Spectra Of Venus Research Articles

Spectroscopic observations of winds on Venus: I. Technique and data reduction

We present out methods of measurement and reduction of high-dispersion photographic spectra of Venus. Our preliminary results are consistent with slow direct or no rotation at the level we sample, and disagree strongly with a 4-day retrograde rotation. A serious systematic error, which affects much published work, is due to blending of solar lines in the sky with those reflected from the planet. This always tends to produce a spurious retrograde “rotation.” Only data obtained in a dark sky, or daytime observations from which the sky lines have been accurately subtracted, can be relied upon. All such data give low wind speeds.

The 12- to 20-micron spectrum of Venus: Implications for temperature and cloud structure

The spectrum of Venus was measured between approximately 500 and 800 cm −1 (12 to 20 μm) at a resolution of 3.12 cm −1 from the NASA C141 G.P. Kuiper Airborne Observatory on 22 and 24 February 1977. The spectrum clearly shows the detailed structure of CO 2 absorption in the vicinity of the ν 2 fundamental band at 667 cm −1. In addition, details of model fitting demonstrate the possibility for a cold and thin haze of sulfuric acid droplets along with an optically opaque cloud top near 250°K. Such clouds represent major differences from other H 2SO 4 main cloud deck models in the recent literature and may be indicative of changes in the vertical distribution of aerosols on a global scale. A retrieval of the temperature structure was obtained for a limited vertical region (0.63 to 1.6 mbar). The temperatures retrieved for pressures at or below 10 mbar are largely independent of the cloud model assumed and they are some 16 to 20°K warmer than the 1972 NASA model. All retrieved temperatures lie within the range of Mariner 5 and Mariner 10 radio occultation inversion results.

Identification of the UV nightglow from Venus

THE presence of atmospheric ultraviolet (UV) emission between 1,350 and 2,200 A from the nightside of Venus was first detected by instruments on board the Mariner 5 flyby1. Recently this emission was observed by the UV spectrometer on Pioneer Venus Orbiter at 2,068 A and identified by Stewart et al.2 as the (0, 0) Cameron band (a3Π-X1Σ) of CO. Their interpretation suggested a significant input of energy into the nightside thermosphere from the interaction of the solar wind with the planet. We report here the preliminary results of observations of the nightside spectrum of Venus made with the International Ultraviolet Explorer (IUE) observatory when Venus was near greatest elongation in January 1979. Three features are clearly seen in the spectra, and the spectral resolution of the instrument is adequate to identify them as bands of the nitric oxide δ(C2Π→X2Π) system rather than as Cameron bands. The δ-bands, present in the Earth's twilight and night time airglow spectra3, are produced by the radiative association of nitrogen and oxygen atoms and indicate a significant population of atomic nitrogen at or below the Venus turbopause.

The O2 (C³Δu → a¹Δg) bands in the nightglow spectrum of Venus

The 4000‐7000 Å nightglow spectrum of Venus, as reported by the Russian Venera 9 and 10 probes, is composed primarily of the 0‐v″ progression of the O2(c¹Σu− → X³Σg−) system. Recent observations in a laboratory afterglow system have established other O2 emissions in the same spectral region. Based on this work, closer scrutiny of the Venera spectrum reveals the presence of the C³Δu → a¹Δg 0−v′ progression, known as the Chamberlain system in the terrestrial airglow, and thus the C³Δu → a¹Δg bands are the first identified O2 emission that is common to both Earth and Venus.²

On the detectability of millimeter wavelength spectral lines from planetary atmospheres

This paper adopts a simple line-formation model to estimate detection limits on the fractional absorption produced by molecular lines in the spectra of the planets, when observed with the 14-m antenna and low-noise receivers of the Five College Radio Astronomy Observatory. The results, which can readily be adjusted for receiver and telescope characteristics of other observatories, indicate that three kinds of observing programs may prove fruitful: (1) programs to monitor temporal variations of the strong CO absorption in the spectrum of Venus and Mars; (2) searches for weak absorption lines of other molecules, which are particularly promising for Venus: and (3) efforts to measure broad features in the continuous spectra of Venus, and possibly Jupiter, produced by molecules deep in the planetary atmospheres. Except for delineation of broad features of NH3 and possibly H2O near 25 GHz, hardly any useful observations can be made at frequencies less than 60 GHz.

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.

The clouds of Venus: An anisotropic scattering model

The phase function ω ̃ (1 + a cos θ) for anisotropic scattering is applied to a homogeneous atmospheric model to ascertain the effects of anisotropy on the near-infrared spectrum of Venus. L. D. G. Young's equivalent widths for the 820 Å CO 2 band are analyzed to derive allowed combinations of CO 2 specific abundance, continuum albedo, pressure, and degree of anisotropy. From these combinations, values are derived for the photon mean-free path and total optical thickness of the clouds. The Venera 10 measurement of the transmitted flux at 7200 Å is then used in conjunction with spherical albedo requirements to reduce the range of possible solutions to the equivalent-width analysis. Through the application of approximate similarity relations, the “true” (i.e., anisotropic) atmospheric parameters are derived from the isotropic values. For an assumed Mie scatterer with an average anisotropy factor of 〈cos θ〉 = 0.7, the results indicate a total optical thickness of about 55 with a single-scattering albedo of 0.9992 to 0.9995.

Ultraviolet absorbers in the Venus clouds

Some absorption features in the ultraviolet spectrum of Venus observed by the OAO-2 cannot be interpreted in terms of H2SO4. Carbon suboxide polymer has a yellow colour and absorption at 2000 A. Fine graphite grains have an absorption band at about 2175 A as is well known in the case of the interstellar extinction curves. A mixture of these substances which is inevitably formed in the Venus atmosphere by photochemical reactions is the best candidate for explaining the Venus absorption features in the ultraviolet.

Temperature and pressure determinations in the Venus atmosphere by means of high-resolution spectra from 1 to 2.5 μm

Twenty-one bands of CO 2 and the 2-0 band of CO were analyzed for best temperature and pressure fits from Venus spectra obtained with the “Connes” interferometer at the Steward Observatory 2.25-m telescope during the spring of 1971. An average temperature of 241 ± 7°K, an effective pressure of 0.12 ± 0.06 atm, and an average two-way transmission abundance of 3 km-amagat were determined. No difference in temperature or pressure between hot bands, a double hot band, and regular bands was found. Our results were compared to model calculations for a reflecting layer and scattering atmosphere. The results indicate that, most likely, spectroscopic line formation occurs in a relatively clear space above a scattering cloud layer with a reasonably well-defined upper boundary.

Far-infrared spectral observations of Venus, Mars, and Jupiter

Spectra of Venus, Mars, and Jupiter between 45 and 115 μm have been obtained at a resolving power of ∼10, observing from the NASA Lear Jet at an altitude of 13.7 km. The results are calibrated with lunar observations, and show Mars and Venus to have relatively constant brightness temperatures over this wavelength region, with Venus appearing somewhat warmer at longer wavelengths. The brightness temperature of Jupiter decreases slightly toward longer wavelengths.

Scattering in the Atmosphere of Venus. I. Line profiles and curves of growth for isotropic scattering

We have computed line profiles and curves of growth for both reflected and transmitted radiation for typical lines in CO 2 bands (in the photographic infrared) which occur in the spectrum of Venus. In our model the pressure variation with altitude was considered and the base of the cloud deck was set at the 2 bar level. The temperature was held constant at 250K and a Voigt profile was used for the lineshape. We also assumed that the scale height of the cloud particles was equal to the scale height of the gas. The calculations were made for four values of the scattering optical thickness ( τ c = 0.1, 1.0, 10, and 100) using a continuum single scattering albedo ω c = 0.9975 (which gives a Bond albedo of 0.896 for τ c = 100, the value observed for Venus at these wavelengths). Curves of growth are also presented for reflected radiation which has been averaged over the visible disk for three values of the Venus phase angle (0, 86, and 166°).

Venus: Microwave Detection of Carbon Monoxide

The 115-gigahertz microwave line of carbon monoxide has been detected in the spectrum of Venus. The measurement proves that the carbon monoxide mixing ratio increases above an altitude of 85 kilometers in the Venus stratosphere and provides quantitative information on carbon monoxide in the altitude region from 80 to 110 kilometers. This altitude region is well above that which has been previously sensed.

Forbidden Ca ii in the Sun unmasked by way of Venus

Eleven high-dispersion spectra of Venus, taken with blue Doppler shifts have enabled us to unmask the 7323.88 A forbidden line of Ca ii from terrestrial absorption. We obtain an equivalent width of 7.4±0.4 mA for this line in integrated sunlight. Our value of W λ is smaller than previous values and much more accurate. The HSRA solar model gives a solar calcium abundance of A Ca = 6.21.

Sulfuric acid cloud interpretation of the infrared spectrum of Venus

view Abstract Citations (4) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Sulfuric acid cloud interpretation of the infrared spectrum of Venus. Martonchik, J. V. Abstract Sulfuric acid single-cloud models are compared with the Venus spectrum in the 8-14 micron region. The results indicate that a cloud composed of a 75 percent H2SO4 solution and with a particle density of 100 per cu cm is in good agreement with observations. In addition to explaining the 11.2 micron absorption, this model also predicts an absorption feature at 16.7 microns which should be detectable if the observation is made from an aircraft. Publication: The Astrophysical Journal Pub Date: October 1974 DOI: 10.1086/153185 Bibcode: 1974ApJ...193..495M Keywords: Atmospheric Models; Infrared Spectra; Sulfuric Acid; Venus Clouds; Absorption Spectra; Astronomical Models; Astronomical Spectroscopy; Carbon Dioxide; Cloud Physics; Particle Density (Concentration); Lunar and Planetary Exploration full text sources ADS |

Atomic chlorine on Venus

The possible presence of atomic chlorine in the upper atmosphere of Venus is examined. It is suggested that a Cl abundance as low as 2 ppm will be readily detectable in far ultraviolet via 1351.7 and 1335.7 Å emissions of neutral Cl atoms. These transitions can be resonantly excited by the bright solar emission line of C+, at 1335.7 Å. It is particularly interesting to investigate atomic chlorine since the bright 1356 Å emission feature which was reported by Rottman and Moos (1973) in the Venus spectra could not be explained without requiring high concentrations of atomic oxygen. From these data, a spectroscopic upper limit of 10−4 is deduced for the mixing ratio of Cl atoms at 125 km altitude. Although we cannot justify such a large mixing ratio, it may not be unreasonable considering the uncertainties in the present understanding of chlorine photochemistry on Venus.

Water vapor in Venus determined by airborne observations of the 8200 Å band

The region of the 8200 Å Band of H 2O 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 H 2O 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.

Comparison of the far ultraviolet spectra of Venus and Mars

Both Venus and Mars have largely CO2 atmospheres and as a result should be similar above the turbopause. Thus it is of interest to compare the far ultraviolet spectra of the two planets, both for similarities and for differences. A comparison between the Mariner 9 ultraviolet spectra of Mars and a spectrum of the total disk of Venus obtained from a sounding rocket is described. Data in the 1240- to 1800-A were used. Both the absolute and the relative intensities were compared.

Numerical Modelling of the Reflection Spectrum of Venus in the Visual and Near Infrared Ranges

The influence of a dense molecular atmosphere under a cloud layer on spectral albedo of a planet is investigated. The lengths of paths of protons in the clouds are calculated. Experimental spectral transmission functions were used to calculate gas absorption. The results are compared with experimental data.

Water Vapor in Venus Determined by Airborne Observations of the 8200 Å Band

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.These results establish that the average value over the entire disk is quite low but allows that locally larger values may exist as reported by Barker. A more complete description of this work appeared in Icarus21 (1974), 213.

Infrared Spectra of Venus

A historical account of observations of Venus and their interpretation is given. The major constituent of the atmosphere on Venus (CO2) was detected spectroscopically forty years ago, and minor constituents (CO, HF, HCl) have been found more recently. The infrared spectra also provide a means of studying the motions of her cloudy atmosphere. The composition of the clouds has been sought in the reflection spectrum of Venus, and some of the evidence for their nature is discussed.