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It is proposed that Saturn's electrostatic discharges (SED) might be generated in the planet's equatorial atmosphere, perhaps as lightning from a storm system. The 10h10m periodicity of the signal envelope duplicates that of Saturn's equatorial jet. The rings shield the atmosphere from solar EUV photons, and thereby substantially reduce the local ionospheric cutoff frequency to allow low-frequency SED to leak out. Many of the unusual properties of SED could be explained in terms of changes in the storm system, the relative spacecraft position in the beaming pattern of the source, local refraction of the signal by the highly disturbed ionosphere, and the influence of the ring particles on the highest frequency component of SED. A comparison of SED with planetary lightning on other planets shows that the two are similar in general character and some time behavior; the power output of SED may be higher than most planetary lightnings but that is unclear because of uncertainties in the measurements and variations in the signal's spectrum. Our simple discussion suggests that lightning could be a viable source for SED and that exotic ring mechanisms are not necessarily required. 相似文献
3.
Photographic observations of the nightside of Jupiter by the Voyager 1 spacecraft show the presence of extensive lightning activity. Detection of whistlers by the plasma wave analyzer confirms the optical observations and implies that many flashes were not recorded by the Voyager camera because the intensity of the flashes was below the threshold sensitivity of the camera. Measurements of the optical energy radiated per flash indicate that the observed flashes had energies similar to that for terrestrial superbolts. The best estimate of the lightning energy dissipation rate of 0.4 × 10?3 W/m2 was derived from a consideration of the optical and radiofrequency measurements. The ratio of the energy dissipated by lightning compared to the convective energy flux is estimated to be between 0.27 × 10?4 and 0.5 × 10?4. The terrestrial value is 1 × 10?4. 相似文献
4.
Although lightning has not yet been observed in Titan's atmosphere, the presence of condensable vapors and the deposition of a significant amount of solar energy at the surface suggest the possibility of lightning activity. Based on an understanding of the relationship of lightning activity to the amount of convective energy available on Titan, a lightning energy dissipation rate of 4 × 10?6, W/m2 can be expected. This value is much lower than that for Earth or Jupiter, and is a result of both the reduced solar flux at Titan and the absorption of sunlight by the aerosols that lie above the convective layer. For this dissipation rate, the amount of HCN and C2N2 produced by lightning should be greater than that by solar UV, but could be less than that produced by electron precipitation and galactic cosmic rays. Equilibrium calculations indicate that large mole fractions of elemental solid phase carbon will also be produced. Using a simplified model of aerosol formation, coagulation, and settling, it is estimated that a lightning-produced aerosol could have a typical optical depth of 10?2, with values as high as 0.1. The accumulation of soot over geological time might reach a meter or more in depth. 相似文献
5.
The lightning energy dissipation rate on Jupiter from Voyager's observation is used, together with shock-tube experimental results and reasonable eddy diffusion coefficients for the various atmospheric layers, to compute the column abundances of lightning-produced CO, C2H2, and HCN. Shock-tube experiments on the hydrogenation of CO clearly rule out chemical “freezing” of CO at the 1064°K and 400-bar level and its subsequent upwelling to the upper atmosphere. Also, lightning in the water cloud cannot produce enough CO to meet its observed abundance. Hence, the CO is formed from an external source of oxygen or water. The production of acetylene both by lightning above the water cloud and by startospheric methane photolysis is required to maintain its observed abundance against destruction processes. This explains the decrease in the C2H2/C2H6 ratio from the equator to the pole, as observed in the IR. HCN production by lightning above the water cloud is sufficient to account for its observed abundance and meets the observational requirement of a tropospheric HCN source. 相似文献
6.
Mario Rabinowitz 《Astrophysics and Space Science》1998,262(4):391-410
Small, quiescent black holes can be considered as candidates for the missing dark matter of the universe, and as the core
energy source of ball lightning. By means of gravitational tunneling, unidirectional radiation is emitted from black holes
in a process much attenuated from that of Hawking radiation, P, which has proven elusive to detect. Gravitational tunneling
emission is similar to electric field emission of electrons from a metal in that a second body is involved which lowers the
barrier and gives the barrier a finite rather than infinite width. Hawking deals with a single isolated black hole. The radiated
power here is P ∝ e-2Δγ P, where e-2Δγ is the transmission probability.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
Based on recent evidence that oxide grains condensed from a plasma will contain oxygen that is mass‐independently fractionated compared to the initial composition of the vapor, we present a first attempt to evaluate the potential magnitude of this effect on dust in the primitive solar nebula. This assessment relies on previous studies of nebular lightning to provide reasonable ranges of physical parameters to form a very simple model to evaluate the plausibility that lightning could affect a significant fraction of nebular dust and that such effects could cause a significant change in the oxygen isotopic composition of solids in the solar nebula over time. If only a small fraction of the accretion energy is dissipated as lightning over the volume of the inner solar nebula, then a large fraction of nebular dust will be exposed to lightning. If the temperature of such bolts is a few percent of the temperatures measured in terrestrial discharges, then dust will vaporize and recondense in an ionized environment. Finally, if only a small average decrease is assumed in the 16O content of freshly condensed dust, then over the last 5 Myr of nebular accretion the average Δ17O of the dust could increase by more than 30 per mil. We conclude that it is possible that the measured “slope 1” oxygen isotope line measured in meteorites and their components represents a time‐evolution sequence of nebular dust over the last several million years of nebular evolution where 16O‐rich materials formed first, then escaped further processing as the average isotopic composition of the dust gradually became increasingly depleted in 16O. 相似文献
8.
Ulyana A. Dyudina Andrew P. Ingersoll Carolyn C. Porco William Kurth Anthony Del Genio Joseph Ferrier 《Icarus》2007,190(2):545-555
We report on Cassini Imaging Science Subsystem (ISS) data correlated with Radio and Plasma Wave Science (RPWS) observations, which indicate lightning on Saturn. A rare bright cloud erupt at ∼35° South planetocentric latitude when radio emissions (Saturn Electrostatic Discharges, or SEDs) occur. The cloud consisting of few consecutive eruptions typically lasts for several weeks, and then both the cloud and the SEDs disappear. They may reappear again after several months or may stay inactive for a year. Possibly, all the clouds are produced by the same atmospheric disturbance which drifts West at 0.45 °/day. As of March 2007, four such correlated visible and radio storms have been observed since Cassini Saturn Orbit Insertion (July 2004). In all four cases the SEDs are periodic with roughly Saturn's rotation rate (h10m39), and show correlated phase relative to the times when the clouds are seen on the spacecraft-facing side of the planet, as had been shown for the 2004 storms in [Porco, C.C., and 34 colleagues, 2005. Science 307, 1243-1247]. The 2000-km-scale storm clouds erupt to unusually high altitudes and then slowly fade at high altitudes and spread at low altitudes. The onset time of individual eruptions is less than a day during which time the SEDs reach their maximum rates. This suggests vigorous atmospheric updrafts accompanied by strong precipitation and lightning. Unlike lightning on Earth and Jupiter, where considerable lightning activity is known to exist, only one latitude on Saturn has produced lightning strong enough to be detected during the two and a half years of Cassini observations. This may partly be a detection issue. 相似文献
9.
Vladimir A. Krasnopolsky 《Icarus》2006,182(1):80-91
High-resolution spectra of Venus and Mars at the NO fundamental band at 5.3 μm with resolving power ν/δν=76,000 were acquired using the TEXES spectrograph at NASA IRTF on Mauna Kea, Hawaii. The observed spectrum of Venus covered three NO lines of the P-branch. One of the lines is strongly contaminated, and the other two lines reveal NO in the lower atmosphere at a detection level of 9 sigma. A simple photochemical model for NO and N at 50-112 km was coupled with a radiative transfer code to simulate the observed equivalent widths of the NO and some CO2 lines. The derived NO mixing ratio is 5.5±1.5 ppb below 60 km and its flux is . Predissociation of NO at the (0-0) 191 nm and (1-0) 183 nm bands of the δ-system and the reaction with N are the only important loss processes for NO in the lower atmosphere of Venus. The photochemical impact of the measured NO abundance is significant and should be taken into account in photochemical modeling of the Venus atmosphere. Lightning is the only known source of NO in the lower atmosphere of Venus, and the detection of NO is a convincing and independent proof of lightning on Venus. The required flux of NO is corrected for the production of NO and N by the cosmic ray ionization and corresponds to the lightning energy deposition of . For a flash energy on Venus similar to that on the Earth (∼109 J), the global flashing rate is ∼90 s−1 and ∼6 km−2 y−1 which is in reasonable agreement with the existing optical observations. The observed spectrum of Mars covered three NO lines of the R-branch. Two of these lines are contaminated by CO2 lines, and the line at 1900.076 cm−1 is clean and shows some excess over the continuum. Some photochemical reactions may result in a significant excitation of NO (v=1) in the lowest 20 km on Mars. However, quenching of NO (v=1) by CO2 is very effective below 40 km. Excitation of NO (v=1) in the collisions with atomic oxygen is weak because of the low temperature in the martian atmosphere, and we do not see any explanation of a possible emission of NO at 5.3 μm. Therefore the data are treated as the lack of absorption with a 2 sigma upper limit of 1.7 ppb to the NO abundance in the lower atmosphere of Mars. This limit is above the predictions of photochemical models by a factor of 3. 相似文献
10.
The effect of excess hydrogen on the synthesis of amino acids, by high-temperature shock waves in a hydrogen/methane/ammonia/water vapor mixture, was studied experimentally. The energy efficiency results, together with the best estimate of the lightning energy dissipation rate on Jupiter, from the Voyager data, were used to calculate an upper limit to the rate of amino acid production by lightning in the Jovian water clouds. Using reasonable values for the eddy diffusion coefficients within and below the water clouds, the column abundance of lightning-produced amino acids in the clouds was estimated to be 6.2 × 10?6 cm-am. Hence, concentration of amino acids in water droplets would be 8 × 10?8 mole liter?1. 相似文献
11.
A Monte Carlo program by Thomason and Krider has been adapted to the Venus cloud geometry and optical properties. If lightning flashes occur within or just below the clouds, the fraction of photons of visible light escaping to space is 0.1–0.4, depending on the location of the flash. For flashes near the surface, only one blue photon in 104 was found to escape; about 5% of the red ones are transmitted. Failure of the Pioneer Venus Orbiter to unambiguously detect optical lightning signals from space is not due to attenuation by the atmosphere and clouds. In any case, lightning is not acceptable as an explanation for ashen light. 相似文献
12.
A. Bar-nun 《Icarus》1980,42(3):338-342
The effects of the newly discovered thunderstorms on Venus upon the nitrogen and carbon species in its atmosphere were calculated. An Earth-like lightning frequency of 100 sec?1 was used for Venus, in accord with recent optical measurements by Pioneer-Venus (W. J. Borucki, J. W. Dyer, G. Z. Thomas, J. C. Jordon, and D. A. Comstock, submitted for publication). The rate of NO production by thunder shock waves, 2.5 × 1011 g year?1, is about an order of magnitude smaller than on the Earth. But on Venus, in the absence of precipitation, which is the major removal mechanism of odd nitrogen from the Earth's atmosphere, the mixing ratios of odd nitrogen species might be considerably higher. The global CO production is governed by CO2 photolysis rather than by CO2 pyrolysis by lightning. However, thunderstorms produce about 2.5 × 1011 g year?1 of CO in the cloud layer, far from the high altitude CO2 photolysis region. 相似文献
13.
Monte Carlo Radiative Transfer Modeling of Lightning Observed in Galileo Images of Jupiter 总被引：1，自引：0，他引：1
We study lightning on Jupiter and the clouds illuminated by the lightning using images taken by the Galileo orbiter. The Galileo images have a resolution of ∼25 km/pixel and are able to resolve the shape of single lightning spots, which have half widths (radii) at half the maximum intensity in the range 45-80 km. We compare the shape and width of lightning flashes in the images with simulated flashes produced by our 3D Monte Carlo light-scattering model.The model calculates Monte Carlo scattering of photons in a 3D opacity distribution. During each scattering event, light is partially absorbed. The new direction of the photon after scattering is chosen according to a Henyey-Greenstein phase function. An image from each direction is produced by accumulating photons emerging from the cloud in a small range (bins) of emission angles. The light source is modeled either as a point or a vertical line.A plane-parallel cloud layer does not always fit the data. In some cases the cloud over the light source appears to resemble cumulus clouds on Earth. Lightning is estimated to occur at least as deep as the bottom of the expected water cloud. For the six flashes studied, we find that the clouds above the lightning are optically thick (τ>5). Jovian flashes are more regular and circular than the largest terrestrial flashes observed from space. On Jupiter there is nothing equivalent to the 30-40-km horizontal flashes that are seen on Earth. 相似文献
14.
Repeated searches for optical evidence of lightning across Venus nightside regions reported as exhibiting almost incessant activity have failed to detect any evidence of lightning. Owing to the extensive nature of these investigations, the negative results contribute strongly to the interpretation that the plasma noise initially attributed to a lightning source is instead stimulated by interaction of the solar wind and draped interplanetary magnetic field with the nightside ionosphere. 相似文献
15.
Laser-induced plasmas in various gas mixtures were used to simulate lightning in other planetary atmospheres. This method of simulation has the advantage of producing short-duration, high-temperature plasmas free from electrode contamination. The laser-induced plasma discharges in air are shown to accurately simulate terrestrial lightning and can be expected to simulate lightning spectra in other planetary atmospheres. Spectra from 240 to 880 nm are presented for simulated lightning in the atmospheres of Venus, Earth, Jupiter, and Titan. The spectra of lightning on the other giant planets are expected to be similar to that of Jupiter because the atmospheres of these planets are composed mainly of hydrogen and helium. The spectra of Venus and Titan show substantial amounts of radiation due to the presence of carbon atoms and ions and show CN Violet radiation. Although small amounts of CH4 and NH3 are present in the Jovian atmosphere, only emission from hydrogen and helium is observed. Most differences in the spectra can be understood in terms of the elemental ratios of the gas mixtures. Consequently, observations of the spectra of lightning on other planets should provide in situ estimates of the atmospheric and aerosol composition in the cloud layers in which lightning is occuring. In particular, the detection of inert gases such as helium should be possible and the relative abundance of these gases compared to major constituents might be determined. 相似文献
16.
The photochemistry of the stratosphere of Venus was modeled using an updated and expanded chemical scheme, combined with the results of recent observations and laboratory studies. We examined three models, with H2 mixing ratio equal to 2 × 10?5, 5 × 10?7, and 1 × 10?13, respectively. All models satisfactorily account for the observations of CO, O2, O2(1Δ), and SO2 in the stratosphere, but only the last one may be able to account for the diurnal behavior of mesospheric CO and the uv albedo. Oxygen, derived from CO2 photolysis, is primarily consumed by CO2 recombination and oxidation of SO2 to H2SO4. Photolysis of HCl in the upper stratosphere provides a major source of odd hydrogen and free chlorine radicals, essential for the catalytic oxidation of CO. Oxidation of SO2 by O occurs in the lower stratosphere. In the high-H2 model (model A) the OO bond is broken mainly by S + O2 and SO + HO2. In the low-H2 models additional reactions for breaking the OO bond must be invoked: NO + HO2 in model B and ClCO + O2 in model C. It is shown that lightning in the lower atmosphere could provide as much as 30 ppb of NOx in the stratosphere. Our modeling reveals a number of intriguing similarities, previously unsuspected, between the chemistry of the stratosphere of Venus and that of the Earth. Photochemistry may have played a major role in the evolution of the atmosphere. The current atmosphere, as described by our preferred model, is characterized by an extreme deficiency of hydrogen species, having probably lost the equivalent of 102–103 times the present hydrogen content. 相似文献
17.
In order to investigate the hypothesis that dust aggregates were transformed to meteoritic chondrules by nebular lightning, we exposed silicatic and metallic dust samples to electrical discharges with energies of 120 to 500 J in air at pressures between 10 and 105 Pa. The target charges consisted of powders of micrometer-sized particles and had dimensions of mm. The dust samples generally fragmented leaving the major fraction thermally unprocessed. A minor part formed sintered aggregates of 50 to 500 μm. In a few experiments melt spherules having sizes ?180 μm in diameter (and, generally, interior voids) were formed; the highest spherule fraction was obtained with metallic Ni. Our experiments indicate that chondrule formation by electric current or by particle bombardment inside a discharge channel is unlikely. 相似文献
18.
Akiva Bar-Nun 《Icarus》1975,24(1):86-94
The presence of a considerable acetylene concentration on Jupiter, despite the fast rate of its photolytic hydrogenation, provides strong evidence for the operation of frequent and powerful thunderstorms in the Jovian atmosphere. Whereas acetylene regeneration can occur only during thunderstorms, the photolytically destroyed ammonia can be regenerated both in thunderstorms and in the low and hot atmospheric levels. A rate of Earthlike lightning strokes 104 times larger than on Earth is inferred from the calculated rate of acetylene's photolytic destruction. The rate of acetylene production by thunder shock waves and the products obtained from its photolytic hydrogenation can account for the large ethane concentration and the absence of ethylene. The yellow-brown acetylene polymer and the ruby-red polymers, obtained from thunder-produced hydrogen cyanide or cyanogen with ammonia, are likely contributor to the Jovian coloration. 相似文献
19.
A procedure is shown for extracting weak resonances from the responses of electromagnetic systems excited by electric discharges. The procedure, based on analysis of the late-time system response, is first checked using an analytical function and later with the data for the electric field generated by the computational simulation of Titan's atmosphere using the Transmission Line Matrix (TLM) method. Finally, the low frequency spectrum of the natural electric field in Titan's atmosphere sent by the mutual impedance sensor (MIP) included in the Huygens probe is analyzed employing this technique. The MIP sensor was initially designed to measure the horizontal component of the electric field during a quiet descent. Fortunately, the swinging that occurred during the descent allowed the MIP to measure the radial component of the electric field mixed with the horizontal one. Application of the late-time analysis technique shown in this paper confirms the signature of lightning reported by preliminary data observations, bringing out the expected eigenfrequencies of the Titan-ionosphere electromagnetic cavity, known as Schumann resonances. These resonances are the resonant frequencies of the lower TMr (transverse magnetic to r) modes, which are quasi-transverse electromagnetic modes because they present vertical or radial components of the electric field two orders of magnitude higher than the associated horizontal, azimuthal and zenithal, components. The sequence of Schumann resonances is unique for each celestial body with an ionosphere, since these resonances are fully determined by the dimensions of the planet or satellite and the corresponding atmospheric conductivity profile. Detecting these frequencies in an atmosphere is clear proof of electrical activity, since it implies the existence of an electromagnetic-energy source, which is essential to create and maintain them. 相似文献
20.
Cochran Anita L. Boice D. C. Barker Edwin S. Laffont Celine 《Earth, Moon, and Planets》1997,78(1-3):85-91
The ratio of CH4/CO in comets is an important indicator of the region of their formation. However, it is difficult to measure the quantity
of CH+. The Giotto Ion Mass Spectrometer experiment observed a quantity of CH+ which seemed inconsistent with the amount of CH+. Thus, it was proposed that a source of the CH+ was a distributed source in the dust. We tested this hypothesis by observing the CH emission strength in comet Hale-Bopp
as a function of dustiness. We see no strong correlation between the dust and the gas. Thus, for Hale-Bopp,dust is unlikely
to be a dominant source of CH.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献