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NASA NTRS1974

Search by Mariner 10 for electrons and protons accelerated in association with Venus

Results of a search, with the aid of Mariner 10, for electrons and protons produced by acceleration occurring from the interaction of the solar wind and interplanetary field with the Venusian ionosphere. No evidence was found for Venus-associated particle fluxes with instrumentation capable of measuring flux variations approximately 1000 times smaller than those of the Mariner 5 detectors for charged particles, although the Mariner 10 measurements were made in the presence of an interplanetary particle flux that was extremely stable and characteristic of minimum solar activity. In addition, no evidence was obtained for electron or proton fluxes in the vicinity of the planet, nor any evidence for electron bursts in or near the observed bow shock, thus giving rise to the conclusion that Venus has no magnetosphere.-

Simpson, J. A.↗
NASA NTRS1974

Cloud base levels for Jupiter and Venus and the heteromolecular nucleation theory

For purified binary gas mixtures like NH3-H2O or HCl-H2O, partial pressures appreciably greater than the two saturation partial pressures are needed to condense the gas mixture into small solution droplets (homogeneous heteromolecular nucleation). Thus without foreign nuclei, clouds are not as easily formed as in the theories of Lewis; the latter should be valid only if large condensation nuclei are available. We calculate here from classical homogeneous heteromolecular nucleation theory the threshold partial pressures necessary to achieve droplet nucleation for the gas mixtures NH3-H2O (Jupiter), HCl-H2O (Venus), H2SO4-H2O (Venus), and C2H5OH-H2O (laboratory).

Stauffer, D.↗
NASA NTRS1974

The Regulus occultation light curve and the real atmosphere of Venus

An inversion of the light curve observed during the July 7, 1959, occultation of Regulus by Venus leads to the conclusion that the light curve cannot be reconciled with models of the Venus atmosphere based on spacecraft observations. The event occurred in daylight and, under the subsequently difficult observation conditions, it seems likely that the Regulus occultation light curve is marred by a systematic errors in spite of the competence of the observers involved.

Veverka, J.↗
NASA NTRS1974

The ionospheres of Mars and Venus

Observations made by spacecraft in the Mariner and Venera series have provided considerable knowledge of the structure of the ionospheres and atmospheres of Mars and Venus. This paper begins with brief but complete discussions of these measurements and their interpretations. The principles for constructing models of ionospheres are presented from the standpoint of mass, momentum, and energy conservation. The relevant ion chemistry is presented, and the meaning and use of plasma scale heights are discussed. The models discussed are the model of Cloutier and co-workers; the models of Banks and Axford, of Whitten, and of Herman and co-workers; the model developed by McElroy and Strobel to account for the nighttime ionosphere of Venus; and the models developed by a number of investigators for the thermal structure of the Martian and Venusian ionospheres.

Whitten, R. C.↗
NASA NTRS1974

Atmosphere of Venus: Implications of Venera 8 sunlight measurements

Venera 8 measurements of solar illumination within the atmosphere of Venus are quantitatively analyzed by using a multilayer model atmosphere. The analysis shows that there are at least three different scattering layers in the atmosphere of Venus and the total cloud optical thickness is about 10 or greater. However, because of the nature of the observations, it is not possible to determine the vertical distribution of absorbed solar energy, which would reveal the drive for the atmospheric dynamics and the strength of the greenhouse effect. Future spacecraft observations should be designed to (1) measure both upward and downward solar fluxes, (2) include measurements of the highest cloud layers, and (3) employ narrow-band and broad-band sensors.-

Lacis, A. A.↗
NASA NTRS1974

Spatial distribution of polarization over the disks of Venus, Jupiter, Saturn, and the moon

The method of photographic subtraction, which superposes positive and negative photographs taken with the analyzer rotated through 90 deg, is used to analyze polarization photographs of Venus, Jupiter, Saturn, and the moon. For Venus, near 90 deg phase angle, variation in polarization in ultraviolet light appears to correspond generally with the position of the cloud markings. The northern hemisphere of Saturn shows higher polarization in blue light than does the rest of the planet. The polarization of the moon is shown to deviate significantly from Umov's law for reciprocity of polarization and reflectivity in certain regions.

Fountain, J. W.↗
NASA NTRS1974

Observations of small-scale turbulence in the atmosphere of Venus by Mariner 5

Information regarding small-scale turbulence in the Venus atmosphere is important and desirable because it contributes to understanding of the atmosphere's circulation. It is demonstrated that the radio occultation data of a flyby spacecraft such as Mariner 5 can provide valuable information on turbulence in the Venus atmosphere. Unlike previous studies of the Mariner 5 data, this paper is based on the frequency spectrum rather than the variance of the log-amplitude fluctuations. The excellent agreement between the processed and previously derived theoretical spectra furnishes strong evidence that the Mariner 5 fluctuations are primarily turbulence-induced. It is seen that, above 35 km, turbulence is strongest in the vicinity of 45 and 60 km, and that the outer scale of turbulence is of the order of 100 m. Comparison with the results obtained from the Venera missions is also discussed.

Woo, R.↗
NASA NTRS1974

Polarization of Venus: Observations of short-term quasi-periodic variations

Observations of the short period variations in ultraviolet polarization and carbon dioxide line intensity for the atmosphere of the planet Venus are discussed. Theoretical polarization-phase curves for the integrated disk of Venus are developed. The amplitude of the short-term variation in the polarization as a function of wavelength is analyzed. Curves are developed to show the relationship between percent polarization and phase angle for various wavelengths.

Bowell, E.↗
NASA NTRS1975

Comments on "Venus' spectroscopic phase variation: Implications of the Mariner 10 photographs

From a misinterpretation of Mariner 10 pictures, Chamberlain (1974) constructed a model in which he used horizontal variations in the Venus atmosphere to explain the phase-variation of CO2 absorption at small phase angles. Published observations of spatial variations in CO2 absorption on Venus show that they are too small to explain the phase effect. The question of uniqueness that is, if more than one model can explain the phase-effect observations is discussed. Before this question can be answered, a realistic model that does account for the data must be constructed. No such calculations exist.

Young, A. T.↗
NASA NTRS1975

On the reality of the Venus winds

The Venera measurements of wind speed along with the Mariner measurements of lower-region of strong turbulence are evidence for a wide band of variable high speed retrograde horizontal winds which girdle Venus at the equator. In one interpretation of the Mariner 10 UV photographs, the 20km region above the top of the visible cloud is characterized by variable high-speed retrograde horizontal winds which orbit Venus with an average period of 4 earth days, and by many features indicating vertical convection. This suggests that the Venera-Mariner band of winds at 45km extends to the top of the UV cloud and beyond, and that the upper-region of strong turbulence detected by the Mariners may result from vertical convection currents carried along by high speed horizontal winds. In another interpretation, the predominate motions are attributed to wavelike disturbances with a 4-day period. For this case the upper-region of strong turbulence may be due in large part to vertical wind-shear resulting from a rapid decrease in wind speed within a relatively short distance about the Venera-Mariner band of high speed winds.

Ainsworth, J. E.↗
NASA NTRS1974

Aircraft observations of Venus' near-infrared reflection spectrum - Implications for cloud composition

A comparison of aircraft-based measurement data on Venus' near-infrared (1.2- to 4.1-micron) reflection spectrum with computer generated spectra of a number of cloud candidates shows a 75-% or more concentrated water solution of sulfuric acid to give the only acceptable match to the profile of Venus' strong 3-micron absorption feature. However, the measurement data obtained also show a modest decline in reflectivity from 2.3-micron to 1.2-micron wavelength, which is inconsistent with the flat spectrum of sulfuric acid in this spectral region. It is hypothesized that this decline is due to impurities in the sulfuric acid droplets.

Pollack, J. B.↗
NASA NTRS1974

Mariner 10 mission to Venus and Mercury

The unmanned spacecraft Mariner 10 was launched on November 3, 1973. Investigations conducted during the first part of its journey included studies carried out to calibrate the instruments in the well-known environment of the earth-moon system. Images of the north polar region of the moon were obtained and observations of the comet Kohoutek were made. Mariner confirmed the presence of a Venus bowshock. Information obtained by the spacecraft about the Venus atmosphere is considered. On March 29, 1974, Mariner 10 passed across the night side of Mercury only 703 kilometers above the planetary surface. It was found that Mercury is a moon-like body, heavily cratered, and with large, flat, circular basins similar to those on the moon and Mars.

Giberson, W. E.↗
NASA NTRS1974

Radio interferometry of Venus at short wavelengths

From short wavelength interferometry of Venus interpreted on the basis of the physical structure and bulk composition of its atmosphere as given by spacecraft measurements, evidence for the presence of a source of opacity in addition to CO2 is found. This opacity presumably is due to unknown minor constituents of the atmosphere of Venus.

Janssen, M. A.↗
NASA NTRS1975

Is the four-day 'rotation' of Venus illusory

An overlooked systematic error exists in the apparent radial velocities of solar lines reflected from regions of Venus near the terminator, owing to a combination of the finite angular size of the sun and its large equatorial velocity of rotation. This error produces an apparent, but fictitious, retrograde component of planetary rotation, typically on the order of 40 m/sec. Spectroscopic, photometric, and radiometric evidence against a 4-day atmospheric rotation is reviewed. The bulk of the somewhat contradictory evidence seems to favor slow motions, on the order of 5 m/sec, in the atmosphere of Venus; the 4-day 'rotation' may be due to a traveling wavelike disturbance, not bulk motions, driven by the UV albedo differences.

Young, A. T.↗
NASA NTRS1975

The aeronomy of the upper atmosphere of Venus

It is shown that rather tight constraints can be placed on the mixing ratio of atomic oxygen in the upper atmosphere of Venus, as well as that of CO and molecular oxygen, unless extraordinary processes which lead to a very large efflux of hydrogen from the planet are postulated. The analysis conducted is similar to the investigation carried out for the earth by Liu and Donahue (1974). If Jeans escape provides the main escape mode for hydrogen from Venus, the concentration ratio of atomic oxygen to carbon dioxide at 130 km is much less than 1% and some mechanism other than resonance scattering plus photoelectron excitation must account for the oxygen airglow.

Liu, S. C.↗
NASA NTRS1975

High-dispersion spectroscopic observations of Venus during 1968 and 1969. II - The carbon-dioxide band at 8689 A

Results are reported for an extensive series of high-resolution spectroscopic observations of the CO2 band at 8689 A in the atmosphere of Venus which were made over a period of one year at a dispersion of 2 A/mm for Venus phase angles varying from 10 to 126 deg. The equivalent widths of lines in the band are measured, the rotational temperature is calculated, and the CO2 abundance over various areas on the planet is determined. The results are compared with those of previous observations of the CO2 bands at 8689, 7820, and 7883 A, and good agreement is found regarding the temperatures and abundances derived for the different bands. It is concluded that the CO2 abundance varies over the planet and that its distribution does not remain constant with time.

Schorn, R. A. J.↗
NASA NTRS1975

Our present view of Mercury and Venus

The discipline of planetology received a quantum jump in new information on the planets Mercury and Venus from the Mariner 10 spacecraft. A detailed look at the ultraviolet markings in the upper atmosphere of Venus and their attendant motion has stimulated a considerable reevaluation of theories concerning the circulation, composition, and nature of this planet's upper atmosphere. The geologic history of Mercury as revealed by Mariner 10's television science data, from two close flybys, has challenged the prevalent theories of planetary evolution. The Mercury surface morphology and optical properties resemble those of the moon and seem to record a similar sequence of events despite their differences in density and proximity to both the sun and the asteroid belt.

Danielson, G. E., Jr.↗
NASA NTRS1975

He 584 A airglow emission from Venus - Mariner 10 observations

Observations were made across the bright limb of Venus by the ultraviolet spectrometer on Mariner 10 as the spacecraft flew by this planet on February 5, 1974. The altitude variation of the brightness of 584-A emission is interpreted with respect to the helium distribution in the atmosphere. Resonance scattering of solar radiation is considered as the source of this emission. The comparison of model calculations with the data shows that the observed altitude profile is consistent with a He density of about 2 million/cu cm at 145-km altitude and with an exospheric temperature of the order of 375 K. If the major loss of helium is by solar-wind scavenging only, the present helium content on Venus can be maintained by an outgassing rate of about 200,000 per sq cm per sec from the planet crust. By using these neutral helium measurements, it is found that the He(+) ion density in the outer ionosphere would be of the order of 200/cu cm.

Kumar, S.↗