M.Ya. Marov

Models of the structure of the atmosphere of Venus from the surface to 100 kilometers altitude

From a critical comparison and synthesis of data from the four Pioneer Venus Probes, the Pioneer Venus Orbiter, and the Venera 10, 12, and 13 landers, models of the lower and middle atmosphere of Venus are derived. The models are consistent with the data sets within the measurement uncertainties and established variability of the atmosphere. The models represent the observed variations of state properties with latitude, and preserve the observed static stability. The rationale and the approach used to derive the models are discussed, and the remaining uncertainties are estimated.

Venus: A perspective at the beginning of planetary exploration☆

Abstract In situ measurements of the Venus atmosphere, made by the entry probes Venera 4, 5, 6, and 7, and data from the Mariner 5 flyby, have provided essentially new and reliable information and have powerfully contributed to our understanding of the nearest planet. The abundances of the principal atmospheric constituents and the temperature and pressure profiles down to the Venus surface were obtained for the first time. It was shown that the atmosphere is composed primarily of CO2 and that N2 (if any) and H2O are relatively minor admixtures. In the region of the Venera 7 landing, the temperature and pressure at the Venus surface were established as equal to 747 ± 20°K and 90 ± 15 kgcm−2. Space vehicles have also provided limited but quite important information on the physical properties of the Venus upper atmosphere and ionosphere, and on the interaction of the planet with the interplanetary environment. The main characteristics of the Venus atmosphere are discussed here with emphasis on the Venera results, including instrumentation, data processing, and altitude profiles. As a result of both direct measurements and analysis of refractivity and microwave data, a thermodynamic gas state in the Venus troposphere was evaluated that corresponds as a whole to adiabatic equilibrium. Nevertheless, analysis of the Venus troposphere reveals some peculiarities in the height profiles that apparently are not explained in terms of an adiabatic lapse rate in pure CO2 for all levels where measurements were performed. Minor ingredients evaporated into the atmosphere from the hot surface could influence the thermodynamic gas state. While the data on the nature of the clouds are rather scarce, some problems on their structure and composition seem worthwhile to discuss, and in so doing we emphasize the possibilities of ice crystals and/or H2O solutions and mixtures. A multilayered structure for the Venus clouds, composed of different volatiles at several levels, is considered to be plausible as well. The mechanism of radiative and convective heat transfer in the Venus lower atmosphere and the greenhouse and deep circulation models are discussed. A model of the Venus atmosphere up to several hundred kilometers above the surface, based on results of Venera and Mariner 5 measurements and data from ground-based optical and radio observations, is developed. Progress is radar astronomy allows a more precise understanding of the relief of the Venus surface, and Venera 7 uncovered the very first information on the strength of the surface material. Some evidence on the origin and evolution of Venus as a planet, as well as some prospective problems for further study, are also briefly discussed.

Particulate matter in the Venus atmosphere

Abstract We present a summary of the data currently available (June 1984) describing the planet-enshrouding particulate matter in the Venus atmosphere. A description and discussion of the state of knowledge of the Venus clouds and hazes precedes the tables and plots. The tabular material includes a precis of upper haze and cloud-top properties, parameters for model-size distributions for particles and particulate layers, and columnar masses and mass loadings. The plots are of experimental and derived quantities and include: (1) altitude dependences of volumetric scattering cross sections, size mode number densities, mass loadings, and optical depths, (2) wavelength dependences of asymmetry parameters and optical depths, and (3) latitude and longitude dependence of cloud top properties.

Preliminary results on the Venus atmosphere from the Venera 8 descent module

Abstract The Venera 8 descent module measured pressure, temperature, winds and illumination as a function of altitude in its landing on July 22, 1972, just beyond the terminator in the illuminated hemisphere of Venus. The surface temperature and pressure is 741 ± 7°K and 93 ± 1.5kgcm −2 , consistent with early Venera observations and showing either no diurnal variation or insignificant diurnal variation in temperature and pressure in the vicinity of the morning terminator. The atmosphere is adiabatic down to the surface. The horizontal wind speed is low near the surface, about 35m/sec between 20 and 40km altitude, and increasing rapidly above 48km altitude to 100–140m/sec, consistent with the 4-day retrograde rotation of the ultraviolet clouds. The illumination at the center of the day hemisphere of Venus is calculated to be about 1% of the solar flux at the top of the atmosphere, consistent with greenhouse models and high enough to permit photography of the Venus surface by future missions. The attenuation below 35km altitude is explained by Rayleigh scattering with no atmospheric aerosols; above 35km there must be substantial extinction of incident light.

Phobos-Grunt: Russian sample return mission

Abstract As an important milestone in the exploration of Mars and small bodies, a new generation space vehicle “Phobos-Grunt” is planned to be launched by the Russian Aviation and Space Agency. The project is optimized around a Phobos sample return mission and follow up missions targeted to study some main asteroid belt bodies, NEOs and short period comets. The principal constraint is use of the “Soyuz-Fregat” rather than the “Proton” launcher to accomplish these challenging goals. The vehicle design incorporates innovative SEP technology involving electrojet engines that allowed us to increase significantly the missions energetic capabilities, as well as highly autonomous on-board systems. Basic criteria underlining the “Phobos-Grunt” mission scenario, scientific objectives and rationale including Mars observations during the vehicles insertion into Mars orbit and Phobos approach maneuvers, are discussed and an opportunity for international cooperation is suggested.

The structure and microphysical properties of the Venus clouds: Venera 9, 10, and 11 data

Data processing and interpretation of the nephelometer measurements made in the Venus atmosphere aboard the Venera 9, 10 and 11 landers in the sunlit hemisphere near the equator are discussed. These results were used to obtain the aerosol distribution and its microphysical properties from 62 km to the surface. The main aerosol content is found in the altitude range between 62 km (where measurements began) and 48 km, the location of the cloud region. Three prominent layers labeled as I (between 62 and 57 km), II (between 57 and 51 km) and III (between 51 and 48 km), each with different particle characteristics are discovered within the clouds. The measured light-scattering patterns can be intrepreted as having been produced by particles with effective radii from 1 to 2 μm depending on height and indices of refractivity from 1.45 in layer I to 1.42 in layer III. These values do not contradict the idea that the droplets are made of sulfuric acid. In layers II and III the particle size distribution is at least bimodal rather than uni-modal. The index of refraction is found to decrease to 1.33 in the lower part of layer II, suggesting a predominant abundance of larger particles of different chemical origin, and chlorine compounds are assumed to be relevant to this effect. In the entire heightrange of the Venera 9–11 craft descents, the clouds are rather rarefied and are characterized by a mean volume scattering coefficient σ ∼ 2 × 10−5 cm−1 that corresponds to the mean meteorological range of visibility of about 2 km. The average mass content of condensate is estimated to be equal to 4 × 10−9 g/cm3, and the total optical depth of clouds to τ ∼ 35. Near the bottom of layer III clouds are strongly variable. In the subcloud atmosphere a haze was observed between 48 and 32 km; that haze is mainly made of submicron particles, reff ∼ 0.1μm. The atmosphere below that is totally transparent but separate (sometimes possibly disappearing) layers may be present up to a height of 8 km above the surface. A model of this region with a very low particle density (N ≲ 2–3 cm−3) strongly refractive large particles (reff ≳ 2.5 μm; 1.7 < n < 2.0) provided satisfactory agreement. The optical depth of aerosol in the atmosphere below the subcloud haze does not exceed 2.5.

Data on dynamics of the subcloud Venus atmosphere from Venera Spaceprobe measurements

Abstract This paper presents the principal results of wind velocity and turbulence measurements in the Venus atmosphere during the Venera flights. Based on one-way Doppler measurements wind estimations were obtained as a difference of the measured and computed descent velocity values. The computation of free parachute descent velocity was performed by an independent method that utilized aerodynamics of the spaceprobes and the pressure-temperature measurements of the Venus atmosphere. Entry point location, dynamics of the parachute-spaceprobe system as well as frequency instability of the on-board crystal oscillators are basic factors which influenced the accuracy of wind and turbulence estimations. Venera 4 measured a strong wind (up to 40–50 m sec −1 ) and turbulence at 0.7–4 bar levels (40–50km altitude); within the measurement errors neither wind nor turbulence were found at altitudes lower than 40 km. Venera 5 and Venera 6 Doppler data indicated very smooth velocity changes during the whole descent without noticeable signs of turbulence. Venera 7 measured a zonal wind component; values 5–14 m sec −1 were obtained at 38–53 km altitudes; below 38 km the wind velocity was zero. Estimation of wind velocity near the planet surface (0–3.5 km) leads to value of 0–2.5 m sec −1 . Based on an analysis of the apparatus construction characteristics and the radio signal variation during impact upon the Venus surface, values of 2–80 kg cm −2 were obtained for the bearing strength of the soil.

Stochastic models of hot planetary and satellite coronas: Total water loss in the Martian atmosphere

Estimates of the total thermal and nonthermal losses of hydrogen and the total nonthermal loss of oxygen from the atmosphere of Mars are discussed, and their ratio is analyzed. It is shown that an H to O ratio of 2:1 has not been achieved in any of the current models of various authors. The closest ratio, H:O = 4:1, has been obtained by Krestyanikova and Shematovich (2006) in the model of formation of a hot oxygen corona.

Investigations of Mars from the Soviet automatic stations Mars 2 and 3

Abstract Preliminary results from the Mars 2 and 3 orbiters and landers are presented, including descriptions of the spacecraft and their operation; orbital elements; landing sequencing; and scientific results on the distribution of temperature, water vapor, dielectric constant, elevation, and photometric properties over the surface of Mars. Further results are given on ultraviolet emission, interplanetary and circum-Martian plasmas, high altitude ultraviolet clouds, ionospheric electron densities, and a zone of thermalized ions. A surface equatorial magnetic field strength of about 60γ is deduced. Orbital photography implies a value of the optical oblateness close to the dynamical value. Interesting twilight phenomena have been uncovered.

Fundamentals of the mechanics of heterogeneous media in the circumsolar protoplanetary cloud: The effects of solid particles on disk turbulence

We formulate a complete system of equations of two-phase multicomponent mechanics including the relative motion of the phases, coagulation processes, phase transitions, chemical reactions, and radiation in terms of the problem of reconstructing the evolution of the protoplanetary gas-dust cloud that surrounded the proto-Sun at an early stage of its existence. These equations are intended for schematized formulations and numerical solutions of special model problems on mutually consistent modeling of the structure, dynamics, thermal regime, and chemical composition of the circumsolar disk at various stages of its evolution, in particular, the developed turbulent motions of a coagulating gas suspension that lead to the formation of a dust subdisk, its gravitational instability, and the subsequent formation and growth of planetesimals. To phenomenologically describe the turbulent flows of disk material, we perform a Favre probability-theoretical averaging of the stochastic equations of heterogeneous mechanics and derive defining relations for the turbulent flows of interphase diffusion and heat as well as for the “relative” and Reynolds stress tensors needed to close the equations of mean motion. Particular attention is given to studying the influence of the inertial effects of dust particles on the properties of turbulence in the disk, in particular, on the additional generation of turbulent energy by large particles near the equatorial plane of the proto-Sun. We develop a semiempirical method of modeling the coefficient of turbulent viscosity in a two-phase disk medium by taking into account the inverse effects of the transfer of a dispersed phase (or heat) on the growth of turbulence to model the vertically nonuniform thermohydrodynamic structure of the subdisk and its atmosphere. We analyze the possible “regime of limiting saturation” of the subdisk atmosphere by fine dust particles that is responsible for the intensification of various coagulation mechanisms in a turbulized medium. For steady motion when solid particles settle to the midplane of the disk under gravity, we analyze the parametric method of moments for solving the Smoluchowski integro-differential coagulation equation for the particle size distribution function. This method is based on the fact that the sought-for distribution function a priori belongs to a certain parametric class of distributions.