite [Fe2(SO4)3·9H2O]. Based on the results of this set of experiments, we have drown the boundaries of deliquescence zone of five hydrous ferric sulfates and estimated the regions of their stability field in temperature (T) – relative humidity (RH) space. Furthermore, we selected the experimental parameters for a next step investigation, which is to determine the location of the phase boundary between two solid ferric sulfates, kornelite [Fe2(SO4)3·7H2O] and pentahydrated ferric sulfate [Fe2(SO4)3·5H2O]. The experimental observations in ferricopiapite dehydration processes were used to interpret the observed spectral change of Fe-sulfate-rich subsurface soils on Mars after their exposure by the Spirit rover to current martian atmospheric conditions. 相似文献
17.
A spectroscopic search for H2O and CH4 in Comet Kohoutek (1973f) was made using a Pepsios interferometer. No evidence was found for either molecule, allowing us to set an upper limit on their production rates (on about 21 January 1974) of Q(H2O) < 6.2 × 1028 sec?1 and Q(CH4) < 2.0 × 1030 sec?1. If the cometary surface is water-ice, this production rate leads to a product (1 ? A)·(πR02) < 2.2 km2, where A is the Bond albedo, R0 is the nuclear radius, and we assume that all the absorbed solar energy is used to evaporate H2O. 相似文献
18.
The reactivity of C2(X1Σ+g) with simple saturated (CH4, C2H6 and C3H8) and unsaturated (C2H2 and C2H4) hydrocarbons has been studied in the gas phase over the temperature range 24-300 K using the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in a Uniform Supersonic Flow) technique. All reactions have been found to be very rapid in this temperature range and the rate coefficients are typically ?10−10 cm3 molecule−1 s−1 with the exception of methane for which the rate coefficient is one order of magnitude lower: ∼10−11 cm3 molecule−1 s−1. These results have been analyzed in terms of potential destruction sources of C2(X1Σ+g) in the atmospheres of Titan and the Giant Planets. It appears that the rate coefficient of the reaction 1C2 + CH4 should be updated with our new data and that reactions with C2H2, C2H4 and C2H6 should also be included in the existing photochemical models. 相似文献
19.
We have investigated the characteristics of the distribution of neutron exposures (“DNE” hereafter) in the He-shell nucleosynthesis regions in the model of s-process nucleosynthesis in low-mass AGB (Asymptotic Giant Branch) stars in 13C radiatively burning conditions. The result indicates that although the DNE obtained with this model is still approximately exponential, like those of the previous convective s-process scenarios, the relation between the neutron exposure Δτ of each pulse and the mean neutron exposure τ0 is no longer τ0 = −Δτ/ln r, rather, it is now approximately τ0 = −Δτ/ ln{q[1.0020 + 0.6602(r − q) + 4.6125(r − q)2− 10.8962(r − q)3+ 13.9138(r − q)4]} (r is the overlap factor, q is the mass ratio of the 13C shell to the He shell). This formula unifies the stellar model of radiative s-process with the classical model from the angle of DNE. 相似文献
20.
《Icarus》1987,70(2):354-365
Liquid solutions of N2 containing up to one-third CH4 can exist on Triton's surface in regions T > 62.5°K. More generally, subsurface oceans of N2 solution are expected to be stable beneath overlying, thermally insulating, less dense layers of the abundant light hydrocarbon products of radiochemical synthesis: C2H6, C3H8, and C4H10. Cosmic rays are the main source of energy, capable of producing synthesis of organic compounds from N2CH4 solutions on the surface. For baseline Triton models with R = 2500 km, ϱ = 2.1 g cm−3, and Ts = 65 or 55°K, respectively, 4 × 10−3 or 7 × 10−3 erg cm−2 sec−1 (49 or 87% of the total incident flux) is deposited within a few meters below the surface. Using yields from laboratory experiments, we estimate the quantities of products produced: over 4.5 billion years, the cosmic ray flux alone produces 2 to 4 m of organic product, about half of which is C2H6. For ocean depths <250 m, C2H6 will reach its saturation limit and form a surface “slick.” For ocean depths <10 km, all of the other products also oversaturate and exsolve, adding to the surface slick and/or to a denser bottom sediment. Products produced from solid N2CH4 mixtures will accumulate as evaporite deposits because of the rapid volatile transport (of N2 and CH4) over Triton's surface. The complex, reddish organic solid found in laboratory simulations is probably the source of Triton's reddish color. Estimated yields over 4.5 billion years (for 7 × 10−3 erg cm−2 sec−1) are 190 (C2H6), 58 (NH3), 17 (HCN), 3.5 (HN3), 2.5 (C4H10), 0.35 (CH3CN), and 0.14 (C2H5N3) g cm−2. More basic laboratory work on the low-temperature, low-pressure solvent properties and phase equilibria of N2-hydrocarbon systems is clearly needed. 相似文献