Clouds of venus: evidence for their nature

The linear polarization of sunlight multiply scattered by the atmosphere, and cloud particles of Venus has been computed and compared with observations over the wavelength range from the ultraviolet to the infrared region. The following properties of the visible cloud layer are derived: the refractive index of the cloud particles is 1.45 +/- 0.02 at a wavelength of 0.55 micron, and there is an indication of a slight decrease in the value from the ultraviolet to the near-infrared region; the mean particle radius is very near 1 micron, and most of the particles are spherical; the cloud layer occurs high in the atmosphere where the pressure is about 50 millibars (equivalent to an altitude of approximately 20 kilometers on the earth). The results for the index of refraction eliminate the possibility that the visible clouds are composed of pure water or ice.     

Styles of volcanism on venus: new arecibo high resolution radar data

Arecibo high-resolution (1.5 to 2 km) radar data of Venus for the area extending from Beta Regio to western Eisila Regio provide strong evidence that the mountains in Beta and Eisila Regiones and plains in and adjacent to Guinevere Planitia are of volcanic origin. Recognized styles of volcanism include large volcanic edifices on the Beta and Eisila rises related to regional structural trends, plains with multiple source vents and a mottled appearance due to the ponding of volcanic flows, and plains with bright features surrounded by extensive quasi-circular radar-dark halos. The high density of volcanic vents in the plains suggests that heat loss by abundant and widely distributed plains volcanism may be more significant than previously recognized. The low density of impact craters greater than 15 km in diameter in this region compared to the average density for the higher northern latitudes suggests that the plains have a younger age.     

Io: evidence for silicate volcanism in 1986

Infrared observations of Io during the 1986 apparition of Jupiter indicate that a large eruptive event occurred on the leading side of Io on 7 August 1986, Universal Time. Measurements made at 4.8, 8.7, and 20 micrometers suggest that the source of the event was about 15 kilometers in radius with a model temperature of approximately 900 Kelvin. Together with previously reported events, these measurements indicate that high-temperature volcanic activity on the leading side of Io may be more frequent than previously thought. The inferred temperature is significantly above the boiling point of sulfur in a vacuum(715 Kelvin) and thus constitutes strong evidence for active silicate volcanism on the surface of Io.     

Tectonics and volcanism of eastern aphrodite terra, venus: no subduction, no spreading

Eastern Aphrodite Terra, a deformed region with high topographic relief on Venus, has been interpreted as analogous to a terrestrial extensional or convergent plate boundary. However, analysis of geological and structural relations indicates that the tectonics of eastern Aphrodite Terra is dominated by blistering of the crust by magma diapirs. The findings imply that, within this region, vertical tectonism dominates over horizontal tectonism and, consequently, that this region is neither a divergent nor a convergent plate boundary.     

Surface of venus: evidence of diverse landforms from radar observations

Recent radar images of the surface of Venus reveal a complex and varied terrain. By applying a set of simplifying assumptions about the nature of the surfaces returning the radar signal, it is possible to make a number of plausible interpretations. In one region on Venus, several circular features have the gross morphology of degraded impact craters. If they are indeed of impact origin, these features suggest that there exist on Venus areas which are ancient and where erosion or resurfacing has not been as intense or as pervasive as on the earth. In other regions there are intriguing features that may evidence active internal processes. One is a large trough-like depression (0 degrees , 76 degrees W; measuring 1400 by 150 by 2 kilometers) planimetrically suggestive of both the Valles Marineris on Mars and the East African Rift on the earth. Another feature, about 250 kilometers in diameter and of positive relief, includes an 80-kilometer-diameter circular depression at its summit, suggestive of a large volcanic construct. A third region, near 0 degrees , 10 degrees E, contains roughly parallel ranges of mountains separated by valley-like features, with relief varying from small isolated hills several hundred meters high to low ranges on the order of 1000 meters to large mountains approaching 2 kilometers in height. If Venus has a mobile crust similar to the earth's, these mountains may have been produced by compressional tectonics. These interpretations of the radar data indicate that Venus has been a geologically active planet which has developed diverse landforms and therefore is an exciting candidate for future exploration.     

Helium on venus: implications for uranium and thorium

Helium is removed at an average rate of 10(6) atoms per square centimeter per second from Venus's atmosphere by the solar wind following ionization above the plasmapause. The surface source of helium-4 on Venus is similar to that on Earth, suggesting comparable abundances of crustal uranium and thorium.     

Sulfur dioxide emissions from power plants: their effect on air quality

A modeling study of atmospheric diffusion indicates that emission from power plants contributed only a modest percentage of the yearly average concentration of sulfur dioxide at ground level in the most polluted areas of Cook County, Illinois, during 1968.     

Carbon dioxide exchange between air and seawater: no evidence for rate catalysis

It has been suggested that enzymatic catalysis plays a major role in regulating the mass transport of carbon dioxide from the atmosphere into the oceans. Evidence for this mechanism was not found in a series of gas exchange experiments in which the gas transfer rate coefficients for samples obtained from various natural seawaters, with and without the addition of carbonic anhydrase, were compared with those from artificial seawater. Wind-induced turbulence appears to be the major factor controlling the ocean's response to anthropogenic increases in atmospheric carbon dioxide.     

Thyrotropin-releasing hormone: evidence for thyroid response to intravenous injection in man

Administration of thyrotropin-releasing hormone to normal subjects causes a prompt rise in plasma thyrotropin concentration, followed by a significant increase in circulating plasma triiodothyronine. These observations may prove to be of value in simultaneously assessing the ability of the pituitary and thyroid glands to respond to their trophic hormones.     

Increasing atmospheric carbon dioxide: tree ring evidence for growth enhancement in natural vegetation

A response of plant growth to increased atmospheric carbon dioxide, which has been anticipated from laboratory data, may now have been detected in the annual rings of subalpine conifers growing in the western United States. Experimental evidence shows that carbon dioxide can be an important limiting factor in the growth of plants in this high-altitude environment. The greatly increased tree growth rates observed since the mid-l9th century exceed those expected from climatic trends but are consistent in magnitude with global trends in carbon dioxide, especially in recent decades. If correctly interpreted, these findings have important implications for climate studies involving tree ring observations and for models of the global carbon dioxide budget.     

Magmatic vapor source for sulfur dioxide released during volcanic eruptions: evidence from mount pinatubo

Sulfur dioxide (SO(2)) released by the explosive eruption of Mount Pinatubo on 15 June 1991 had an impact on climate and stratospheric ozone. The total mass of SO(2) released was much greater than the amount dissolved in the magma before the eruption, and thus an additional source for the excess SO(2) is required. Infrared spectroscopic analyses of dissolved water and carbon dioxide in glass inclusions from quartz phenocrysts demonstrate that before eruption the magma contained a separate, SO(2)-bearing vapor phase. Data for gas emissions from other volcanoes in subduction-related arcs suggest that preeruptive magmatic vapor is a major source of the SO(2) that is released during many volcanic eruptions.     

Moving flame experiment with liquid mercury: possible implications for the venus atmosphere

A bunsen flame rotated under a cylindrical annulus filled with liquid mercury forces the liquid mercury to rotate in a direction counter to that of the rotating flame. The rate of rotation of the liquid is several times greater than that of the flame. This observation may provide an explanation for the high velocities of apparent cloud formations in the upper atmosphere of Venus.     

Water sources for subduction zone volcanism: new experimental constraints

Despite its acknowledged importance, the role of water in the genesis of subduction zone volcanism is poorly understood. Amphibole dehydration in subducting oceanic crust at a single pressure is assumed to generate the water required for melting, but experimental constraints on the reaction are limited, and little attention has been paid to reactions involving other hydrous minerals. Experiments on an oceanic basalt at pressure-temperature conditions relevant to subducting slabs demonstrate that amphibole dehydration is spread over a depth interval of at least 20 kilometers. Reactions involving other hydrous minerals, including mica, epidote, chloritoid, and lawsonite, also release water over a wide depth interval, and in some subduction zones these phases may transport water to deep levels in the mantle.     

Impact crater densities on volcanoes and coronae on venus: implications for volcanic resurfacing

The density of impact craters on large volcanoes on Venus is half the average crater density for the planet. The crater density on some classes of coronae is not significantly different from the global average density, but coronae with extensive associated volcanic deposits have lower crater densities. These results are inconsistent with both single-age and steady-state models for global resurfacing and suggest that volcanoes and coronae with associated volcanism have been active on Venus over the last 500 million years.     

Solar cycle variation of exospheric temperatures Mars and venus: a prediction for mariner 6 and 7

Calculations have been made to determine the effects of variations in the extreme ultraviolet solar radiation on the upper atmospheres of mars and Venus. The results indicate that the exospheric temperature from 300 degrees K to 600 degrees K during the solar cycle, with a corresponding range on Venus of 450 degrees K to 850 degrees K. At the present time, the temperature of the Martain exosphere should be approximately 500 degrees K.     

Cumulate xenolith in oahu, hawaii: implications for deep magma chambers and hawaiian volcanism

The maximum depth at which large (>1000 km(3)) terrestrial mafic magma chambers can form has generally been thought to be the Moho, which occurs at a mean depth of about 35 kilometers beneath the continents and 8 kilometers beneath ocean basins. However, the presence of layers of cumulus magnesium-rich spinel and olivine and intercumulus garnet in an unusual mantle xenolith from Oahu, Hawaii, suggests that this rock is a fragment of a large magma chamber that formed at a depth of about 90 kilometers; Hawaiian shield-building magmas may pond and fractionate in such magma chambers before continuing their ascent. This depth is at or near the base of the 90-million-year-old lithosphere beneath Oahu; thus, rejuvenated stage alkalic magmas containing mantle xenoliths evidently also originate below the lithosphere.     

Perineurium: evidence for contractile elements

Electron-microscopic study of mouse sciatic nerve reveals that perineurial cells contain filaments and associated opaque regions similar to those observed in smooth muscle. This finding is consistent with obsevations Which suggest that nerve might have a contractile property. In addition to their function in maintaining the connective tissue stroma of perineurium, as well as being a selective diffusion barrier, perineurial cells may serve the nerve in a contractile capacity.     

Pluto: evidence for methane frost

Infrared photometry (1.2 to 2.2 micrometers) of Pluto provides evidence for frozen methane on the surface of the planet. This appears to be the first observational indication of this ice in the solar system. Its presence on Pluto suggests that the planet's albedo (reflectance) may be >/= 0.4 and that its diameter may be less than that of the moon.     

Thyrocalcitonin: evidence for physiological function

A calcium salt given by stomach tube in modest amounts, such as might be ingested in a normal meal, produced hypercalcemia in acutely thyroidectomized fasted rats, whereas in rats with intact thyroid glands the same dose of calcium had little or no detectable effect, presumably because of release of thyrocalcitonin. Thyrocalcitonin apparently protects against hypercalcemia during feeding after deprivation.