Venus: a contrast in evolution to Earth

Of the planets, Venus and Earth are by far the most similar in primary properties, yet they differ markedly in secondary properties. A great impact into Earth is believed to have created its moon and removed its atmosphere; the lack of such an impact into Venus apparently led to a greatly differing atmospheric evolution. The lack of an ocean on Venus prevents the recycling of volatiles and inhibits subduction, so that its crust is probably more voluminous than Earth's, although distorted and quite variable in thickness. Venus's upper mantle appears to be depleted in both volatiles and energy sources because, in addition to the lack of volatile recycling, melts of mantle rocks are more dense than their solid matrix at pressures above 8 gigapascals and hence sink if they occur at depths below 250 kilometers. Appreciable energy sources persist at great depths to sustain the few great mountain complexes. The greatest current problem is reconciling the likelihood of a voluminous crust with indications of considerable strength at shallow depths of 20 to 100 kilometers.     

Structure of the Atmosphere of Venus up to 110 Kilometers: Preliminary Results from the Four Pioneer Venus Entry Probes

The four Pioneer Venus entry probes transmitted data of good quality on the structure of the atmosphere below the clouds. Contrast of the structure below an altitude of 50 kilometers at four widely separated locations was found to be no more than a few degrees Kelvin, with slightly warmer temperatures at 30 degrees south latitude than at 5 degrees or 60 degrees north. The atmosphere was stably stratified above 15 or 20 kilometers, indicating that the near-adiabatic state is maintained by the general circulation. The profiles move from near-adiabatic toward radiative equilibrium at altitudes above 40 kilometers. There appears to be a region of vertical convection above the dense cloud deck, which lies at 47.5 to 49 kilometers and at temperature levels near 360 K. The atmosphere is nearly isothermal around 100 kilometers (175 to 180 K) and appears to exhibit a sizable temperature wave between 60 and 70 kilometers. This is where the 4-day wind is believed to occur. The temperature wave may be related to some of the wavelike phenomena seen in Mariner 10 ultraviolet photographs.     

Venus clouds: a dirty hydrochloric Acid model

The spectral and polarization data for Venus are consistent with micrometer-sized aerosol cloud particles of hydrochloric acid with soluble and insoluble iron compounds, whose source could be volcanic or crustal dust. The yellow color of the clouds could be due to absorption bands in the near ultraviolet involving ferric iron and chlorine complexes. The ultraviolet features could arise from variations in the concentrations of iron and hydrochloric acid in the cloud particles.     

Venus: absence of a phase effect at a 2-centimeter wavelength

Observations of Venus made during 1967 and 1968 at a frequency of 15.4 gigahertz set an upper limits of 5 percent for the variation of brightness temperature with phase. This negative result appears to contradict earlier detections of a phase effect. By comparison with Virg A (3C 274), which has an assumed flux density of 29 x 10(-26) watt per square meter per hertz, the brightness temperature of Venus at this frequency is 485 + 60, -40 degrees K (mean error).     

Aboriginal Drained-Field Cultivation in the Americas: Pre-Columbian reclamation of wet lands was widespread in the savannas and highlands of Latin America

The three main types of land reclamation in aboriginal America were irrigation, terracing, and drainage. Of these, drainage techniques have received the least attention, probably because they are no longer important and because the remnants are not conspicuous. Nevertheless, drained-field cultivation was widespread and was practiced in varied environments, including high-land basins, tropical savannas, and temperate flood plains. Sites ranged from seasonally waterlogged or flooded areas to permanent lakes. Ridging, mounding, and ditching were emphasized, rather than diking. Tools were simple, crops varied, and fertilization was accomplished mainly by mulching.     

Thermal Structure and Major Ion Composition of the Venus Ionosphere: First RPA Results from Venus Orbiter

Thermal plasma quantities measured by, the retarding potential analyzer (RPA) are, together with companion Pioneer Venus measurements, the first in situ measurements of the Venus ionosphere. High ionospheric ion and electron temperatures imply significant solar wind heating of the ionosphere. Comparison of the measured altitude profiles of the dominant ions with an initial modlel indicates that the ionosphere is close to diffusive equilibrium. The ionopause height was observed to vary from 400 to 1000 kilometers in early orbits. The ionospheric particle pressure at the ionopause is apparently balanced at a solar zenith angle of about 70 degrees by the magnetic field pressure with little contribution from energetic solar wind particles. The measured ratio of ionospheric scale height to ionopause radius is consistent with that inferred from previously measured bow shock positions.     

Venus: composition and structure of the visible clouds

It is proposed that the visible cloud deck on Venus is composed of droplets of sulfuric acid. These are formed by the very rapid photooxidation of carbonyl sulfide in the upper atmosphere. The clouds are best described as an extensive haze since the predicted particulate scale height probably exceeds the gas scale height within the layer. The predicted mixing ratio for water is 10(-6) (lower limit), and for both carbonyl sulfide and sulfur dioxide it is 10(-7) (upper limit); these are in good agreement with observations. Gaps in the layer are not possible unless the planetary scale dynamics produce cloud turnover times of less than a few days. Under these conditions the water mixing ratio could approach 10(-4) and the formation of a thin hydrochloric acid haze at high altitude above the main cloud is possible.     

Venus: radar determination of gravity potential

We describe a method for the determination of the gravity potential of Venus from multiple-frequency radar measurements. The method is based on the strong frequency dependence of the absorption of radio waves in Venus' atmosphere. Comparison of the differing radar reflection intensities at several frequencies yields the height of the surface relative to a reference pressure contour; combination with measurements of round-trip echo delays allows the pressure, and hence the gravity potential contour, to be mapped relative to the mean planet radius. Since calibration data from other frequencies are unavailable, the absorption-sensitive Haystack Observatory data have been analyzed under the assumption of uniform surface reflectivity to yield a gravity equipotential contour for the equatorial region and a tentative upper bound of 6 x 10(-4) on the fractional difference of Venus' principal equatorial moments of inertia. The minima in the equipotential contours appear to be associated with topographic minima.     

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.     

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.     

Venus: mapping the surface reflectivity by radar interferometry

The surface reflectivity of Venus obtained by radar interferometry at a wavelength of 3.8 centimeters has been mapped for a region extending approximately from -80 degrees to 0 degrees in longitude (Carpenter's definition) and from -50 degrees to +40 degrees in latitude. The map is free from the twofold range-Doppler ambiguity because the interferometer fringe pattern makes possible the separation of two points of equal range and Doppler shift. The map presents many new features and clearly delineates features already observed. Most notably, the map shows large circular regions of significantly lower reflectivity than their surroundinigs.     

Venus: detailed mapping of maxwell montes region

From October 1983 to July 1984, the north hemisphere of Venus, from latitude 30 degrees to latitude 90 degrees , was mapped by means of the radar imagers and altimeters of the spacecraft Venera 15 and Venera 16. This report presents the results of the radar mapping of the Maxwell Montes region, one of the most interesting features of Venus' surface. A radar mosaic map and contour map have been compiled.     

Venus: uniformity of clouds, and photography

Photographs of Earth at a resolution of about 600 kilometers were compared to pictures of Venus taken from Earth at about the same resolution . Under these conditions Earth appear very heavily covered by clouds. Since details on the surface of Earth can be recorded from Earth orbit, it may be possible to phiotograph protions of the surface of Venus, through openings in the clouds, from an orbiting satellite.     

Chemistry and Petrology of Venus: Preliminary Deductions

Recent measuremnents of the temperature of Venus suggest that a chemical interaction between the atmosphere and lithosphere may occur: the possible consequences of such interaction are examined. Results indicate that metallic iron, free carbon, and magnesium carbonates should not occur on the surface of Venus. Calcium carbonate, iron oxides and certain hydrous silicates may be present, but other hydrous silicates seem to be excluded. The effects of the physicochemical conditions on rock types and the various planetary processes are discussed.     

Venus: A Map of Its Brightness Temperature

The 200-inch Hale telescope has been used to make high-resolution maps of the brightness temperature of Venus at wavelengths 8 to 14 microns. Resolution of about 1/30 of the disk reveals a general symmetry about the plane of the orbit, no daynight temperature effects, and a transient temperature anomaly in the southern hemisphere.     

Thermal Structure and Energy Influx to the Day-and Nightside Venus Ionosphere

Pioneer Venus in situ measurements made with the retarding potential analyzer reveal strong variations in the nightside ionospheric plasma density from location to location in some orbits and from orbit to orbit. The ionopause is evident at night as a relatively abrupt decrease in the thermal plasma concentration from a few hundred to ten or fewer ions per cubic centimeter. The nightside ion and electron temperatures above an altitude of 250 kilometers, within the ionosphere and away from the terminator, are comparable in magnitude and have a value at the ionopause of approximately 8000 K. The electron temperature increases from a few tens of thousands of degrees Kelvin just outside the ionopause to several hundreds of thoussands of degrees Kelvin further into the shocked solar wind. The coldest ion temperatures measured at an altitude of about 145 kilometers are 140 to 150 K and are still evidently above the neutral temperature. Preliminary day-and nightside model ion and electron temperature height profiles are compared with measured profiles. To raise the model ion temperature to the measured ion temperature on both day-and nightsides, it was necessary to include an ion energy source of the order of 4 x 10(-3) erg per square centimeter per second, presumably Joule heating. The heat flux through the electron gas from the solar wind into the neutral atmosphere averaged over day and night may be as large as 0.05 erg per square centimeter per second. Integrated over the planet surface, this heat flux represents one-tenth of the solar wind energy expended in drag on the sunward ionopause hemisphere.