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1.
Douglas B. Nash 《Icarus》1983,54(3):511-523
The role of adsorbed SO2 on Io's surface particles in producing the observed spectral absorption band near 4 μm in Io's reflectance spectrum is explored. Calculations show that a modest 50% monolayer coating of adsorbed SO2 molecules on submicron grains of sulfur of alkali sulfide, assumed to make up Io's uppermost optical surface (“radialith”), will result in a ν1 + ν3 absorption band near 4 μm with depth ～30% below the adjacent continuum, consistent with the observed strength of the Io band. The precise wavelength position of the ν1 + ν3 band of SO2 in different phase states such as frost, ice, adsorbate, and gas are summarized from the experimental literature and compared with the available telescopic measurements of the Io band position. The results suggest that the 4-μm band in Io's full disk spectrum can best be explained by the presence on Io's surface of widespread SO2 in the form of adsorbate rather than ice or frost.  相似文献   

2.
An equation of heat transport in the Jovian magnetosphere is formulated and solved in the L range between 2 and 7. Sources of thermal energy include the heating associated with inward radial diffusion and a hypothetical heat supply originating from Io's dynamo action. The principal sink of the thermal energy is charge exchange in Io's hydrogen torus. In order to explain the density and temperature profile reported by Frank et al. (1976), the presence of the heat source at Io is essential and the density of the torus hydrogen has to be considerably lower than the value inferred from Lα observations by Carlson and Judge (1975). Radial diffusion represents the principal heating mechanism for plasma at very low L values.  相似文献   

3.
The available full-disk reflectance spectra of Io in the range 0.3 to 2.5 μm have been interpreted by comparison with new laboratory spectra of a wide variety of natural and synthetic mineral phases in order to determine a surface compositional model for Io that is consistent with Io's other known chemical and physical properties. Our results indicate that the dominant mineral phases are sulfates and free sulfur derived from them, which points toward a low temperature and initially water-rich surface assemblage. Our current preferred mineral phase mixture that best matches the Io data and is simultaneously most consistent with other constraints, consists of a fine-grained particulate mixture of free sulfur (55 vol%), dehydrated bloedite [Na2Mg(SO4)2·xH2O] (30 vol%) ferric sulfate [Fe2(SO4)3·xH2O] (15 vol%), and trace amounts of hematite [Fe2O3]. Other salts may be present, such as halite and sodium nitrate, as well as clay minerals. Such a model is consistent with a probable pre- and post-accretion thermal history of Io-forming material and Io's observed Na emission and other properties. These results further support the evaporite surface hypothesis of Fanale et al'; while not precluding the presence of certain silicate phases such as montmorillonite.The average surface of Io's leading hemisphere appears to contain less free sulfur and more salts and to be finer grained than that of the trailing hemisphere. Since Io is immersed in Jupiter's magnetosphere, irradiation damage effects from low-energy proton bombardment were studied. Irradiation damage of lattices is estimated to be a relatively minor but operative process on the surface of Io; irradiation darkening by sulfate reduction to free sulfur and by F-center production in salts may be partly responsible for the differences in albedo of leading and trailing hemispheres and equatorial and polar regions of Io, but slight regional differences in relative intrinsic phase concentration on the surface may likewise account for these global variations in albedo.Possible unusual surface properties predicted by this model include: posteclipse darkening in certain wavelenghts, limb brightening in certain wavelengths, and unusual surface electrical properties. Further refinement of Io's surface composition model and better understanding of surface irradiation effects will be possible when observational data in the range 0.20 to 0.30 μm are obtained and when improved spectra in the range 0.30 to 5.0 μm are obtained having increased spectral, spatial, and temporal resolution.  相似文献   

4.
Carl B. Pilcher 《Icarus》1979,37(3):559-574
A variety of processes have been examined to determine their impact on water loss from Io and the formation of an anhydrous surface. Thermal escape, photolysis, and gas-phase charged particle interactions are shown to be unimportant in this regard. Recent laboratory experiments have shown that charged-particle sputtering is likely to be an effective mechanism for the removal of water ice from Io's surface. Vaporization of ice by meteoroid impacts may also be significant. The overall sputtering rate appears to be sufficiently high that the formation of a substantial regolith due to meteoroid bombardment will be prevented. However, meteoroid bombardment is probably capable of maintaining a thin (? 500 μm overturned surface layer from which all free water has been removed by sputtering. Alternatively, a thick anhydrous surface layer may have formed on Io as the result of primordial heating. The survival of such a layer to the present implies the absence of subsequent water evolution onto the surface of the satellite.  相似文献   

5.
The effects of the equilibrium figure theory to within terms of the second order in a small parameter α on figure parameters and gravitational moments of the Galilean satellite Io have been considered. Integro-differential equations of the theory of figure to second order have been first solved numerically. Relations between the low-order coefficients of the gravitational field for satellites in hydrostatic equilibrium are generalized according to the second order theory. To show the effects of the second approximation, two three-layer trial models of Io are used. The considered models of the Io’s interiors differ by the size and density of the core, while having the same thickness and density of the crust, and the mantle density difference is only 20 kg/m3. The corrections of second order in smallness to the gravitational moments J2 and C22 decrease the third decimal digit of model gravitational moments by two units. As the effects of third and forth harmonics are determined mostly by outer layers of Io, to distinguish between model mantle density, the gravitational moments J4, C42 and C44 should be determined to accuracy with three or four decimal digits. The second order corrections mostly effect the semi-axis a, and less the semi-axes b and c.  相似文献   

6.
W. Macy  L. Trafton 《Icarus》1980,41(1):131-141
Models for the distribution of sodium in Io's vicinity and in a disk in Io's orbital plane, compared with observational data, support arguments (1) that Io is the source of the sodium, (2) that sodium is ejected from the inside hemisphere and most of the high velocity sodium which is observed is ejected from the leading inside quadrant, (3) that most of the sodium leads Io in Io's vicinity but follows Io at distances of more than 7Rj from Jupiter, (4) that a significant fraction of the sodium flux is ejected at large angles with respect to Io's orbital plane, (5) that the source velocity distribution has a pronounced high-velocity tail, and (6) that impact ionization by electrons is significant at large distances from Io.  相似文献   

7.
Ground-based optical observations of D1 and D2 line emissions from Jupiter’s sodium nebula, which extend over several hundreds of jovian radii, were carried out at Mt. Haleakala, Maui, Hawaii using a wide field filter imager from May 19 to June 21, 2007. During this observation, the east-west asymmetry of the nebula with respect to the Io’s orbital motion was clearly identified. Particularly, the D1+D2 brightness on the western side of Jupiter is strongly controlled by the Io phase angle. The following scenario was developed to explain this phenomenon as follows: First, more ionospheric ions like NaX+, which are thought to produce fast neutral sodium atoms due to a dissociative recombination process, are expected to exist in Io’s dayside hemisphere rather than in the nightside one. Second, it is expected that more NaX+ ionospheric ions are picked up by the jovian co-rotating magnetic field when Io’s leading hemisphere is illuminated by the Sun. Third, the sodium atom ejection rate varies with respect to Io’s orbital position as a result of the first two points. Model simulations were performed using this scenario. The model results were consistent with the observation results, suggesting that Io’s ionosphere is expected to be controlled by solar radiation just like Earth.  相似文献   

8.
The Io plasma torus, composed of mostly heavy ions of oxygen and sulfur, is sustained by an Iogenic mass loading rate of ∼1030 amu s−1 = 1.6 × 1028 SO2 s−1 or approximately 103 kg s−1(A.L. Broadfoot et al., 1979, Science 204, 979-982). We argue on the basis of available power sources, reanalysis of F. Bagenal (1997, Geophys. Res. Lett. 24, 2111-2114), HST UV remote sensing, and detailed model calculations that at most 20% of this mass leaves Io in the form of ions, i.e., ≤3 × 1027 × (ne,0/3600 cm−3) ions s−1, where ne,0 is the average torus electron density. For the Galileo spacecraft Io pass in December 1995, the ion mass loading rate was ≤3 × 1027 ions s−1, whereas for the Voyager epoch with lower ne,0 (=2000 cm−3), this rate would be ≤1.7 × 1027 ions s−1, consistent with the D.E. Shemansky (1980, Astrophys. J. 242, 1266-1277) mass loading limit of ≤1 × 1027 ions s−1. We investigate the processes that control Io’s large scale electrodynamic interaction and find that the elastic collision rate exceeds the ionization/pickup rate by at least a factor of 5 for all atmospheric column densities considered (1016-1021 m−2) and by a factor of ∼100 for the most realistic column density. Consequently, elastic collisions are mostly responsible for Io’s high conductances and thus generate Io’s large scale electrodynamic interaction such as the generation of Io’s electric current system and the slowing of the plasma flow. The electrodynamic part of Io’s interaction is thus best described as an ionosphere-like interaction rather than a comet-like interaction. An analytic expression for total electron impact rates is derived for Io’s atmosphere, which is independent of any particular model for the 3D interaction of torus electrons with its atmosphere.  相似文献   

9.
We obtained time-resolved, near-infrared spectra of Io during the 60-90 min following its reappearance from eclipse by Jupiter on five occasions in 2004. The purpose was to search for spectral changes, particularly in the well-known SO2 frost absorption bands, that would indicate surface-atmosphere exchange of gaseous SO2 induced by temperature changes during eclipse. These observations were a follow-on to eclipse spectroscopy observations in which Bellucci et al. [Bellucci et al., 2004. Icarus 172, 141-148] reported significant changes in the strengths of two strong SO2 bands in data acquired with the VIMS instrument aboard the Cassini spacecraft. One of the bands (4.07 μm [ν1 + ν3]) observed by Bellucci et al. is visible from ground-based observatories and is included in our data. We detected no changes in Io’s spectrum at any of the five observed events during the approximately 60-90 min during which spectra were obtained following Io’s emergence from Jupiter’s shadow. The areas of the three strongest SO2 bands in the region 3.5-4.15 μm were measured for each spectrum; the variation of the band areas with time does not exceed that which can be explained by the Io’s few degrees of axial rotation during the intervals of observation, and in no case does the change in band strength approach that seen in the Cassini VIMS data. Our data are of sufficient quality and resolution to show the weak 2.198 μm (4549.6 cm−1) 4ν1 band of SO2 frost on Io for what we believe is the first time. At one of the events (June 22, 2004), we began the acquisition of spectra ∼6 min before Io reappeared from Jupiter’s shadow, during which time it was detected through its own thermal emission. No SO2 bands were superimposed on the purely thermal spectrum on this occasion, suggesting that the upper limit to condensed SO2 in the vertical column above Io’s surface was ∼4 × 10−5 g cm−2.  相似文献   

10.
Radiation damage and luminescence, caused by magnetospheric charged particles, have been suggested by several authors as mechanisms for explaining some of the peculiar spectral/albedo features of Io. We have pursued this possibility by measuring the uv-visual spectral reflectance and luminescent efficiency of several proposed Io surface constituents during 2 to 10-keV proton irradiation at room temperature and at low temperature (120 < T < 140°K). The spectral reflectance of NaCl and KCl during proton irradiation exhibits the well-known F-center absorption bands at 4580 and 5560 Å. Na2SO4 shows a generalized darkening which increases toward longer wavelengths. NaNO3 shows a spectral reflectance change indicative of the partial alteration of NaNo3 to NaNo2. NaNO2 shows no change. The luminescent efficiencies of NaCl and KCl are ～10?4 at 300°K and increase by one-half order of magnitude at ～130°K. The efficiencies of K2CO3, Na2CO3, Na2SO4, and NaNO3 are 10?4, 10?4, 10?5 and 10?6, respectively, at 300°K and they all decrease by one-half order of magnitude at ～130°K. These results indicate that magnetospheric proton irradiation of Io could cause spectral features in its observed ultraviolet and visible reflection spectrum if salts such as those studied here are present on its surface. However, because the magnitude of these spectral effects is dependent on competing factors such as surface temperature, incident particle energy flux, solar bleaching effects, and trace element abundance, we are unable at this time to make a quantitative estimate of the strength of these spectral effects on Io. The luminescent efficiencies of pure samples that we have studied in the laboratory suggest that charged-particle induced luminescence from Io's surface might be observable by a spacecraft such as Voyager when viewing Io's dark side.  相似文献   

11.
Io's neutral sodium emission cloud was monitored during the period of Voyager 1 encounter from two independent ground-based sites. Observations from Table Mountain Observatory verified the continued existence of the “near-Io cloud” (d < 1.5 × 105 km, for 4πI > 1 kR; R denotes Rayleigh) while those from Wise Observatory showed a deficiency in the weaker emission at greater distances from Io. The sodium cloud has been monitored from both observatories for several years. These and other observations demonstrate that the behavior of the cloud is complex since it undergoes a variety of changes, both systematic and secular, which can have both time and spatial dependencies. The cloud also displays some characteristics of stability. Table Mountain images and high-dispersion spectra (resolution ～0.2 A?) indicate that the basic shape and intensity of the “near cloud” have remained relatively constant at least since imaging observations began in 1976. Wise Observatory low-dispersion spectra (resolution ～1 A?) which have been obtained since 1974 demonstrate substantial variability of the size and intensity of the “far cloud” (d ? 1.5 × 105 km) on a time scale of months or less. Corresponding changes in the state of the plasma associated with the Io torus are suggested, with the period of Voyager 1 encounter represented as a time of unusually high plasma temperature and/or density. Dynamic models of the sodium cloud employing Voyager 1 plasma data provide a reasonable fit to the Table Mountain encounter images. The modeling assumptions of anisotropic ejection of neutral sodium atoms from the leading, inner hemisphere of Io with a velocity distribution characteristic of sputtering adequately explain the overall intensity distribution of the “near cloud”. During the Voyager 1 encounter period there appeared a region of enhanced intensity projecting outward from Io's orbit and inclined to the orbital plane. This region is clearly distinguished from the sodium emission normally aligned with the plane of Io's orbit. The process responsible for this phenomenon is not yet understood. Similar but less pronounced features are also present in several Table Mountain images obtained over the past few years.  相似文献   

12.
Using Voyager results, we have made crude estimates of the rate at which Io loses volatiles by a variety of processes to the surrounding magnetosphere for both the current SO2-dominated atmosphere as well as hypothetical paleoatmospheres in which other gases, such as N2, may have been the dominant constituent. Loss rates are strongly influenced by the surface pressure on the night side, the relationship between the exobase and the Jovian magnetospheric boundary, the exospheric temperature, and the peak altitudes reached by volcanic plumes. Several mechanisms make significant contributions to the prodigious rate at which Io is currently losing volatiles. These include: interaction of the magnetospheric plasma with volcanic plume particles and the background atmosphere; sputtering of ices on the surface, if the nightside atmospheric pressure is low enough; and Jeans' escape of O, a dissociation product of SO2 gas. For paleoatmospheres, only the first two of these mechanisms would have been effective. However, they are capable of eliminating large amounts of N2 and other volatiles from Io over the satellite's lifetime. Io could have also lost large amounts of water over its lifetime due to the extensive recycling of water between its upper and lower crust, with the partial dissociation of water vapor in silicate magma chambers initiating this loss process. Significant amounts of water may also have been lost as a result of the interaction of the magnetospheric plasma with water ice particles in volcanic plumes. Once an SO2-dominated atmosphere becomes established, much water may have also been lost through the sputtering of surface water ice.  相似文献   

13.
We have obtained reflectivity spectra of the trailing and leading sides of all four Galilean satellites with circular variable filter wheel spectrometers operating in the 0.7- to 5.5-μm spectral interval. These observations were obtained at an altitude of 41,000 ft from the Kuiper Airborne Observatory. Features seen in these data include a 2.9-μm band present in the spectra of both sides of Callisto; the well-known 1.5-μm and 2.0-μm combination bands and the previously more poorly defined 3.1-μm fundamental of water ice observed in the spectra of both sides of Europa and Ganymede; and features centered at 1.35 ± 0.1, 2.55 ± 0.1, and 4.05 ± 0.05 μm noted in the spectra of both sides of Io. In an effort to interpret these data, we have compared them with laboratory spectra as well as synthetic spectra constructed with a simple multiple-scattering theory. We attribute the 2.9-μm feature of Callisto's spectra primarily to bound water, with the product of fractional abundance of bound water and mean grain radius in micrometers equaling approximately 3.5 × 10?1 for both sides of the satellite. The fractional amounts of water ice cover on the trailing side of Ganymede, its leading side, and the leading side of Europa were found to be 50 ± 15, 65 ± 15, and 85% or greater, respectively. The bare ground areas on Ganymede have reflectivity properties in the 0.7- to 2.5-μm spectral region comparable to those of Callisto's surface and also have significant quantities of bound water, as does Callisto. Interpretation of the spectrum for the trailing side of Europa is complicated by magnetospheric particle bombardment which causes a perceptible broadening of strong bands, but the ice cover on this side is probably comparable to that on the leading side. These irradiation effects may be responsible for much of the difference in the visual geometric albedos of the two sides of Europa. Minor, but significant, amounts of ferrous-bearing material (either ferrous salts or alkali feldspars but not olivines or pyroxenes) account for the 1.35-μm feature of Io. The two longer wavelength bands are most likely attributable to nitrate salts. Ferrous salts and nitrates can jointly also account for much of the spectral variation in Io's visible reflectivity, thereby eliminating the need to postulate large quantities of sulfur. The absence of noticeable features near 3-μm wavelength in Io's spectra leads to upper bounds of 10% on the fractional cover of water and ammonia ice and 10?3 on the relative abundance of bound water and hydroxylated material on Io. The two sides of Io have similar compositions. We suggest that the systematic increase in fractional water ice cover from Callisto to Ganymede to Europa is bought about by variations in efficiencies of recoating the satellite's surface by interior water brought to the surface, and by the deposition of extrinsic dust. The most important component of the latter is debris, derived from the outer irregular satellites of Jupiter, which impacts the Galilean satellites at relatively low velocities. Europa has the largest water ice cover because its crust is thinnest and thus the frequency of water recoating is the greatest, and because it is farthest from the sources of low-velocity dust. While models which depict Io's surface as consisting primarily of very fine-grained ice are no longer viable, we are unable to definitively distinguish between the salt assemblage and alkali feldspar models. The salt model can better account for Io's reflectivity spectrum from 0.3 to 5 μm, but the absence of appreciable quantities of bound water and hydroxylated material may not be readily understood within the context of that model.  相似文献   

14.
Because of relative motion between the innermost Galilean satellite Io and Jupiter's ionosphere, a current is drawn from the ionosphere that can be a source of both deposition on, and sputtering from, the surface of Io. We show that the ions in this current strike lo in a localized region in the quadrant bounded by a line connecting lo and Jupiter and a tangent line extended in the direction of Io's orbital motion. If these ions are the principal source of sodium that is sputtered from Io, then this current provides a simple explanation of the observation of a localized area from which sodium ions escape from Io. The geometry of this current may also affect the optical surface of Io. We suggest several experimental tests that can determine the compatibility of this hypothesis with the directly observable properties of Io's surface.  相似文献   

15.
Strong evidence that Io's sodium emission is due to resonant scattering is given by our observations which show a monotonic increase of emission intensity with residual solar intensity. In addition we detected no emission during three eclipse observations of Io. We propose a resonant scattering model with two spacial components comprising an optically thick atmosphere extending 103 km above Io's surface surrounded by an optically thin cloud which forms a partial torus around Jupiter. In this model a flux of 107 cm?2 sec?1 sodium atoms are sputtered from Io's surface by heavy energetic ions which are accelerated in a plasma sheath around Io. The atoms sputtered from the surface collide with atoms in Io's atmosphere so the equipartition of kinetic energy is established. The total sodium abundance is about 3 × 1013 cm?2. During Io's day, sodium and other atmospheric constituents are ionized, giving rise to the ionosphere observed by Pioneer 10. Atoms escape by means of Jeans escape from the critical level, which is at the top of the atmosphere and the base of the cloud. We have observed sodium emission 6arcsec (6 Io diameters) above and below Io's orbital plane and 23arcsec toward Jupiter in Io's orbital plane. No emission was detected at maximum elongation 180° from Io. We interpret these results to mean that atoms escaping from Io form a partial torus whose thickness is about 12 arcsec and whose length is at least one-fifth of Io's orbital circumference.  相似文献   

16.
We have undertaken mapping and spectroscopy of a broad range of type I post-Main-Sequence nebulae in COJ=1→0,J=2→1, andJ=3→2, using the 12 m antenna at Kitt Peak, and the 45 m facility of the Nobeyama Radio Observatory. As a consequence, we find COJ=2→1 emission associated with NGC 3132 and NGC 6445, determine the location of COJ=1→0 emission in the nucleus of NGC 6302, and obtain (for the first time) COJ=3→2 spectroscopy for a substantial cross-section of type I sources. LVG analysis of the results suggests densitiesn(H2) ～ 104 cm?3, and velocity gradients dv/dr ～ 2×102 in both NGC 7027 and CRL 618, commensurate with uniform expansion of a constant velocity outflow, whilst for the case of NGC 2346 these values probably exceedn(H2) ～ 4.0×105 cm?3. dv/dr ～ 2.6×103 km s?1 andT k ～102 K, implying appreciable compression (and shock heating?) of the CO excitation zone. Hi masses extend over a typical range 0.01<M(Hi)/M ⊙<1, whilst corresponding estimates of the progenitor mass imply 0.7<M prog/M ⊙<2.3; values significantly in excess of those pertinent for normal PN, although somewhat at the lower end of the type I mass range. COJ=3→2 profiles for CRL 2688 confirm the presence of an extended plateau with width Δv～85 km s?1, whilst modestJ=3→2 enhancement is also observed for the high-velocity components in NGC 7027. TheJ=3→2 spectrum for NGC 2346 appears to mimic lower-frequency results reasonably closely, confirming the presence of a double-peaked structure towards the core, and predominantly unitary profiles to the north and south, whilst there is also evidence to suggest appreciableJ=3→2 asymmetry in CRL 618 compared to lower-frequency measures. The status of an extended cloud near HB 5 remains uncertain, although this clearly represents a remarkably complex region with velocity span ΔV～50 km s?1. Our presentJ=3→2 results appear to track lower frequency measures extremely closely, implying local densitiesn(H2)>3×103 cm?3—although temperatures close to theV lsr of HB 5 are relatively weak, and of orderT MB (J=3→2)≤0.9 K. Finally, as a result of both this, and previous investigations we find that of type I sources so far observed in CO, some ～42% appear to possess detectable levels of emissionT r * >0.1 K. Similarly, in cross-correlating this data with other results, we note a closely linear relation betweenJ=2→1 antenna temperaturesT MB, and the surface brightness of H2 S(1) quadrupole emissionS(H2)—a trend which appears also to be reflected betweenS(H2) and corresponding parameters for [Oi], [Oii], [Ni], [Nii], and [Sii]. Such relations almost certainly arise from comparable secular variations in line intensities, although the CO, H2, and optical emission components are likely to derive from disparate line excitation zones. As a consequence, it is clear that whilst H2 S(1) emission is probably enhanced as a result of local shock activity, the evidence for post-shock excitation of the CO and optical forbidden lines is at best marginal. Similarly, although it seems likely that CO emission derives from circum-nebular Hi shells with kinetic temperatureT k ～ 30 K or greater, the predominant fraction of low-excitation emission arises from a mix of charge exchange reactions, nebular stratification and, probably most importantly, the influence of UV shadow zones and associated neutral inclusions.  相似文献   

17.
The temperatures of prolate and oblate spheroidal dust grains in the envelopes of stars of various spectral types are calculated. Homogeneous particles with aspect ratios a/b≤10 composed of amorphous carbon, iron, dirty ice, various silicates, and other materials are considered. The temperatures of spherical and spheroidal particles were found to vary similarly with particle size, distance to the star, and stellar temperature. The temperature ratio T d(spheroid)/T d(sphere) depends most strongly on the grain chemical composition and shape. Spheroidal grains are generally colder than spherical particles of the same volume; only iron spheroids can be slightly hotter than iron spheres. At a/b≈2, the temperature differences do not exceed 10%. If a/b≥4, the temperatures can differ by 30–40%. For a fixed dust mass in the medium, the fluxes at wavelengths λ≥100 are higher if the grains are nonspherical, which gives overestimated dust masses from millimeter observations. The effect of grain shape should also be taken into account when modeling Galactic-dust emission properties, which are calculated when searching for fluctuations of the cosmic microwave background radiation in its Wien wing.  相似文献   

18.
Observations of the 4-μm SO2 band on Jupiter's satellite Io and laboratory measurements of SO2 frost are presented. The observations confirm the existence of a large longitudinal variation in band strength but show no evidence of temporal changes. Comparison of the band position and shape in Io's spectrum with those in the laboratory frost's suggests that the bulk of the absorption on Io is due to frost, not adsorbed gas. The derived SO2 coverage is large enough to require that SO2 be present in most terrain types on Io and not just in the white plains unit. To reconcile the infrared observations that indicate large amounts of SO2 with the ultraviolet observations of Voyager and IUE that show little, the SO2 must be mixed intimately with the sulfur (or other material) so that at each wavelength the darker component dominates the spectrum.  相似文献   

19.
We consider the cooling of neutron stars with superfluid cores composed of neutrons, protons, and electrons (for singlet proton pairing and triplet neutron pairing). The emphasis is on triplet neutron pairing with the component of the total moment of neutron pairs along the quantization axis |m J | = 2. This case stands out in that it leads to power-law rather than exponential suppression of the main neutrino processes by neutron superfluidity. For the chosen critical neutron temperatures T cn, the cooling with |m J | = 2 proceeds either almost in the same way as the commonly considered cooling with m J =0 or appreciably faster. The cooling with variable (over the core) critical temperatures T cn(ρ) and T cp(ρ) can generally be described by the cooling with some effective constant temperatures T cn and T cp. The hypothesis of strong neutron superfluidity with |m J | = 2 is in conflict with the observational data on the thermal radiation from isolated neutron stars; the hypothesis of weak neutron superfluidity of any type is consistent with the observations.  相似文献   

20.
One of the intrinsic properties of particulate sulfur allotropes is a change in UV-visible reflectivity with temperature change of the material. The surface of Io experiences temperature changes during eclipse which are sufficient to cause a detectable change in the spectral reflectivity of sulfur; thus, if the surface of Io is composed primarily of sulfur allotropes, a change in reflectivity at certain wavelengths should be observable shortly after eclipse reappearance. We observed four eclipse reappearances during July and August of 1983 and saw no posteclipse brightening effects in filter bands selected for sensitivity to color changes in sulfur. Our model of the brightness change for S8 (“yellow” sulfur) implies that this material covers less than 50% of Io's surface. Negative posteclipse brightening observations were also obtained with a filter chosen for the high contrast between SO2 frost and the average albedo of the surface of Io at that wavelength. We conclude that no significant condensation of optically thick SO2 occurred on the surface of Io during these eclipses.  相似文献   

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