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1.
Interference filter photometry was taken of Comet Encke on June 14, 1974 (1.07 AU heliocentric distance, postperihelion) at the CTIO (Cerro Tololo Interamerican Observatory) 150-cm reflector. Production rates were calculated of 4.1 × 1023 mol sec?1 of CN, 5.3 × 1023 mol sec?1 of C3, and 4.3 × 1024 mol sec?1 of C2. These are about three times smaller than at comparable heliocentric distance preperihelion, assuming a value of 100 for the ratio H2O/ (C2 + C3 + CN). An upper limit was placed on the production of nonvolatiles at about one-third that of volatiles in mass by assuming a bulk density of 1 g cm?3, a particle geometric albedo of 0.1, and a phase function of 0.2. 相似文献
2.
The motion of fragments following a catastrophic destruction by either a normal or an oblique impact at 2.5–2.9 km sec?1 into cubic and spherical basalt targets was studied with a high-speed framing camera. Velocities at the antipodes of the targets vary as (E/M)0.75 (E = impact energy; M = target mass) and are lower than 200 m sec?1 at E/M ? 109 ergs g?1. Excluding fine-grained particles from the impact site, 70 to 80% by mass fraction of the fragments have velocities lower than twice the antipodal velocity. Comminution and ejection energies wasted in this mass fraction were a few percent of the impact energy at E/M ? 5 × 107 ergs g?1. During a catastrophic impact into asteroids some of the fragmented bodies can be reconcentrated by mutual gravitation. 相似文献
3.
Two monochromatic pictures of the Comet Kohoutek (1973f) were taken on January 15, 1974 in the resonance light (A2Σ ? X2 ∏) of the radical OH with a photographic telescope placed on board the NASA 990 Convair airplane. From an intensity profile we derive the production rate of OH radicals QOH = 4 xsx 1028 moleculesec ?1sr?1 at 0.6 AU and the lifetime of the OH radical which is τOH = 4.5 × 104 sec at 0.6 AU. This short lifetime (very similar to the lifetime of H2O) combined with the high total production rate of gas in comets can explain the observed velocity of 8km sec?1 for the H-atoms: The H-atoms produced by photodissociation of H2O are thermalized at short distancesfrom the nucleus; the H-atoms produced by photodissociation of OH have a velocity of ?8km sec?1 and can reach the outer part of the hydrogen envelope. 相似文献
4.
Material from the Galilean satellites of Jupiter ejected by energetic particles in the Jovian magnetosphere may provide large sources of oxygen to the parent planet. Formation of a CO molecule is the ultimate fate of an oxygen atom in the upper Jovian atmosphere. This high altitude source of CO supports Beer and Taylor's (1978, Astrophys. J.221) observations and analysis, provided that the globally averaged O atom input flux is ～107 cm?2 sec?1 and the eddy diffusion coefficient at the tropopause is ～103 cm2 sec?1. Implications for the possible presence of other atoms and molecules derived from the satellites are discussed. 相似文献
5.
The rates of photodissociation of the OH and OD molecules from absorption of solar radiation in he X2Π-A2Σ+ electronic transition are calculated to lie between 3.5 and 6.7 × 10?6 sec?1 for OH for heliocentric velocities between -60 and +60 km sec?1 and to be about 4.7 × 10?7 sec?1 for OD at 1 AU from the Sun. The corresponding lifetimes, which are upper bounds to the actual lifetimes, are generally consistent with the observational cometary data. 相似文献
6.
Some relationships between solar X-ray bursts and SPA's produced on VLF propagation in the lower ionosphere 总被引：1，自引：0，他引：1
This paper discusses SPA's measured at long VLF propagation paths in the lower ionosphere and their association with solar X-ray bursts observed by USNRL satellites in the 0–3 Å, 0–8 Å and 8–20 Å bands. Excellent correlations were found between the SPA importances (in degrees per Mm) and the logarithm of the X-ray burst peak intensities. A hardening of the X-ray burst spectra is evident for increasing importance of SPA's; the threshold energy required for the occurrence of such anomalies was estimated, it is 4.3×10?5 ergs cm?2 sec?1 in the main ionizing band of 0–3 Å. It was also possible to derive the effective recombination coefficient at the normal D-region height of 70 km, this beingα r≈6×10?6 cm3 sec?1; furthermore ion production rates were estimated during SPA's at heights below the reference level. 相似文献
7.
V.A. Krasnopolsky 《Icarus》1979,37(1):182-189
Observations and model calculations of water vapor diffusion suggest that about half the amount of water vapor is distributed with constant mixing ratio in the Martian atmosphere, the other half is the excess water vapor in the lower troposphere. During 24 hr the total content of water vapor may vary by a factor of two. The eddy diffusion coefficient providing agreement between calculations and observations is K = (3–10) × 106 cm2 sec?1 in the troposphere. An analytical expression is derived for condensate density in the stratosphere in terms of the temperature profile, the particle radius r, and K. The calculations agree with the Mars 5 measurements for r = 1.5 μm, condensate density 5 × 10?12 g/cm3 in the layer maximum at 30 to 35 km, condensate column density 7 × 10?6 cm?2, K = (1?3) × 106 cm2 sec?1, and the temperature profile T = 185 ? 0.05z ? 0.01z2 at 20 to 40 km. Condensation conditions yield a temperature of 160°K at 60 km in the evening; the scale height for scattered radiation yields T = 110°k at 80 to 90 km. The Mars model atmosphere has been developed up to 125 km. 相似文献
8.
The UCSD X-ray telescope on OSO-3 scanned Jupiter for 33 days during February and March 1968. We have searched the data for a steady Jovian flux, and for a burst component at times of decametric radio bursts. Neither component was detected at a sensitivity of ～0.1 photon (cm2sec)?1 for hv > 7.7 keV. At 4.4AU, the 3σ upper limits correspond to X-ray luminosities of 7.4 × 1019 ergs sec?1 for the steady component, and 2 × 1020 ergs sec?1 for the burst component. The observations occurred during a period of high solar activity, during which three sudden-commencement magnetic storms were observed at Earth. We compare the upper limits with several different calculations of the expected flux levels, and conclude that major improvements in X-ray detection techniques will be required before Jovian X rays can be detected with near-Earth observations. 相似文献
9.
Experimental data describing the effect of the South Atlantic anomaly on E? 280 keV electron flux at L = 2 and high B values, are compared to the numerical solution of a pitch-angle diffusion equation with a varying loss cone. The diffusion coefficient needed to explain replenishment of the electrons lost over the anomaly is found to be 3.2 × 10?2 sec?1 Calculation of the diffusion coefficient due to cyclotron resonant interaction with VLF electro-magnetic waves leads to the conclusion that the observed wave spectral density can yield the needed diffusion coefficient. 相似文献
10.
We find that faint sodium emission originating in the middle Jupiter magnetosphere has two distinct kinematical components. The “normal” signature of atoms on bound orbits with large apojoves seems always to be present, and we suggest these atoms are an extension of the bright, near-Io sodium cloud. The “fast” signature, with speeds up to at least 100 km sec?1, is seen only occasionally, and we suggest it is due to an interaction of the near-Io sodium cloud with the corotating, heavy-ion plasma. Both elastic and charge-exchange collisions seem consistent with the observed kinematical and temporal signatures. Elastic collisions seem marginally more capable of producing the high observed sodium atom speeds. We predict observable occurences of the fast component in the hours following passage of the Io sodium cloud through the plasma centrifugal symmetry surface if Io is at a favorable orbital longitude. Between 10 and 20 RJ we find an atomic sodium density ～10?2 cm?3. If the photoionization lifetime applies, an Io source of at least 1026 sodium atoms sec? is required to maintain this remote sodium population. 相似文献
11.
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
12.
A model is presented for the photochemistry of PH3 in the upper troposphere and lower stratosphere of Saturn that includes the effects of coupling with NH3 and hydrocarbon photochemistry, specifically the C2H2 catalyzed photodissociation of CH4. PH3 is rapidly depleted with altitude (scale height ～35 km) in the upper troposphere when K～104cm2sec?1; an upper limit for K at the tropopause is estimated at ～105cm2sec?1. If there is no gas phase P2H4 because of sublimation, P2 and P4 formation is unlikely unless the rate of the spin-forbidden recombination reaction PH + H2 + M → PH3 + M is exceedingly slow. An upper limit P4 column density of ～2×1015cm?2 is estimated in the limit of no recombination. If sublimation does not remove all gas phase P2H4, P2 and P4 may be produced in potentially larger quantities, although they would be restricted almost entirely to the lowest levels of our model, where T?100°K. Potentially observable amounts of the organophosphorus compounds CH3P2H2 and HCP are predicted, with column densities of >1017 cm?2 and production rates of ～2×108cm?2sec?1. The possible importance of electronically excited states of PHx and additional PH3/hydrocarbon photochemical coupling paths are also considered. 相似文献
13.
The pattern of radial growth of an extended spoke recorded in the Voyager 2 low-resolution ring movie has been examined. This feature is atypical in that it orbits Saturn at the corotational rate for 1½hr after the onset of its formation and then undergoes a 40-min acceleration to sustained Keplerian velocities. The spoke exhibits two modes of radial growth. The first is a diffusion of material radially inward (at a rate of 101 ± 4m sec?1) and outward (at a rate of 40 ± 5m sec?1) that occurs throughout the feature's life. The second mode is a short-lived, rapid outward propagation of material (at a rate of 730 ± 70m sec?1) that occurs for approximately the first 50 min of the spoke's Keplerian dynamical phase. This rapid propagation, presumably driven by Lorentz forces acting on the negatively charged spoke particulates, allows charge-to-mass ratios for these particulates to be calculated at the onset of the propagation (?60 ± 1C kg?1), the termination of the propagation (?22 ± 2C kg?1), and the final dissipation of the spoke (?1.5 ± 0.2C kg?1). The value at the termination of the rapid propagation can be taken as an upper limit on the particulate charge-to-mass ratios of spokes which exhibit Keplerian velocities throughout their lifetimes. A correlation between the dynamical phases and the radial growth modes of the atypical spoke is observed, one that seems consistent with the plasma cloud model of spoke formation and evolution proposed by C. K. Goertz and G. Morfill (1983, Icarus53, 219–229), taken in the limit of high charge density. 相似文献
14.
We have constructed a model of the physical processes controlling Titan's clouds. Our model produces clouds that qualitatively match the present observational constraints in a wide variety of model atmospheres, including those with low atmospheric pressures (25 mbar) and high atmospheric pressures. We find the following: (1) high atmospheric temperatures (160°K) are important so that there is a large scale height in the first few optical depths of cloud; (2) the aerosol mass production occurs at very low aerosol optical depth so that the cloud particles do not directly affect the photochemistry producing them; (3) the production rate of aerosol mass by chemical processes is probably greater than 3.5 × 10?14 g cm?2 sec?1; (4) and the eddy diffusion coefficient is less than 5 × 106 cm2 sec?1 except perhaps in the top optical depth of the cloud. Our model is not extremely sensitive to particle shape, but it is sensitive to particle density. Higher particle densities require larger aerosol mass production rates to produce satisfactory clouds. Particle densities of unity require a mass production rate on the order of 3.5 × 10?13 g cm?2 sec?1. We also show that an increase in mass input causes a decrease in the mean particle size, as required by J. B. Pollack et al. (1980, Geophys. Res. Lett. 7, 829–832), to explain the observed correlation between the solar cycle and Titan's albedo; that coagulation need not be extremely inefficient in order to obtain realistic clouds as proposed by M. Podolak and E. Podolak (1980, Icarus43, 73–83); that coagulation could be inefficient due to photoelectric charging of the particles; and, that the lifetime of particles near the altitude of unit optical depth is a few months, as required to explain the temporal variability observed by S. T. Suess and G. W. Lockwood and D. P. Cruikshank and J. S. Morgan (1979, Bull. Amer. Astron. Soc.11, 564). Although Titan's aerosols are ottically thick in the vertical direction, the atmosphere is so extended that the horizontal visibility is greater than that found anywhere at Earth's surface. 相似文献
15.
The first results of a comprehensive computer analysis of over 300 front film and grid coincidence events is presented using statistical tests on the observed data. The short term time dependence of the observed flux is entirely commensurate with a random Poisson distribution and any possible contributions from discrete “cometary showers” must certainly be of relatively minor significance compared to the sporadic background for mass > 10?13 g. Periodic seasonal variations of ～ 20 per cent of the average rate are observed common to Pioneers 8 and 9. These variations could reflect on the cometary nature of the source or alternatively indicate the presence of an interstellar component. The mass spectrum of the flux in the range 10?11?10?13 g indicates an increasing flux of particles to the lowest limits of mass detected, with a derived flux of Φ = 1·4 × 10?12m?0·68 (g) m?2 sec?1(2π ster.)?1. 相似文献
16.
Calculations of the steady-state photoelectron energy and angular distribution in the altitude region between 120 and 1000 km are presented. The distribution is found to be isotropic at all altitudes below 250 km, while above this altitude anisotropies in both pitch angle and energy are found. The isotropy found in the angular distribution below 250 km implies that photoelectron transport below 250 km is insignificant, while the angular anisotropy found above this altitude implies a net photoelectron current in the upward direction. The energy anisotropy above 500 km arises from the selective backscattering of the low energy photoelectron population of the upward flux component by Coulomb collisions with the ambient ions. The total photoelectron flux attains its maximum value between about 40 and 70 km above the altitude at which the photoelectron production rate is maximum. The displacement of the maximum of the equilibrium flux is attributed to an increasing (with altitude) photoelectron lifetime. Photoelectrons at altitudes above that where the flux is maximum are on the average more energetic than those below that altitude. The flux of photoelectrons escaping to the protonosphere at dawn was found to be 2.6 × 108 cm?2 sec?1, while the escaping flux at noon was found to be 1.5 × 108 cm?2 sec?1. The corresponding escaping energy fluxes are: 4.4 × 109 eV cm?2 sec?1 and 2.7 × 109 eV cm?2 sec?1. 相似文献
17.
D.G. Torr Marsha R. Torr James C.G. Walker R.A. Hoffman 《Planetary and Space Science》1975,23(1):15-26
A simple model of the motion of charged particles in the closed field line magnetic field for L ? 4·5 is used together with Injun 3 measurements of 40 keV precipitated electrons made in the northern hemisphere to estimate theoretically the extent of electron precipitation, the energy input and the 3914 Å airglow in the South Atlantic geomagnetic anomaly. Using average values of the northern hemisphere precipitated electron flux, two regions of significantly enhanced electron precipitation are found in the southern hemisphere. One occurs in the region 10–20°E and 40–50°S, with L ≈ 2, and the second near 30°E and 65°S, with L ≈ 4.5. Approximately 0.04 erg cm?2 sec?1 are deposited by 40 keV electrons for 50 per cent of the time in the first region and half that amount in the second. This increases to ～0·1 and 0·02 erg cm?2 sec?1 respectively for 15 per cent of the time for near sunspot minimum conditions. The results show a gradual increase in precipitation on the western side of the anomaly followed by a rapid increase and sudden cut-off in precipitation within a few degrees west of minimum B. The flux on L = 2 reaches a “spike” in the southern hemisphere ～f35 times greater than the average flux precipitated on L = 2 in the northern hemisphere. This increase in precipitation arises from the loss of “trapped” particles to the atmosphere where the mirror heights are lowest. 相似文献
18.
Results of analysis of about 150 autocorrelation functions are presented for the period from about 2300 hr on 5 October to about 1200 hr on 7 October 1967. A large percentage concentration of helium ions are observed. It reaches a value as high as 50 per cent with a maximum at around 800 km. Downward heat fluxes deduced from the temperature variations yield a value of about 2–2.5 × 109 eV cm?2 sec?1 during the period 1200–1600 hr and a value of about 1.5 × 108 eV cm?2 sec?1 during the period 0100–0400 hr at night. These agree well with other measurements. The O+ ions are found not to be in diffusive equilibrium, and from the O+ fluxes and the electron density profiles, the O+ drift velocity has been estimated. It is found that the speed can be as high as 1–5 × 103 cm sec?1 even at altitudes as high as 700 km. 相似文献
19.
The E ring associated with the Kronian moon Enceladus has a lifetime of only a few thousand years against sputteringly by slow corotating O ions. The existence of the ring implies the necessity for a continuous supply of matter. Possible particle source mechanisms on Enceladus include meteoroidal impact ejection and geysering. Estimates of ejection rates of particulate debris following small meteoroid impact are on the order of 3 × 10?18 g cm?2 sec?1, more than an order of magnitude too small to sustain the ring. A geyser source would need to generate a droplet supply at a rate of approximately 10?16 g cm?2 sec? in order to account for a stable ring. Enceladus and the ring particles also directly supply both plasma and vapor to space via sputtering. The absence of a 60 eV plasma at the Voyager 2 Enceladus L-shell crossing, such as might have been expected from sputtering, cannot be explained by absorption and moderation of plasma ions by ring particles, because the ring is too diffuse. Evidently, the effective sputtering yield in the vicinity of Enceladus is on the order of, or smaller than, 0.4, about an order of magnitude less than the calculated value. Small scale surface roughness may account for some of this discrepancy. 相似文献
20.