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1.
A.T. Young 《Icarus》1979,37(1):297-300
The 3150-Å absorption on Venus, found by Barker et al. (1975, J. Atmos. Sci.32), may be due to carbon disulfide. The stability and thermodynamics of the carbon chalcogenides are briefly discussed.  相似文献   

2.
The Venus Express (VEX) mission has been in orbit to Venus for more than 4 years now. The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument onboard VEX observes Venus in two channels (visible and infrared) obtaining spectra and multi-wavelength images of the planet that can be used to sample the atmosphere at different altitudes. Day-side images in the ultraviolet range (380 nm) are used to study the dynamics of the upper cloud at 66–72 km while night-side images in the near infrared (1.74 μm) map the opacity of the lower cloud deck at 44–48 km. Here we present a long-term analysis of the global atmospheric dynamics at these levels using a large selection of orbits from the VIRTIS-M dataset covering 860 Earth days that extends our previous work (Sánchez-Lavega, A. et al. [2008]. Geophys. Res. Lett. 35, L13204) and allows studying the variability of the global circulation at the two altitude levels. The atmospheric superrotation is evident with equatorial to mid-latitudes westward velocities of 100 and 60 m s?1 in the upper and lower cloud layers. These zonal velocities are almost constant in latitude from the equator to 50°S. From 50°S to 90°S the zonal winds at both cloud layers decrease steadily to zero at the pole. Individual cloud tracked winds have errors of 3–10 m s?1 with a mean of 5 m s?1 and the standard deviations for a given latitude of our zonal and meridional winds are 9 m s?1. The zonal winds in the upper cloud change with the local time in a way that can be interpreted in terms of a solar tide. The zonal winds in the lower cloud are stable at mid-latitudes to the tropics and present variability at subpolar latitudes apparently linked to the activity of the South polar vortex. While the upper cloud presents a net meridional motion consistent with the upper branch of a Hadley cell with peak velocity v = 10 m s?1 at 50°S, the lower cloud meridional motions are less organized with some cloud features moving with intense northwards and southwards motions up to v = ±15 m s?1 but, on average, with almost null global meridional motions at all latitudes. We also examine the long-term behavior of the winds at these two vertical layers by comparing our extended wind tracked data with results from previous missions.  相似文献   

3.
In 1761, the Russian polymath Mikhail Vasilievich Lomonosov (1711–1765) discovered the atmosphere of Venus during its transit over the Sun’s disc. In this paper we report on experimental reenactments of Lomonosov’s discovery with antique refractors during the transit of Venus June 5–6, 2012. We conclude that Lomonosov’s telescope was fully adequate to the task of detecting the arc of light around Venus off the Sun’s disc during ingress or egress provided proper experimental techniques as described by Lomonosov in his 1761 report are employed.  相似文献   

4.
A. Aitta 《Icarus》2012,218(2):967-974
The mass and radius of our closest neighbour Venus are only slightly smaller than those of the Earth indicating a similarity in composition. However, the lack of self-sustained internal magnetic field in Venus points to a difference in the core structure. The theory of tricritical phenomena has recently been used to study solidification at the high pressures and temperatures of the Earth, revealing how the Earth’s core works. This theoretical approach is here applied to Venus. While keeping Venus’ mantle density similar to the Earth’s, one obtains the gravitational acceleration g inside Venus, its moment of inertia factor, the size, pressure and density of its core, together with the planet’s temperature profile. Mainly due to the temperature difference between the core–mantle boundary and surface being 21% smaller than on the Earth, and the 11.5% smaller gravitational acceleration, Venus’ Rayleigh number Ra parameterizing mantle convection is only 54% of the Earth’s, offering a possible explanation for the present lack of plate tectonics on Venus. The theory as discussed predicts that Venus is molten at the centre, with temperature about 5200 K, and has 8 mol.% impurities there, slightly more impurities than in the Earth’s inner core boundary fluid. These impurities are likely to be a combination of MgO and MgSiO3.  相似文献   

5.
Imaging spectroscopic observations of the Venus 1.27-μm O2 airglow were carried out with ground-based telescopes from 2002 to 2007. Spectral image cubes were taken with the Okayama Astrophysical Observatory/infrared imaging spectrometer (superOASIS), the Gunma Astronomical Observatory/near-infrared camera and NASA's Infrared Telescope Facility/cryogenic echelle spectrograph (CSHELL). The rotational temperature shows weak positive correlation with the airglow intensity. However, there are some regions that have almost same intensities but different temperatures. The intensities tend to decrease from the anti-solar point to the terminator besides local features. These results indicate that there are local strong downward flows superimposed on the subsolar-to-antisolar circulation.  相似文献   

6.
《Planetary and Space Science》2006,54(13-14):1398-1414
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7.
On its highly elliptical 24 h orbit around Venus, the Venus Express (VEX) spacecraft briefly reaches a periapsis altitude of nominally 250 km. Recently, however, dedicated and intense radio tracking campaigns have taken place in August 2008, October 2009, February and April 2010, for which the periapsis altitude was lowered to the 186–176 km altitude range in order to be able to probe the upper atmosphere of Venus above the North Pole for the first time ever in situ. As the spacecraft experiences atmospheric drag, its trajectory is measurably perturbed during the periapsis pass, allowing us to infer total atmospheric mass density at the periapsis altitude. A Precise Orbit Determination (POD) of the VEX motion is performed through an iterative least-squares fitting process to the Doppler tracking data, acquired by the VEX radioscience experiment (VeRa). The drag acceleration is modelled using an initial atmospheric density model (VTS3 model, Hedin, A.E., Niemann, H.B., Kasprzak, W.T., Seiff, A. [1983]. J. Geophys. Res. 88, 73–83). A scale factor of the drag acceleration is estimated for each periapsis pass, which scales Hedin’s density model in order to best fit the radio tracking data. Reliable density scale factors have been obtained for 10 passes mainly from the second (October 2009) and third (April 2010) VExADE campaigns, which indicate a lower density by a factor of about 1.8 than Hedin’s model predicts. These first ever in situ polar density measurements at solar minimum have allowed us to construct a diffusive equilibrium density model for Venus’ thermosphere, constrained in the lower thermosphere primarily by SPICAV-SOIR measurements and above 175 km by the VExADE drag measurements (Müller-Wodarg et al., in preparation). The preliminary results of the VExADE campaigns show that it is possible to obtain with the POD technique reliable estimates of Venus’ upper atmosphere densities at an altitude of around 175 km. Future VExADE campaigns will benefit from the planned further lowering of VEX pericenter altitude to below 170 km.  相似文献   

8.
Ground-based observations of Venus were made with a 5-cm drive Michelson interferometer during December 1970 and December 1973. The thermal emission spectrum of the central portion of the apparent disk was recorded from 450–1250 cm?1 with an apodized spectral resolution of 0.25 cm?1. All statistically significant sharp line absorption features in the spectrum have been identified with gaseous CO2. Comparison between the observed spectrum and a synthetic spectrum computed from a model atmosphere, assuming gaseous CO2 and a sulfuric acid haze as opacity sources, indicates good agreement. A broad diffuse absorption feature associated with the sulfuric acid haze is evident in the 870- to 930 cm?1 region. With the exception of the rotational lines of the 927-cm?1 CO2 band, the above feature appears as a continuum down to 0.25 cm?1 resolution. In the 750- to 1250-cm?1 range, the spectrum exhibits moderate thermal contrast with maximum brightness temperatures of 234–238°K occurring near 825 cm?1. These temperatures are in general agreement with previous measurements.  相似文献   

9.
The new ESA Venus Express orbiter is the first mission applying the probing technique of solar and stellar occultation to the atmosphere of Venus, with the SPICAV/SOIR instrument. SOIR is a new type of spectrometer used for solar occultations in the range 2.2-4.3 μm. Thanks to a high spectral resolving power R∼15,000-20,000 (unprecedented in planetary space exploration), a new gaseous absorption band was soon detected in the atmospheric transmission spectra around 2982 cm−1, showing a structure resembling an unresolved Q branch and a number of isolated lines with a regular wave number pattern. This absorption could not be matched to any species contained in HITRAN or GEISA databases, but was found very similar to an absorption pattern observed by a US team in the spectrum of solar light reflected by the ground of Mars [Villanueva, G.L., Mumma, M.J., Novak, R.E., Hewagama, T., 2008. Icarus 195 (1), 34-44]. This team then suggested to us that the absorption was due to an uncatalogued transition of the 16O12C18O molecule. The possible existence of this band was soon confirmed from theoretical considerations by Perevalov and Tashkun. Some SOIR observations of the atmospheric transmission are presented around 2982 cm−1, and rough calculations of line strengths of the Q branch are produced, based on the isotopic ratio measured earlier in the lower atmosphere of Venus. This discovery emphasizes the role of isotopologues of CO2 (as well as H2O and HDO) as important greenhouse gases in the atmosphere of Venus.  相似文献   

10.
Moroz  V. I.  Rodin  A. V. 《Solar System Research》2002,36(6):492-494
The qualitative characteristics of the vertical structure of the atmospheres of Venus and the Earth essentially differ. For instance, there are at least two, instead of one, zones with normal (thermal) convection on Venus. The first one is near the surface (a boundary layer); the second is at the altitudes of the lower part of the main cloud layer between 49 and 55 km. Contrary to the hypotheses proposed by Izakov (2001, 2002), the upper convective zone prevents energy transfer from the upper clouds to the subcloud atmosphere by anomalous turbulent heat conductivity. It is possible, however, that the anomalous turbulent heat conductivity takes part in the redistribution of the heat fluxes within the lower (subcloud) atmosphere.  相似文献   

11.
Four surveys in which the geometrical parameters were suitable for observations on weak scattering objects were carried out by the Venera 9, 10 orbiters using 3000–8000 Å spectrometers. The results of one survey can be explained by a dust layer at the height of sighting h = 100–700 km. Its absence in other sessions suggests a ring structure. The spectrum of dust scattering is a power function of the wavelength with the index varying from ?2.1 at 100km to ?1.3 at 500km. A method is proposed for obtaining the optical thickness, density and size distribution of dust particles from the scattering spectra. For m > 10?14 g the number of dust particles with a mass higher than m is proportional to m?1.3. The radial optical thickness τ is 0.7 × 10?5 at 5000 Å assuming the geometric thickness δ to be 100 km. The maximum optical thickness along the normal to the plane of the ring is τn = 4 × 10?6. The mass of the ring is 20 tons or 5 × 10?3 g cm?1 per unit circumference length; the maximum mass in a column normal to the ring plane is 10?10g cm?2; the maximum density (for δ = 100 km) is 10?17 g cm?3. A satellite of Venus gradually destroyed by temperature effects and by meteorite streams and plasma fluxes is suggested as the source of dust in the ring. One of 1 km radius could sustain such a ring for a billion years. The zodiacal light intensity near Venus is estimated.  相似文献   

12.
The region of the 8200 Å Band of H2O was studied in spectra of Venus obtained with an echelle grating spectrograph operated at an altitude of 14.6 km in the NASA Learjet research aircraft. Taking advantage of low foreground absorption, observing at a time of velocity quadrature, differential spectroscopy with respect to lunar spectra, and spectrum averaging, we establish a value of H2O of 3 ± 20 μ for the total path over the entire disk. This value differs from earlier studies of the integrated disk but supports the low values recently derived from infrared bands and by very high spectral resolution groundbased studies.  相似文献   

13.
The most significant aspect of the general circulation of the atmosphere of Venus is its retrograde super-rotation. A complete characterization of this dynamical phenomenon is crucial for understanding its driving mechanisms. Here we report on ground-based Doppler velocimetry measurements of the zonal winds, based on high resolution spectra from the UV–Visual Echelle Spectrograph (UVES) instrument at ESO’s Very Large Telescope. Under the assumption of predominantly zonal flow, this method allows the simultaneous direct measurement of the zonal velocity across a range of latitudes and local times in the day side. The technique, based on long slit spectroscopy combined with the high spatial resolution provided by the VLT, has provided the first ground-based characterization of the latitudinal profile of zonal wind in the atmosphere of Venus, the first zonal wind field map in the visible, as well as new constraints on wind variations with local time. We measured mean zonal wind amplitudes between 106 ± 21 and 127 ± 14 m/s at latitudes between 18°N and 34°S, with the zonal wind being approximately uniform in 2.6°-wide latitude bands (0.3 arcsec at disk center). The zonal wind profile retrieved is consistent with previous spacecraft measurements based on cloud tracking, but with non-negligible variability in local time (longitude) and in latitude. Near 50° the presence of moderate jets is apparent in both hemispheres, with the southern jet being stronger by ～10 m/s. Small scale wind variations with local time are also present at low and mid-latitudes.  相似文献   

14.
A study of the CO2 atmospheric emissions at 10-μm in the upper atmospheres of Mars and Venus is performed in order to explain a number of ground-based measurements of these emissions recently taken at very high spectral resolution in both planets. The measurements are normally used to derive atmospheric temperatures and winds, but uncertainties on the actual emission layers were so far a serious drawback for their correct interpretation. The non-LTE models used for Mars and Venus in the present analysis are entirely similar in order to perform consistent comparisons between the two planets. In particular, the same scheme of CO2 states and ro-vibrational bands are used, with similar assumptions on collisional routes and rate coef?cients, and also the same radiative transfer approximations. The emissions at 10-μm are produced in both atmospheres by the same excitation mechanism: radiative pumping of the CO2(0001) vibrational state by direct solar absorption(at 4.3 μm) and indirect absorption (at 2.7 μm, followed by collisional quenching). The computed radiances are specially strong in the upper mesosphere and lower thermosphere of the two planets during maximum solar illumination, producing a population inversion in such conditions with the lower states of the bands, the CO2 (1000) and CO2(0200). We obtained that other population inversions are also possible, involving higher energy CO2 states. The larger solar ?ux available on Venus is found to produce larger vibrational populations and stronger emissions than equivalent atmospheric layers on Mars, in agreement with the observations. A number of perturbation studies were used to determine the exact emission altitudes, or weighting function peaks, for usual nadir sounding. The sensitivity of the emission to non-LTE model uncertainties and to atmospheric variations in temperature and CO2 density is also presented. The dependence with the solar zenith angle and with the emission angle, as obtained with this model, could also be useful for guiding future observations.  相似文献   

15.
Mid-infrared images of almost the entire Venus nightside hemisphere obtained by the Longwave Infrared Camera (LIR) onboard Akatsuki on December 9 and 10, 2010 reveal that the brightness temperature of the cloud-top ranges from 237 K in the cold polar collars to 243 K in the equatorial region, significantly higher than the values obtained by Venera 15. Other characteristic features of the temperature distributions observed are zonal belt structures seen in the middle and low latitudes and patchy temperature structures or quasi-periodic streaks extending in a north–south direction in the northern middle latitudes and southern low latitudes.  相似文献   

16.
Edwin S. Barker 《Icarus》1975,25(2):268-281
The Venus water vapor line at 8197.71 Å has been monitored at several positions on the disk of Venus and at phase angles between 21° and 162°. Variations in the abundance have been found with spatial location, phase angle and time. During the 1972–1974 period, the total two-way absorption has varied from less than 1 to 77 μm of water vapor. The dependence on phase angle indicates 20 to 50 μm over the disk between 30° and 110° and small, but detectable amounts present during the rest of the observations. The spatial distribution with respect to the intensity equator is uniform with no location on the disk having systematically a higher or lower abundance. Comparisons made between the water vapor abundandances and the CO2 abundances determined from near-simultaneous observations of CO2 bands at the same positions on the disk of Venus show no correlation for the majority of the samples.  相似文献   

17.
The discovery of large, solid particles in the clouds of Venus is one of the most significant findings of Pioneer Venus because it means that a substantial mass of the clouds is composed of a material other than sulfuric acid. The evidence which suggests that solid particles form a distinctive size mode is reexamined. The mode is defined by a discontinuity between two size ranges of the Pioneer Venus particle size spectrometer. This discontinuity could represent a real size mode. However, it could also be an artifact of the measurement technique. R. G. Knollenberg (1984) discusses several possible instrumental effects which might have caused this discontinuity. It is hypothesized herein that such effects did occur and that the large particles are really the tail of the mode 2 sulfuric acid particle size distribution and are not a separate mode of solid particles. Using such a revised size distribution, it is shown that all of the Pioneer Venus and Venera optical data from the lower clouds can be explained with sulfuric acid droplets without introducing any solid particles. As a by-product of this analysis, it is also found that the upper clouds of Venus must contain a material with a higher refractive index than sulfuric acid. A small quantity of sulfur could account for this observation.  相似文献   

18.
The launch of the Soviet space probes Vega 1 and Vega 2 to explore Venus, including its atmosphere, and flyby Halley??s comet, a rare guest in the inner Solar System, added a vivid page to the history of space exploration. This paper is dedicated to Designer General Vyacheslav M. Kovtunenko.  相似文献   

19.
The Kelvin–Helmholtz instability gained scientific attention after observations at Venus by the spacecraft Pioneer Venus Orbiter gave rise to speculations that the instability contributes to the loss of planetary ions through the formation of plasma clouds. Since then, a handful of studies were devoted to the Kelvin–Helmholtz instability at the ionopause and its implications for Venus. The aim of this study is to investigate the stability of the two instability-relevant boundary layers around Venus: the induced magnetopause and the ionopause. We solve the 2D magnetohydrodynamic equations with the total variation diminishing Lax–Friedrichs algorithm and perform simulation runs with different initial conditions representing the situation at the boundary layers around Venus. Our results show that the Kelvin–Helmholtz instability does not seem to be able to reach its nonlinear vortex phase at the ionopause due to the very effective stabilizing effect of a large density jump across this boundary layer. This seems also to be true for the induced magnetopause for low solar activity. During high solar activity, however, there could occur conditions at the induced magnetopause which are in favour of the nonlinear evolution of the instability. For this situation, we estimated roughly a growth rate for planetary oxygen ions of about 7.6 × 1025 s−1, which should be regarded as an upper limit for loss due to the Kelvin–Helmholtz instability.  相似文献   

20.
《Planetary and Space Science》2006,54(13-14):1472-1481
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