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1.
F.P. Fanale 《Icarus》1976,28(2):179-202
Observations of Mars and cosmochemical considerations imply that the total inventory of degassed volatiles on Mars is 102 to 103 times that present in Mars' atmosphere and polar caps. The degassed volatiles have been physically and chemically incorporated into a layer of unconsolidated surface rubble (a “megaregolith”) up to 2km thick. Tentative lines of evidence suggest a high concentration (～5g/cm2) of 40 Ar in the atmosphere of Mars. If correct, this would be consistent with a degassing model for Mars in which the Martian “surface” volatile inventory is presumed identical to that of Earth but scaled to Mars' smaller mass and surface area. The implied inventory would be: (40Ar) = 4g/cm2, (H2O) = 1 × 105g/cm2, (CO2) = 7 × 103g/cm2, (N2) = 3 × 102g/cm2, (Cl) = 2 × 103g/cm2, and (S) = 2 × 102g/cm2. Such a model is useful for testing, but differences in composition and planetary energy history may be anticipated between Mars and Earth on theoretical grounds. Also, the model demands huge regolith sinks for the volatiles listed.If the regolith were in physical equilibrium with the atmosphere, as much as 2 × 104g/cm2 of H2O could be stored in it as hard-frozen permafrost, or 5 × 104g/cm2 if equilibrium with the atmosphere were inhibited. Spectral measurements of Martian regolith material and laboratory measurement of weathering kinetics on simulated regolith material suggest large amounts of hydrated iron oxides and clay minerals exist in the regolith; the amount of chemically bound H2O could be from 1 × 104 to 4 × 104g/cm2. In an Earth-analogous model, a 2 km mixed regolith must contain the following concentrations of other volatile-containing compounds by weight: carbonates = 1.5%, nitrates = 0·3%, chlorides = 0.6%, and sulfates = 0.1%. Such concentrations would be undetectable by current Earth-based spectral reflectance measurements, and (except the nitrates) formation of the “required” amounts of these compounds could result from interaction of adsorbed H2O and ice with primary silicates expected on Mars. Most of the CO2 could be physically adsorbed on the regolith.Thus, maximum amounts of H2O and other volatiles which could be stored in the Mars regolith are marginally compatible with those required by an Earth-analogous model, although a lower atmospheric 40Ar concentration and regolith volatile inventory would be easier to reconcile with observational constraints. Differences in the ratios of H2O and other volatiles to 40Ar between surface volatiles on the real Mars and on an Earth-analogous Mars could result from and reflect differences in bulk composition and time history of degassing between Mars and Earth. Models relating Viking-observable parameters, e.g., (40Ar) and (36Ar), to the time history and overall intensity of Mars degassing are given.  相似文献   

2.
Experimental results on fast ion collision with icy surfaces having astrophysical interest are presented. 252Cf fission fragments projectiles were used to induce ejection of ionized material from H2O, CO2, CO, NH3, N2, O2 and Ar ices; the secondary ions were identified by time-of-flight mass spectrometry. It is observed that all the bombarded frozen gas targets emit cluster ions which have the structure XnR±, where X is the neutral ice molecule and R± is either an atomic or a molecular ion. The shape of the positive or negative ion mass spectra is characterized by a decreasing yield as the emitted ion mass increases and is generally described by the sum of two exponential functions. The positive ion water ice spectrum is dominated by the series (H2O)nH3O+ and the negative ion spectrum by the series (H2O)nOH− and (H2O)nO−. The positive ion CO2 ice spectrum is characterized by R+ = C+, O+, CO+, O2+ or CO2+ and the negative one by R− = CO3−. The dominant series for ammonia ice correspond to R+ = NH4+ and to R− = NH2−. The oxygen series are better described by (O3)nOm+ secondary ions where m = 1, 2 or 3. Two positive ion series exist for N2 ice: (N2)nN2+ and (N2)nN+. For argon positive secondary ions, only the (Ar)nAr+ series was observed. Most of the detected molecular ions were formed by one-step reactions. Ice temperature was varied from ∼20 K to complete sublimation.  相似文献   

3.
The calculation of number densities of CO2, H2O and N2 photolysis products was carried out for the Martian atmosphere at heights up to 60 km. The ozone distributed in the atmosphere as a layer of 10 km width with [O3] max = 2.5 × 109 cm3 at height of 35 km which agree well with the results of u.v. observations on the evening terminator from the Mars-5 satellite. The calculated densities of O2, CO and H2O are also in good agreement with the measured data. The eddy diffusion coefficient is equal to 3 × 106 in the troposphere (h ? 30 km) and 108 cm2 s?1 above 40 km. The dependence of the total ozone content on water vapour amount in the atmosphere is considered; the hypothesis about the influence of water ice aerosol on the ozone formation is proposed to explain the high concentrations of ozone in the morning.  相似文献   

4.
Wet adiabatic atmospheric models are computed for the four Jovian planets. Possible cloud-forming condensates considered are H2O ice, aqueous NH3 solution, NH4SH, and solid NH3, CH4, and Ar. Some techniques for computer calculation of condensation in a multiphase system of variable composition are discussed. Nominal models are computed for all four-planets, and the effects of variations in composition and different pressure-temperature regimes are investigated in detail for Jupiter. The meaning of the calculated cloud densities and their relation to the actual densities are discussed. The computed atmospheric profiles represent average conditions, subject to considerable local variations.  相似文献   

5.
We have quantitatively studied, by infrared absorption spectroscopy, the CO/CO2 molecular number ratio after ion irradiation of ices and mixtures containing astrophysically relevant species such as CO, CO2, H2O, CH4, CH3OH, NH3, O2, and N2 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/CO2 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/CO2 ratio in several astrophysical scenarios such as planetary icy surfaces and ice mantles on grains in the interstellar medium. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

6.
Denis Lacelle  David Fisher 《Icarus》2008,197(2):458-469
In this study, various approaches that can potentially distinguish between vapor- and liquid-derived ground ice in the martian regolith (petrography, geochemistry, stable OH isotopes, CO2O2N2Ar gas composition) are examined using terrestrial ground ice examples. Although the stable OH isotope composition ratios can distinguish between vapor- and liquid-derived terrestrial ground ice, there might be to much mixing between the various water reservoirs on Mars to effectively use it, and, like on Earth, petrographic and geochemical approaches need to be complemented with additional supporting evidences. Of the different approaches currently being employed to determine the origin of terrestrial massive ground ice and icy sediments, it is the concentration of CO2 and the O2/Ar, N2/Ar and N2/O2 ratios of air entrapped in the ice that has proven to be the less ambiguous and most discriminatory. This is because the molar ratios of atmospheric gases change during their dissolution in water due to differences in their relative solubilities, thus providing distinctive ratios for the dissolved gases. The gas composition of air entrapped in the ice not only distinguishes between vapor- and liquid-derived ground ice, but any deviation from the theoretical dissolved values can provide insights into potential physical and biological processes operating in the subsurface, a key component for astrobiology.  相似文献   

7.
Models are developed for the photochemistry of a CO2H2ON2 atmosphere on Mars and estimates are given for the concentrations of N, NO, NO2, NO3, N2O5, HNO2, HNO3, and N2O as a function of altitude. Nitric oxide is the most abundant form of odd nitrogen, present with a mixing ratio relative to CO2 of order 10?8. Deposition rates for nitrite and nitrate minerals could be as large as 3× 105 N equivalent atoms cm?2 sec?1 under present conditions and may have been higher in the past.  相似文献   

8.
The absolute reaction cross sections and reaction rate coefficients as a function of photoionisation energy for 25 ion-molecule reactions (charge transfer reactions except for one) have been measured between the most abundant species present as ions or neutral in the Mars, Venus and Earth ionospheres: O2, N2, NO, CO, Ar and CO2.This study shows the strong influence of electronic as well as vibrational internal energy on most ion-molecule reactions. In particular endothermic charge transfer reactions are driven by electronic excitation of O2+ and NO+ ions in their a4Πu and a3Σ+ metastable states, respectively. Moreover, it is shown that lifetimes of these metastable states are sufficient to survive the mean free path in the lowest part of ionospheres and therefore express their enhanced reactivity. The reactions of O2+ with NO as well as the reactions of CO2+ with NO, O2, CO and to a less extent N2 are driven by vibrational excitation. N2+ and CO+ reactions vary much less with photon energy than the other ones, except for the case of reactions with Ar. The effects of the molecular ion internal energy content on their reactivity must be included in the ionospheric models for most of the reactions investigated in the present work. It is also the case for the effect of collision energy on the CO++M reactions as we expect that a significant proportion of these CO+ could be produced with translational energy by dissociation of doubly charged CO22+, in particular in the Mars ionosphere. Recommended effective rate constant values are given as a function of VUV photon energy.  相似文献   

9.
Radiation synthesis has been proposed as a mechanism for changing the nature of the outer few meters of ice in a comet stored 4.6 billion years in the Oort cloud and may explain some of the differences observed between new and more evolved comets. Cometary-type ice mixtures were studied in a laboratory experiment designed to approximately simulate the expected temperature, pressure, and radiation environment of the interstellar Oort cloud region. The 2.5- to 15-μm infrared absorption features of thin ice films were analyzed near 20°K before and after 1 MeV proton irradiation. Various ice mixtures included the molecules H2O, NH3, CH4, N2, C3H8, CO, and CO2. All experiments confirm the synthesis of new molecular species in solid phase mixtures at 20°K. The synthesized molecules, identified by their infrared signatures, are C2H6, CO2, CO, N2O, NO, and CH4 (weak). Synthesized molecules, identified by gas chromatographic (GC) analysis of the volatile fraction of the warmed irradiated ice mixture, are C2H4 or C2H6, and C3H8. When CH4 is present in the irradiated ice mixture, long-chained volatile hydrocarbons and CO2 are synthesized along with high-molecular-weight carbon compounds present in the room temperature residue. Irradiated mixtures containing CO and H2O synthesize CO2 and those CO2 and H2O synthesize CO. Due to radiation synthesis, ～1% of the ice was converted into a nonvolatile residue containing complicated carbon compounds not present in blank samples. These results suggest that irrespective of the composition of newly accreted comets, initial molecular abundances can be altered and new species created as a result of radiation synthesis. Irradiated mixtures exhibited thermoluminescence and pressure enhancements during warming; these phenomena suggest irradiation synthesis of reactive species. Ourbursts in new comets resulting from similar radiation induced exothermic activity would be expected to occur beginning at distances of the order of 100 AU.  相似文献   

10.
The physical adsorption energy,E, of hydrogen molecules on various substrates at temperatures between 5 and 30 K and at the lowest practicable gas densities has been measured. Values ofE/k are for condensed CO 340 K, CO2 800 K, H2O 850 K and for ‘dirty’ graphite 980 K and ‘dirty’ copper 800 K. From these measurements temperature ranges in which H atoms might combine on the surface to form H2 molecules are estimated. Duley has discussed the formation and composition of condensed gas mantles on interstellar grains. The effects of such mantles in promoting and poisoning hydrogen molecule formation are discussed.  相似文献   

11.
New experimental techniques have yielded several thermal energy vibrational quenching rate constants for O2+(v). Rates for quenching of O2+(v = 1) by O2, N2, Ar, CO2, H2, and CH4 are 3(?10), 2(?12), 1(?12), 1(?10), 2.5(?12), and 6(?10) cm3s?1 at 300 K. The quenching is somewhat faster for O2+(v = 2). The triatomic ions CO2+, NO2+, N2O+, SO2+, and H2O+ are all vibrationally deexcited with an efficiency greater than 10?3 in Ar or Ne collisions. A theoretical rationalization of the experimental results leads to the prediction that vibrational quenching in planetary atmospheres will generally be efficient, k > 1(?12) cm3s?1 for almost all ion and neutral gas pairs.  相似文献   

12.
In this work we present the results of a series of laboratory experiments performed to obtain the density and the real part of the refractive index of binary mixtures of ices of astrophysical interest. Densities of CO2:CH4 mixtures obey the expected weighted mean and the other binary mixtures have densities up to 20% lower than expected. Refractive index for all the binary mixtures deviates up to 5% from the theoretical, obtaining higher values than expected for CO2:CH4 and lower values than predicted for CO2:N2 and CH4:N2.  相似文献   

13.
Long-term spectroscopic observations of the O2 dayglow at 1.27 μm result in a map of the latitudinal and seasonal behavior of the dayglow intensity for the full martian year. The O2 dayglow is a sensitive tracer of Mars' photochemistry, and this map reflects variations of Mars' photochemistry at low and middle latitudes. It may be used to test photochemical models. Long-term observations of the CO mixing ratio have been also combined into the seasonal-latitudinal map. Seasonal and latitudinal variations of the mixing ratios of CO and the other incondensable gases (N2, Ar, O2, and H2) discovered in our previous work are caused by condensation and sublimation of CO2 to and from the polar regions. They reflect dynamics of the atmosphere and polar processes. The observed map may be used to test global circulation models of the martian atmosphere. The observed global abundances of CO are in reasonable agreement with the predicted variations with the 11-year solar cycle. Despite the perfect observing conditions, methane has not been detected using the IRTF/CSHELL with a 3σ upper limit of 14 ppb. This upper limit does not rule out the value of 10 ppb observed using the Canada-France-Hawaii Telescope and the Mars Express Planetary Fourier Spectrometer.  相似文献   

14.
The composition of the atmosphere is regulated by biological activity on a variety of time scales. Global biogeochemical cycles of nitrogen, carbon and sulfur are discussed with an emphasis on N2O, NO, CO2, CH4 and SO2. It is argued that Man is a major influence on the budget of these gases. His influence is attributed primarily to use of fossil fuels, to various aspects of agriculture and to the disposal of human and animal waste.  相似文献   

15.
SCIAMACHY (SCanning Imaging Absorption spectrometer for Atmospheric CHartographY) is a space based spectrometer designed to measure sunlight transmitted, reflected and scattered by the Earth atmosphere or surface. It is a contribution to the Envisat-1 satellite to be launched in late 1999.SCIAMACHY measurements will provide amounts and distribution of 03, BrO, OCl0, ClO, S02, H2CO, N02, CO, CO2, CH4, H2O, N20, pressure, temperature, aerosol, radiation, cloud cover and cloud top height from atmospheric measurements in nadir, limb and occultation geometry.By the combination of the near simultaneous limb and nadir observations SCIAMACHY is one of a limited number of instruments which is able to detect tropospheric column amounts of 03, N02, CO, CH4, H2O, N20, S02, H2CO, and BrO down to the planetary boundary layer under cloud free conditions.  相似文献   

16.
One-dimensional radial models of the chemistry in cometary comae have been constructed for heliocentric distances ranging from 2 to 0.125 AU. The coma's opacity to solar radiation is included and photolytic reaction rates are calculated. A parent volatile mixture similar to that found in interstellar molecular clouds is assumed. Profiles through the coma of number density and column density are presented for H2O, OH, O, CN, C2, C3, CH, and NH2. Whole-coma abundances are presented for NH2, CH, C2, C3, CN, OH, CO+, H2O+, CH+, N2+, and CO2+.  相似文献   

17.
The trapping and release of H2, CO, CO2, CH4, Ar, Ne, and N2 by amorphous water ice was studied experimentally under dynamic conditions, at low temperatures starting at 16°K, with gas pressure of 5 × 10?8?10?6 Torr. CO, CH4, Ar, and N2 were found to be released in three or four distinct temperature ranges, each resulting from a different trapping mechanism: (a) 30–55°K, where the gas frozen on the water ice evaporates; (b) 135–155°K, where gas is squeezed out of the water ice during the transformation of amorphous ice to cubic ice; (c) 165–190°K, where gas and water are released simultaneously, probably by the evaporation of a clathrate hydrate, and, occasionally (d) 160–175°K, where deeply buried gas is released during the transformation of cubic ice to hexagonal ice. If the third range is indeed due to clathrate formation, CO was found to form this compound. CO2 did not form a clathrate under the experimental conditions. Excess hydrogen did not affect the occlusion of other gases. Hydrogen itself was trapped only at 16°K. Neon was not trapped at 25°K. With cubic ice, the only trapping mechanism is freezing of gas on the ice surface. No fractionation between the gas phase and the ice was observed with a mixture of CO and Ar. Massive ejection of ice grains was observed during the evaporation of the gas in three (a,c,d) out of the four ranges. The experimental results are used to explain several cometary phenomena, especially those occurring at large heliocentric distances, and are applied also to Titan's atmospheric composition and to the possible ejection of ice grains from Enceladus.  相似文献   

18.
《New Astronomy Reviews》2000,44(4-6):329-334
Heavy element abundances derived from high-quality ground-based and Hubble Space Telescope (HST) spectroscopic observations of low-metallicity blue compact galaxies (BCGs) with oxygen abundances 12+log O/H between 7.1 and 8.3 are discussed. None of the heavy element-to-oxygen abundance ratios studied here (C/O, N/O, Ne/O, Si/O, S/O, Ar/O, Fe/O) depend on oxygen abundance for BCGs with 12+log O/H≤7.6 (Z≤Z⊙/20). This constancy implies that all these heavy elements have a primary origin and are produced by the same massive (M≥10 M⊙) stars responsible for O production. The dispersion of the C/O and N/O ratios in these galaxies is found to be remarkably small, being only ±0.03 dex and ±0.02 dex respectively. This very small dispersion is strong evidence against any time-delayed production of C and primary N in the lowest-metallicity BCGs, and hence against production of these elements by intermediate-mass (3 M⊙≤M≤9 M⊙) stars at very low metallicities, as commonly thought.In higher metallicity BCGs (7.6<12+log O/H<8.2), the Ne/O, Si/O, S/O, Ar/O and Fe/O abundance ratios retain the same constant value they had at lower metallicities. By contrast, there is an increase of the C/O and N/O ratios along with their dispersions at a given O. We interpret this increase as due to the additional contribution of C and primary N production in intermediate-mass stars, on top of that by high-mass stars. BCGs show the same O/Fe overabundance with respect to the Sun (∼0.4 dex) as galactic halo stars, suggesting the same chemical enrichment history.  相似文献   

19.
Spectroscopic observations of four planetary nebulae (PNe) with emission-line central stars of different spectral types are presented: Cn 1-5, Pe 1-1, NGC 5873, and M1-19. The interstellar extinction, physical conditions (n e , T e ), and abundances of several elements (He, N, O, Ne, S, Ar, Cl) have been determined for all nebulae. The nebula Cn 1–5 with fairly high abundances of helium and nitrogen is shown to belong to type I PNe. Possible variability of the intensities of low-excitation emission lines in NGC 5873 has been found; it can be related to variations of the stellar wind from the central star. The measured α-element abundance ratios (S/O, Ne/O, Ar/O, Cl/O) are in good agreement with those typical of HII regions.  相似文献   

20.
A. Bar-Nun  G. Notesco 《Icarus》2007,190(2):655-659
Recent attempts using high resolution spectra to detect N+2 in several comets were unsuccessful [Cochran, A.L., Cochran, W.D., Baker, E.S., 2000. Icarus 146, 583-593; Cochran, A.L., 2002. Astrophys. J. 576, L165-L168]. The upper limits on N+2 in comparison with the positively detected CO+ for Comets C/1995 O1 Hale-Bopp, 122P/1995 S1 de Vico and 153P/2002 C1 Ikeya-Zhang range between . Ar was not detected in three recent comets [Weaver, H.A., Feldman, P.D., Combi, M.R., Krasnopolsky, V., Lisse, C.M., Shemansky, D.E., 2002. Astrophys. J. 576, L95-L98], with upper limits of Ar/CO<(3.4-7.8)×10−2 for Comets C/1999 T1 McNaught-Hartley, C/2001 A2 LINEAR and C/2000 WM1 LINEAR. The Ar detected by Stern et al. [Stern, S.A., Slater, D.C., Festou, M.C., Parker, J.Wm., Gladstone, G.R., A'Hearn, M.F., Wilkinson, E., 2000. Astrophys. J. 544, L169-L172] for Comet C/1995 O1 Hale-Bopp, gives a ratio Ar/CO=7.25×10−2, which was not confirmed by Cosmovici et al. [Cosmovici, C.B., Bratina, V., Schwarz, G., Tozzi, G., Mumma, M.J., Stalio, R., 2006. Astrophys. Space Sci. 301, 135-143]. Trying to solve the two problems, we studied experimentally the trapping of N2+CO+Ar in amorphous water ice, at 24-30 K. CO was found to be trapped in the ice 20-70 times more efficiently than N2 and with the same efficiency as Ar. The resulting Ar/CO ratio of 1.2×10−2 is consistent with Weaver et al.'s [Weaver, H.A., Feldman, P.D., Combi, M.R., Krasnopolsky, V., Lisse, C.M., Shemansky, D.E., 2002. Astrophys. J. 576, L95-L98] non-detection of Ar. However, with an extreme starting value for N2/CO = 0.22 in the region where the ice grains which agglomerated to produce comet nuclei were formed, the expected N2/CO ratio in the cometary ice should be 6.6×10−3, much higher than its non-detection limit.  相似文献   

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