Images Of Venus Research Articles

Correlation of simultaneous ultraviolet (0.36 μm) and infrared (8 to 14 μm) images of Venus

We present evidence for a correlation between features observed in simultaneous infrared (8 to 14 μm) and ultraviolet (0.36 μm) images obtained during Venus' 1975 and 1977 apparitions. The sense of the observed correlation is such that bright uv markings correspond to bright (warm) ir features, and similarly, dark uv markings correspond to dark (cool) ir features.

Infrared Image of Venus at the Time of Pioneer Venus Probe Encounter

An image of the infrared emission from the Earth-facing hemisphere of Venus was obtained at the time the Pioneer Venus probes penetrated the atmosphere. The thermal structure of the atmosphere at the 85-millibar level included regions of rapidly varying polar features, a solar-related postdawn warm area, and a nonsolar-fixed nighttime warm area. The probes succeeded in entering each of these three thermal regions.

The phase function of Venus cloud particles from Mariner 10 data

Mariner 10 images of Venus taken at several phase angles were photometrically reduced. The analysis shows that the phase function of the cloud particles is not isotropic, as had been deduced earlier from the brightness distribution on spacecraft images taken at a single phase angle, but has a broad minimum near 60° and is forward‐scattering. The scattering properties are in quantitative agreement with previous deductions from earth‐based polarization measurements by Hansen and his associates.

Venus: Further Evidence of Vortex Circulation

A space-time composite of polar stereographic ultraviolet images of Venus from Mariner 10 shows a remarkable circumpolar vortex. The vortex is characterized by a cloud which appears similar to dense terrestrial stratus having an albedo that is 50 percent higher. Spiral streaks converge into it from low latitudes, akin to the spiral bands of a hurricane. The bright visible polar cloud is not axisymmetric but has roughly an elliptical shape. The high brightness of the polar cloud suggests that it has a different origin from the rest of the Venus cloud cover.

Nature of the Atmospheric Dynamics on Venus from Power Spectrum Analysis of Mariner 10 Images

Mariner 10 Venus images are analyzed into power spectra of the brightness field for planetary zonal wavenumbers n≥3 and for latitudes from 55°–25°N. These spectra are examined for significant features and latitudinal variation as well as compared with cloud brightness distribution spectra similarly determined for the Earth. The Venus image spectra are found to have a systematic variation as a function of latitude. In the equatorial region the average power spectrum lm an approximately −2.7 power law behavior for n>5, while in midlatitudes the average spectrum is characterized by a slope of about −1.8 for n≥3. Although a flattening of the equatorial region spectrum for wavenumbers less than 5 is noted, no obvious peaks are superimposed on the general power law behavior of the Venus spectra. This is in contrast to the result for the Earth cloud brightness spectra, which exhibit a noticeable peak near wavenumber 5 or 6 for the midlatitude region. The Venus image spectra are further interpreted under the assumption that the UV cloud features serve as markers of large-scale dynamical processes and thus can reveal the characteristics of the eddy kinetic energy spectrum. Support for this assumption is provided by the results of a comparison of the cloud brightness spectra for the Earth with observed eddy kinetic energy spectra. The characteristics of the Venus spectra at low latitudes suggest that the observed clouds are in a region of high static stability in which the large-scale turbulence is essentially two-dimensional, and that the important energy sources are at the largest scales (n<5), with the spectrum exhibiting a slope close to the theoretically expected −3 value for an inertial subrange at larger wavenumbers. It is concluded that the less steep slope observed for the midlatitude spectrum is quite possibly the manifestation of the importance of barotropic eddy disturbances in that region.

Venus in motion

A comprehensive set of television pictures of Venus taken by the Mariner 10 spacecraft is presented. Included is a chronological sequence of television images illustrating the development, variety, and circulation of Venus upper-atmospheric phenomena as viewed in the near-ultraviolet. The higher-resolution images have been assembled into global mosaics to facilitate comparison. Figures and tables describing the imaging sequences have been included to provide a guide to the more complete set of 3400 Venus images on file at the National Space Science Data Center.

A Normalized View of Venus

A few Mariner 10 images of Venus have been 'normalized' to a standard scattering geometry using the exact solution by Chandrasekhar (1950) involving his H functions. The most striking feature of the normalized images is the bright polar ring or cap beyond about 50 deg latitude circle and a narrower brightness frequency distribution. The brightness variation along a meridian shows substantial axial symmetry on a large scale, and small-scale brightness variations over the planet are no more than about 10%. Inferences regarding the polar cloud tops in light of available evidence are discussed. The variation of mean brightness and of the ratio of mean square deviation of brightness to average brightness is comparable to the performance limits of the vidicon camera for the image sequence lasting about a day, so that the variation in distribution of dark and bright features over the planet and the UV albedo of the planet over about a day is small.

New Radar Image of Venus

A new radar image of Venus covering the latitude range 46 degrees to 75 degrees and the approximate longitude range 290 degrees to 10 degrees is shown. The resolution is approximately 20 kilometers.

Images of Venus by Infrared

Images of Venus by Infrared

Infrared imaging of Venus: 8–14 micrometers

High spatial resolution 8–14 μm images of Venus were obtained on March 6, 1974. The planet was at a phase angle of 112° with the morning terminator in view. Our images confirm the existence of a previously mapped flux anomaly near the south pole and show evidence of other infrared features, presumably transient in nature. Flux differences of 2–7% were measured, corresponding to brightnes temperature variations of roughly 1–3°K. The images also confirm the difference between polar and equatorial limb darkening. Finally, we present evidence for a night-day asymmetry in the flux, with the brightness temperature greater by about 2°K on the sunlit side.

On the Origin of Ultraviolet Contrasts on Venus

Models for the origin of the contrasts in the ultraviolet images of Venus are examined in an attempt to determine the physical differences between light and dark regions fundamental to a clear understanding of the apparent cloud motions. To evaluate the meaning of the wavelength dependence of the contrasts, an improved determination of the spherical albedo curve for Venus in the 0.225-1.06 micron range is made by fitting appropriate theoretical models to the observations of monochromatic magnitudes as a function of phase angle. It is shown that, because of differences between the spectral dependences of spherical albedo and contrasts, at least one major absorber other than the one causing the contrasts is almost certainly required. Several classes of models are compatible with present observational evidence. The contrasts and the absorption associated with them may in fact be occurring below, within or above the main visible cloud layer, and thus an unambiguous interpretation of the apparent cloud motions is not possible.

A radar image of Venus

Radar scans of Venus, performed at the Jet Propulsion Laboratory's Goldstone Tracking Station, have yielded a brightness map (attached) of a large portion of the surface. The bright area in the south (α) and the twin such areas in the north (β and δ) were dirst discovered by spectral analysis of radar echos. When range-gating is also applied, their shapes are revealed, and they are seen to be roundish and about 1000 km across. Although radar brightness can be the result of either intrinsic reflectivity or surficial roughness, polarization studies show these features to be rough (to the scale of the wavelength, 12.5 cm). Dark, circular areas can also be seen, many with bright central spots. The dark areas are probably smooth. The blurring of the equatorial strip is an artifact of the range-Doppler geometry; all resolution disappears at the equator. Another artifact of the method is the “ghost,” in the south, of the images of β and δ. Such ghosts appear only at the eastern and western extremes of the map. Data for this radar map were taken during the close approaches of spring, 1969, and fall, 1970. Another opportunity occurs in June of 1972. Venus will present the same aspect then, except that the spin axis will be inclined slightly toward Earth. We hope to take advantage of this opportunity to fill in the blurred equatorial zone and to remove the ghost images.

Imaging of Mercury and Venus from a flyby

This paper describes the results of study of an imaging experiment planned for the 1973 Mariner Venus/Mercury flyby mission. Scientific objectives, mission constraints, analysis of alternative systems, and the rationale for final choice are presented. Severe financial constraints ruled out the best technical alternative for flyby imaging, a film/readout system, or even significant re-design of previous Mariner vidicon camera/tape recorder systems. The final selection was a vidicon camera quite similar to that used for Mariner Mars 1971, but with the capability of real time transmission during the Venus and Mercury flybys. Real time data return became possible through dramatic increase in the communications bandwidth at only modest sacrifice in the quality of the returned pictures. Two identical long focal length cameras (1500 mm) were selected and it will be possible to return several thousand pictures from both planets at resolutions ranging from equivalent to Earthbased to tenths of a kilometer at encounter. Systematic high resolution ultraviolet photography of Venus is planned after encounter in an attempt to understand the nature of the mysterious ultraviolet markings and their apparent 4- to 5-day rotation period. Full disk coverage in mosaics will produce pictures of both planets similar in quality to Earthbased telescopic pictures of the Moon. The increase of resolution, more than three orders of magnitude, will yield an exciting first look at two planets whose closeup appearance is unknown.

Our Astronomical Column

THE TOTAL SOLAR ECLIPSE OF AUGUST 9, 1896.—M. Deslandres, who was commissioned by the Bureau des Longitudes to proceed to Japan and make observations of the total solar eclipse visible there on August 9 last year, gives in La Nature for December 26 a short account of the expedition in general and a brief description of the results obtained. The station decided upon was the small port known as Yesashi, on the northern side of the island of Yézo, where the Japanese party under Prof. Terao and the American expedition were eventually located. During their stay of six weeks there were only eight fine days, so that the previous meteorological reports, which indicated the bad climatic conditions of the island at this season, were entirely corroborated. As we all know, the sky was cloudy during the time of totality, but the French party was more fortunate than the Norwegian observers, for their clouds were evidently not so dense as those which obscured the sun at Vadsö and Kiö. M. Deslandres, who was directing the observers under him, saw at a glance that it was useless to proceed in the programme previously arranged for under fine weather conditions. He therefore gave instructions that in the different instruments a single sensitive plate should be exposed for the entire duration of totality. Of the plates exposed, six showed the corona “plus ou moins fort,” while on the remainder nothing was seen after development. The negatives indicated dim extensions in the north-west, north-east, and south-west directions, but practically only the general distribution of the coronal light was shown. The images of Venus and Jupiter were also found recorded on two of the negatives. The eclipse of 1896, as M. Deslandres says, confirms the following law, indicated already to a certain extent in previous eclipses, namely, that the periodical variations of the spots which are followed by the prominences extend to the corona, and therefore also to the entire solar atmosphere.