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1.
The spatial distribution of N+ in Saturn's magnetosphere obtained from Cassini Plasma Spectrometer (CAPS) data can be used to determine the spatial distribution and relative importance of the nitrogen sources for Saturn's magnetosphere. We first summarize CAPS data from 15 orbits showing the spatial and energy distribution of the nitrogen component of the plasma. This analysis re-enforces our earlier discovery [Smith, H.T., Shappirio, M., Sittler, E.C., Reisenfeld, D., Johnson, R.E., Baragiola, R.A., Crary, F.J., McComas, D.J., Young, D.T., 2005. Geophys. Res. Lett. 32 (14). L14S03] that Enceladus is likely the dominant nitrogen source for Saturn's inner magnetosphere. We also find a sharp enhancement in the nitrogen ion to water ion ratio near the orbit of Enceladus which, we show, is consistent with the presence of a narrow Enceladus torus as described in [Johnson, R.E., Liu, M., Sittler Jr., E.C., 2005. Geophys. Res. Lett. 32. L24201]. The CAPS data and the model described below indicate that N+ ions are a significant fraction of the plasma in this narrow torus. We then simulated the combined Enceladus and Titan nitrogen sources using the CAPS data as a constraint. This simulation is an extension of the model we employed earlier to describe the neutral tori produced by the loss of nitrogen from Titan [Smith, H.T., Johnson, R.E., Shematovich, V.I., 2004. Geophys. Res. Lett. 31 (16). L16804]. We show that Enceladus is the principal nitrogen source in the inner magnetosphere but Titan might account for a fraction of the observed nitrogen ions at the largest distances discussed. We also show that the CAPS data is consistent with Enceladus being a molecular nitrogen source with a nitrogen to water ratio roughly consistent with INMS [Waite, J.H., and 13 colleagues, 2006. Science 311 (5766), 1419-1422], but out-gassing of other nitrogen-containing species, such as ammonia, cannot be ruled out. 相似文献
2.
We describe a direct simulation Monte Carlo (DSMC) model of Enceladus’ neutral cloud and compare its results to observations of OH and O orbiting Saturn. The OH and O are observed far from Enceladus (at 3.95 RS), as far out as 25 RS for O. Previous DSMC models attributed this breadth primarily to ion/neutral scattering (including charge exchange) and molecular dissociation. However, the newly reported O observations and a reinterpretation of the OH observations (Melin, H., Shemansky, D.E., Liu, X. [2009] Planet. Space Sci., 57, 1743-1753, PS&S) showed that the cloud is broader than previously thought. We conclude that the addition of neutral/neutral scattering (Farmer, A.J. [2009] Icarus, 202, 280-286), which was underestimated by previous models, brings the model results in line with the new observations. Neutral/neutral collisions primarily happen in the densest part of the cloud, near Enceladus’ orbit, but contribute to the spreading by pumping up orbital eccentricity. Based on the cloud model presented here Enceladus maybe the ultimate source of oxygen for the upper atmospheres of Titan and Saturn. We also predict that large quantities of OH, O and H2O bombard Saturn’s icy satellites. 相似文献
3.
Prasad C. Debi 《Earth, Moon, and Planets》1995,71(1-2):65-71
The Alfvén's critical ionization velocity (CIV) have been observed in a number of laboratory and space experiments. In the Io-torus system, relative velocity of the plasma species in the torus with respect to the neutral species in the Io's atmosphere and neutral cloud exceeds the critical velocity required for CIV. Townsand condition is satisfied up to 6r
io
, in the neutral cloud when Io passes through the torus. In this paper it is shown that during the passage of Io through the plasma torus, apart from critical velocity and Townsand condition, a number of other requirements are also satisfied. Therefore, it is concluded that, the CIV mechanism must play an important role in ionizing the neutral cloud and enriching the plasma torus. 相似文献
4.
Tidal heating in Enceladus 总被引：1，自引：0，他引：1
The heating in Enceladus in an equilibrium resonant configuration with other saturnian satellites can be estimated independently of the physical properties of Enceladus. We find that equilibrium tidal heating cannot account for the heat that is observed to be coming from Enceladus. Equilibrium heating in possible past resonances likewise cannot explain prior resurfacing events. 相似文献
5.
It is now recognized that a number of neutral-plasma interaction processes are of great importance in the formation of the Io torus. One effect not yet considered in detail is the charge exchange between fast torus ions and the atmospheric neutrals producing fast neutrals energetic enough to escape from Io. Since near Io the plasma flow is reduced, the neutrals of charge exchange origin are not energetic enough to leave the Jovian system; these neutrals are therefore distributed over an extensive region as indicated by the sodium cloud. It is estimated here that the total neutral injection rate can reach 1027 s?1 if not more. New ions subsequently created in the distributed neutral atomic cloud as a result of charge exchange or electron impact ionization are picked up by the corotating magnetic field. The pick-up ions are hot with initial gyration speed near the corotation speed. The radial current driven by the pickup process cannot close in the torus but must be connected to the planetary ionosphere by field-aligned currents. These field-aligned currents will flow away from the equator at the outer edge of the neutral cloud and towards it at the inner edge. We find that the Jovian ionospheric photoelectrons alone cannot supply the current flowing away from the equator, and torus ions accelerated by a parallel electric field could be involved. The parallel potential drop is estimated to be several kV which is large enough to push the torus ions into the Jovian atmosphere. This loss could explain the sharp discontinuous change of flux tube content and ion temperature at L = 5.6 as well as the generation of auroral type hiss there. Finally we show that the inner torus should be denser at system III longitudes near 240° as a result of the enhanced secondary electron flux in this region. This effect may be related to the longitudinal brightness variation observed in the SII optical emissions. 相似文献
6.
Enceladus: Present internal structure and differentiation by early and long-term radiogenic heating 总被引：1，自引：0，他引：1
Pre-Cassini images of Saturn's small icy moon Enceladus provided the first indication that this satellite has undergone extensive resurfacing and tectonism. Data returned by the Cassini spacecraft have proven Enceladus to be one of the most geologically dynamic bodies in the Solar System. Given that the diameter of Enceladus is only about 500 km, this is a surprising discovery and has made Enceladus an object of much interest. Determining Enceladus' interior structure is key to understanding its current activity. Here we use the mean density of Enceladus (as determined by the Cassini mission to Saturn), Cassini observations of endogenic activity on Enceladus, and numerical simulations of Enceladus' thermal evolution to infer that this satellite is most likely a differentiated body with a large rock-metal core of radius about 150 to 170 km surrounded by a liquid water-ice shell. With a silicate mass fraction of 50% or more, long-term radiogenic heating alone might melt most of the ice in a homogeneous Enceladus after about 500 Myr assuming an initial accretion temperature of about 200 K, no subsolidus convection of the ice, and either a surface temperature higher than at present or a porous, insulating surface. Short-lived radioactivity, e.g., the decay of 26Al, would melt all of the ice and differentiate Enceladus within a few million years of accretion assuming formation of Enceladus at a propitious time prior to the decay of 26Al. Long-lived radioactivity facilitates tidal heating as a source of energy for differentiation by warming the ice in Enceladus so that tidal deformation can become effective. This could explain the difference between Enceladus and Mimas. Mimas, with only a small rock fraction, has experienced relatively little long-term radiogenic heating; it has remained cold and stiff and less susceptible to tidal heating despite its proximity to Saturn and larger eccentricity than Enceladus. It is shown that the shape of Enceladus is not that of a body in hydrostatic equilibrium at its present orbital location and rotation rate. The present shape could be an equilibrium shape corresponding to a time when Enceladus was closer to Saturn and spinning more rapidly, or more likely, to a time when Enceladus was spinning more rapidly at its present orbital location. A liquid water layer on Enceladus is a possible source for the plume in the south polar region assuming the survivability of such a layer to the present. These results could place Enceladus in a category similar to the large satellites of Jupiter, with the core having a rock-metal composition similar to Io, and with a deep overlying ice shell similar to Europa and Ganymede. Indeed, the moment of inertia factor of a differentiated Enceladus, C/MR2, could be as small as that of Ganymede, about 0.31. 相似文献
7.
To explain the formation of surface features on Europa, Enceladus, and other satellites, many authors have postulated the spatial localization of tidal heating within convective plumes. However, the concept that enhanced tidal heating can occur within a convective plume has not been rigorously tested. Most models of this phenomenon adopt a tidal heating with a temperature-dependence derived for an incompressible, homogeneous (zero-dimensional) Maxwell material, but it is unclear whether this formulation is relevant to the heterogeneous situation of a warm plume surrounded by cold ice. To determine whether concentrated dissipation can occur in convective plumes, we develop a two-dimensional model to compute the volumetric dissipation rate for an idealized, vertically oriented, isolated convective plume obeying a Maxwellian viscoelastic compressible rheology. We apply the model to the Europa and Enceladus ice shells, and we investigate the consequences for partial melting and resurfacing processes on these bodies. We find that the tidal heating is strongly temperature dependent in a convective ice plume and could produce elevated temperatures and local partial melting in the ice shells of Europa and Enceladus. Our calculation provides the first quantitative verification of the hypothesis by Sotin et al. [Sotin, C., Head, J.W., Tobie, G., 2002. Geophys. Res. Lett. 29. 74-1] and others that the tidal dissipation rate is a strong function of temperature inside a convective plume. On Europa, such localized heating could help allow the formation of domes and chaos terrains by convection. On Enceladus, localized tidal heating in a thermal plume could explain the concentrated activity at the south pole and its associated heat transport of 2-7 GW. 相似文献
8.
Recently, the Cassini spacecraft has detected ongoing geologic activity near the south pole of Saturn's moon Enceladus. In contrast, the satellite's north-polar region is heavily cratered and appears to have been geologically inactive for a long time. We propose that this hemispheric dichotomy is caused by interior dynamics with degree-one convection driving the south-polar activity. We investigate a number of core sizes and internal heating rates for which degree-one convection occurs. The numerical simulations imply that a core radius of less than 100±20 km and an energy input at a rate of 3.0 to 5.5 GW would be required for degree-one convection to prevail. This is within the range of the observed thermal power release near Enceladus' south pole. Provided that Enceladus is not fully differentiated, degree-one convection is found to be a viable mechanism to explain Enceladus' hemispheric dichotomy. 相似文献
9.
The thermal histories of two geologically active satellites of Saturn—Titan and Enceladus—are discussed. During the Cassini mission, it was found that there are both nitrogen-containing compounds—NH3 and N2-and CO2 and CH4 in the water plumes of Enceladus; at that, ammonia is the prevailing form. This may testify that during evolution, the material
of the satellite was warmed up to T ∼ 500–600 K, when NH3 (the form of nitrogen capable of being accreted) could only be partly converted into N2. Contrary to Enceladus, the temperature inside Titan probably reached values higher than 800 K or even higher than 1000 K,
since the process of the chemical dissociation of ammonia was completely finished on this satellite and its atmosphere contains
only molecular nitrogen. While the internal heating of Titan up to high temperatures can be explained by its large mass, the
heating source for Enceladus’ interior is far from evident. Such traditional heating sources as the energy of gravitational
differentiation and the radiogenic heating due to shortliving 26Al and 60Fe could not be effective. The first one is because of the small size of Enceladus (RE ≈ 250 km), and the inefficiency of the second one is caused by the fact that the satellite was formed not earlier than 8–10
Myr after the formation of calcium and aluminum-enriched inclusions in carbonaceous chondrites (CAI), i.e., after 26Al had completely decayed. In the present paper, we propose other heating mechanisms-the heat of long-living radioactive elements
and tidal heat, which could provide the observed chemical composition of the water plumes of Enceladus rather than only the
differentiation of its protomatter into the ironstone core and the ice mantle. 相似文献
10.
Thermal histories of the small icy Saturnian satellites Mimas, Tethys, Dione, Rhea, and Iapetus are constructed by assuming that they formed as homogeneous ice-silicate mixtures. The models include effects of radiogenic and accretional heating, conductive and subsolidus convective heat transfer, and lithospheric growth. Accretional heating is unlikely to have melted the water ice in the interiors of these bodies and solid state creep of the predominately ice material precludes melting by radiogenic heating. Mimas is so small that its thermal evolution is essentially purely conductive; at present it is a cold, nearly isothermal body. Any subsolidus convection or thermal activity in Mimas would have been confined to a brief period in its early history and would have been due to a warm formation. The four largest satellites are big enough and contain sufficient heat-producing silicates that solid state convection beneath a rigid lithosphere is inevitable independent of initial conditions. Dione and Rhea have convective interiors for most of their thermal histories, while Tethys and Iapetus have mainly conductive thermal histories with early periods of convective 0activity. The thermal histories of the five satellites for the last 4 by are independent of initial conditions; at present they have cold, conductive interiors. The model thermal histories are qualitatively consistent with the appearances of these satellites: Mimas has an ancient heavily cratered surface, Tethys and probably Iapetus have both heavily cratered and more lightly cratered areas, and Dione and Rhea have extensively modified surfaces. Because of their similar sizes and densities, Mimas and Enceladus are expected to have similar surfaces and thermal histories, but instead Enceladus has the most modified surface of all the small icy Saturnian satellites. Our results suggest a heat source for Enceladus, in addition to radiogenic and accretional heating; tidal dissipation is a possibility. Because the water ice in these bodies does not melt, resurfacing must be accomplished by the melting of a low-melting-temperature minor component such as ammonia hydrate. 相似文献
11.
The Cassini probe observed a young and smooth surface around the south pole of Enceladus, while around the north pole the surface was found to be relatively old and inactive (Porco, C.C. et al. [2006]. Science 311, 1393–1401). This heterogeneous surface implies that the ice thickness of Enceladus is not uniform between the north and south polar regions. Determining the thickness of the icy layer is important to confirm the existence of an internal ocean as well as to reveal the heating mechanism of Enceladus. We show that the measurement of radio waves induced by cosmic neutrinos can be an effective method to constrain the ice thickness of a localized area where conventional gravity or electromagnetic field measurements cannot be used. This method could be used to constrain the thickness of the icy layer on Enceladus even if the ice is a few tens of kilometers thick, measuring over a period of several years, which greatly exceeds the ability of radar sounding, and hence could be used in future orbiter missions. 相似文献
12.
《New Astronomy》2015
Despite the low elemental abundance of atomic deuterium in the interstellar medium (ISM), observational evidence suggests that several species, both in the gas phase and in ices, could be heavily fractionated. We explore various aspects of deuterium enrichment by constructing a chemical evolution model in both gaseous and granular phases. Depending on various physical parameters, gases and grains are allowed to interact with each other through the exchange of their chemical species. It is known that HCO+ and N2H+ are two abundant gas phase ions in the ISM and, their deuterium fractionation is generally used to predict the degree of ionization in the various regions of a molecular cloud. For a more accurate estimation, we consider the density profile of a collapsing cloud. The radial distributions of important interstellar molecules, along with their deuterated isotopomers, are presented. Quantum chemical simulations are computed to study the effects of isotopic substitution on the spectral properties of these interstellar species. We calculate the vibrational (harmonic) frequencies of the most important deuterated species (neutral and ions). The rotational and distortional constants of these molecules are also computed in order to predict the rotational transitions of these species. We compare vibrational (harmonic) and rotational transitions as computed by us with existing experimental and theoretical results. It is hope that our results will assist observers in detecting several hitherto unobserved deuterated species. 相似文献
13.
Voyager 2 images show parts of Enceladus' surface to be very smooth, lacking craters down to the resolution limit of 4 km. This absence of craters indicates geologically recent resurfacing, probably due to internal melting. However, calculations of current heating mechanisms, including radioactive decay and tidal heating due to Enceladus' resonance with Dione, yield heating rates too small to cause melting. The orbital mean motion of Janus (1980S1) is slightly less than twice that of Enceladus and, according to theoretical calculations, is currently decreasing as Janus' orbit evolves outward due to resonant torques from Saturn's rings. If Janus were ever locked into a stable 2:1 orbital commensurability with Enceladus, the resulting angular momentum transfer could have sufficiently enhanced the eccentricity of Enceladus' orbit for the ensuing tidal heating to have melted Enceladus' interior. The existence of a Laplace-like three-body resonance including Dione, although unlikely, would have increased heating. If Janus were indeed held in resonance with Enceladus until recently (107–108 years B.P.) when the lock was disrupted by an unspecified event (possibly a catastrophic collision which simultaneously created the coorbital pair, or by the influence of Dione) both the recent internal activity of Enceladus and the proximity of Janus to Saturn's rings may be explained. However, the predicted rapid time scale for ring evolution due to resonant torques from Saturn's inner moons remains a major problem. 相似文献
14.
N. Krupp E. Roussos P. Kollmann C. Paranicas D.G. Mitchell S.M. Krimigis A. Rymer G.H. Jones C.S. Arridge T.P. Armstrong K.K. Khurana 《Icarus》2012,218(1):433-447
The moon Enceladus, embedded in Saturn’s radiation belts, is the main internal source of neutral and charged particles in the Kronian magnetosphere. A plume of water ice molecules and dust released through geysers on the south polar region provides enough material to feed the E-ring and also the neutral torus of Saturn and the entire magnetosphere. In the time period 2005–2010 the Cassini spacecraft flew close by the moon 14 times, sometimes as low as 25 km above the surface and directly through the plume. For the very first time measurements of plasma and energetic particles inside the plume and its immediate vicinity could be obtained. In this work we summarize the results of energetic electron measurements in the energy range 27 keV to 21 MeV taken by the Low Energy Magnetospheric Measurement System (LEMMS), part of the Magnetospheric Imaging Instrument (MIMI) onboard Cassini in the vicinity of the moon in combination with measurements of the magnetometer instrument MAG and the Electron Spectrometer ELS of the plasma instrument CAPS onboard the spacecraft. Features in the data can be interpreted as that the spacecraft was connected to the plume material along field lines well before entering the high density region of the plume. Sharp absorption signatures as the result of losses of energetic electrons bouncing along those field lines, through the emitted gas and dust clouds, clearly depend on flyby geometry as well as on measured pitch angle/look direction of the instrument. We found that the depletion signatures during some of the flybys show “ramp-like” features where only a partial depletion has been observed further away from the moon followed by nearly full absorption of electrons closer in. We interpret this as partially/fully connected to the flux tube connecting the moon with Cassini. During at least two of the flybys (with some evidence of one additional encounter) MIMI/LEMMS data are consistent with the presence of dust in energetic electron data when Cassini flew directly through the south polar plume. In addition we found gradients in the magnetic field components which are frequently found to be associated with changes in the MIMI/LEMMS particles intensities. This indicates that complex electron drifts in the vicinity of Enceladus could form forbidden regions for electrons which may appear as intensity drop-outs. 相似文献
15.
Recent observations of the south pole of Saturn's moon Enceladus by the Cassini spacecraft have revealed an active world, powered by internal heat. In this paper, we propose that localized subsurface melting on Enceladus has produced an internal south polar sea. Evidence for this localized sea comes from the shape of Enceladus, which does not match a differentiated body at its current orbital position. We show that melting induced by the observed heat flow at the south pole produces a large enough pit to match the shape of Enceladus with a differentiated rock and ice interior. Numerical modeling of melting and ice flow shows that the sea produced beneath the south pole is stable against inflow of ductile ice from its surroundings for the duration of the heating. The shape modification due to melting also produces a negative degree-two gravity anomaly, which can reorient the spin axis of Enceladus in order to place the sea at the pole. 相似文献
16.
Quinn R. Passey 《Icarus》1983,53(1):105-120
High resolution Voyager II images of Enceladus reveal that some regions on its surface are highly cratered; the most heavily cratered surfaces probably date back to a period of heavy bombardment. The forms of many of the craters on Enceladus are similar to those of fresh lunar craters, but many of the craters are much shallower in depth, and the floors of some craters are bowed up. The flattering of craters and bowing up of the floors are indicative of viscous relaxation of the topography. Analysis of the forms of the flattened craters suggests that the viscosity at the top of the lithosphere, in the most heavily cratered regions, is between 1024 and 1025 P. The exact time scale for the collapse of the craters is not known, but probably was between 100 my and 4 gy. The flattened craters are located in distinct zones that are adjacent to zones, of similar age, where craters have not flattened. The zones where flattened craters occur possibly are regions in which the heat flow was (or is) higher than that in the adjacent terrains. Because the temperature at the top of the lithosphere of Enceladus would be less than or equal to that of Ganymede and Callisto, if it is covered by a thick regolith, and because the required viscosity on Enceladus is one to two orders of magnitude less than that for Ganymede and Callisto, it can be concluded that the lithospheric material on Enceladus is different from that of Ganymede and Callisto. Enceladus probably has a mixture of ammonia ice and water ice in the lithosphere, whereas the lithospheres of Ganymede and Callisto are composed primarily of water ice. 相似文献
17.
Tidal evolution of Mimas, Enceladus, and Dione 总被引：2，自引：0，他引：2
The tidal evolution through several resonances involving Mimas, Enceladus, and/or Dione is studied numerically with an averaged resonance model. We find that, in the Enceladus-Dione 2:1 e-Enceladus type resonance, Enceladus evolves chaotically in the future for some values of k2/Q. Past evolution of the system is marked by temporary capture into the Enceladus-Dione 4:2 ee′-mixed resonance. We find that the free libration of the Enceladus-Dione 2:1 e-Enceladus resonance angle of 1.5° can be explained by a recent passage of the system through a secondary resonance. In simulations with passage through the secondary resonance, the system enters the current Enceladus-Dione resonance close to tidal equilibrium and thus the equilibrium value of tidal heating of 1.1(18,000/QS) GW applies. We find that the current anomalously large eccentricity of Mimas can be explained by passage through several past resonances. In all cases, escape from the resonance occurs by unstable growth of the libration angle, sometimes with the help of a secondary resonance. Explanation of the current eccentricity of Mimas by evolution through these resonances implies that the Q of Saturn is below 100,000. Though the eccentricity of Enceladus can be excited to moderate values by capture in the Mimas-Enceladus 3:2 e-Enceladus resonance, the libration amplitude damps and the system does not escape. Thus past occupancy of this resonance and consequent tidal heating of Enceladus is excluded. The construction of a coherent history places constraints on the allowed values of k2/Q for the satellites. 相似文献
18.
We numerically model the formation and acceleration of a neutral gas shell as an ionization-shock front propagates in a spherical cloud by taking into account the photoionization and radiative heating of the gas, the spectral radiative transfer. We suggest and implement an approximation of the cooling function that allows calculations to be performed in a wide range of gas ionization fractions and temperatures. The total mass, average velocity, and thickness of the shell have been determined. The results are compared with approximate formulas known in the literature. Based on the parameters of the shell found, we estimate its acceleration, characteristic scales, and the growth times of unstable perturbations. We analyze the influence of the cloud particle density, cloud radius, stellar temperature, and radiation spectrum on the integrated characteristics of the neutral gas in the layer between the ionization and shock fronts. The distribution of matter in the shell and its thickness are shown to differ significantly from those used in approximate models. 相似文献
19.
Tidal dissipation has been suggested as the heat source for the south polar thermal anomaly on Enceladus. We find that under present-day conditions and assuming Maxwellian behavior, tidal dissipation is negligible in the silicate core. Dissipation may be significant in the ice shell if the shell is decoupled from the silicate core by a subsurface ocean. We have run a series of self-consistent convection and conduction models in 2D axisymmetric and 3D spherical geometry in which we include the spatially-variable tidal heat production. We find that in all cases, the shell removes more heat from the interior than can be produced in the core by radioactive decay, resulting in cooling of the interior and the freezing of any ocean. Under likely conditions, a 40-km thick ocean made of pure water would freeze solid on a ∼30 Ma timescale. An ocean containing other chemical components will have a lower freezing point, but even a water-ammonia eutectic composition will only prolong the freezing, not prevent it. If the eccentricity of Enceladus were higher (e?0.015) in the past, the increased dissipation in the ice shell may have been sufficient to maintain a liquid layer. We cannot therefore rule out the presence of a transient ocean, as a relic of an earlier era of greater heating. If the eccentricity is periodically pumped up, the ocean may have thickened and thinned on a similar timescale as the orbital evolution, provided the ocean never froze completely. We conclude that the current heat flux of Enceladus and any possible subsurface ocean is not in steady-state, and is the remnant of an epoch of higher eccentricity and tidal dissipation. 相似文献
20.
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