Some objects seem to wander around in the night sky relative to many of the visual points of light. At least one occasionally is present in the early morning before sunrise as the Morning Star and after sunset as the Evening Star, the planet Venus.
In visual astronomy almost no variation or detail can be seen in the clouds. The surface is obscured by a thick blanket of clouds. Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in visible light. It has thick clouds of sulfur dioxide. There are lower and middle cloud layers. The thick clouds consisting mainly of sulfur dioxide and sulfuric acid droplets. These clouds reflect and scatter about 90% of the sunlight that falls on them back into space, and prevent visual observation of the Venusian surface. The permanent cloud cover means that although Venus is closer than Earth to the Sun, the Venusian surface is not as well lit.
Strong 300 km/h winds at the cloud tops circle the planet about every four to five earth days. Venusian winds move at up to 60 times the speed of the planet's rotation, while Earth's fastest winds are only 10% to 20% rotation speed.
"Average cloud-top wind speeds on Venus rose 33 percent between 2006 and 2012, jumping from 186 mph (300 km/h) to 249 mph (400 km/h), observations by Europe's Venus Express orbiter show."
"This is an enormous increase in the already high wind speeds known in the atmosphere, ... Such a large variation has never before been observed on Venus, and we do not yet understand why this occurred."
The wind speeds are determined "by studying images captured by Venus Express between [50° N and S latitude, and tracking] the movements of tens of thousands of feature in the cloud tops some [70 km] above the planet's surface."
"Our analysis of cloud motions at low latitudes in the southern hemisphere showed that over the six years of study the velocity of the winds changed by up 70 km/h over a time scale of 255 Earth days — slightly longer than a year on Venus".
"Sometimes clouds took 3.9 days to zip all the way around Venus, for example, while on other occasions the journey required 5.3 days."
"Although there is clear evidence that the average global wind speeds have increased, further investigations are needed in order to explain what drives the atmospheric circulation patterns that are responsible, and to explain the changes seen in localized areas on shorter timescales ... The atmospheric super-rotation of Venus is one of the great unexplained mysteries of the solar system ... These results add more mystery to it, as Venus Express continues to surprise us with its ongoing observations of this dynamic, changing planet."
"Venus has a super-rotating atmosphere that whips around the planet once every four Earth days; Venus itself takes 243 Earth days to complete one rotation."
The first ever X-ray image of Venus is shown at right. The "half crescent is due to the relative orientation of the Sun, Earth and Venus. The X-rays from Venus are produced by fluorescent radiation from oxygen and other atoms in the atmosphere between 120 and 140 kilometers above the surface of the planet. In contrast, the optical light from Venus is caused by the reflection from clouds 50 to 70 kilometers above the surface. Solar X-rays bombard the atmosphere of Venus, knock electrons out of the inner parts of atoms, and excite the atoms to a higher energy level. The atoms almost immediately return to their lower energy state with the emission of a fluorescent X-ray. A similar process involving ultraviolet light produces the visible light from fluorescent lamps."
When imaged in the ultraviolet on the right, Venus appears like a gas dwarf object rather than a rocky object.
The image on the lower right has been re-processed through the clear, blue, and UV filters of Mariner 10 from the image taken of Venus by Mariner 10 on May 5, 1974, to show greater detail.
On the left is an image of Venus in the ultraviolet by the Hubble Space Telescope.
Second down on the left is a closeup equatorial ultraviolet image from the Japanese space agency’s Akatsuki spacecraft during a close approach to Venus near peiapsis of about 400 km (250 mi) from Venus's surface. On 26 March 2016 Akatsuki's apoapsis was lowered to about 330,000 km (210,000 mi) and shortened its orbital period from 13 to 9 days.
When imaged in visible light (right at page top) Venus appears like a gas dwarf rather than a rocky body. The same image result occurs when it is viewed in the ultraviolet.
On the right is a composite "Venera 13 Lander image of the surface of Venus at 7.5 S, 303. E, east of Phoebe Regio. Venera 13 survived on the surface for 2 hours, 7 minutes, long enough to obtain 14 images on 1 March, 1982. This color 170 degree panorama was produced using dark blue, green and red filters and has a resolution of 4 to 5 min. Part of the spacecraft is at the bottom of the image. Flat rock slabs and soil are visible. The true color is difficult to judge because the Venerian atmosphere filters out blue light. The surface composition is similar to terrestrial basalt. On the ground in foreground is a camera lens cover."
Violet photographs of the planet Venus taken in 1927 “recorded two nebulous bright streaks, or bands, running ... approximately at right angles to the terminator” that may be from the upper atmosphere.
In 1959 "observations of the spectrum of the planet Venus, with spectrographs of low and high dispersion at the Georgetown College Observatory, show that a wide, continuous absorption band is present in the violet and near-ultraviolet."
The image at the top right is from the Galileo spacecraft solid state imaging system taken on February 14, 1990. The satellite was about 2.7 million km from the planet. The highpass violet filter (418 nm) has been applied to emphasize the smaller scale cloud features. This rendition has been colorized bluish to emphasize subtle contrasts in the cloud markings. The sulfuric acid clouds indicate considerable convective activity. The filamentary dark features are composed of several dark nodules, like beads on a string, each about 96 km across.
The image at right is from a "series of pictures [that show] four views of the planet Venus obtained by Galileo's Solid State Imaging System at ranges of 1.4 to 2 million miles as the spacecraft receded from Venus. The pictures [the first two] were taken about 4 and 5 days after closest approach; those ... were taken about 6 days out, 2 hours apart [of which the image at right is the last]. In these violet-light images, north is at the top and the evening terminator to the left. The cloud features high in the planet's atmosphere rotate from right to left, from the limb through the noon meridian toward the terminator, traveling all the way around the planet once every four days. The motion can be seen by comparing the last two pictures, taken two hours apart. The other views show entirely different faces of Venus. These photographs are part of the 'Venus global circulation' sequence planned by the imaging team."
Although shown in black and white, the image on the right was taken at 630 nm in the red.
"During the MESSENGER mission's second flyby of Venus, the Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS) acquired images through all of its 11 narrow-band color filters of the approaching planet. The surface of Venus is shrouded in clouds, and the WAC images returned from the encounter show this cloud covered view, as seen in a previously released image. However, by processing the WAC images and "stretching" the gray scale used to display the images, subtle differences in the clouds of Venus are revealed, as seen in the image here. This WAC image was taken through a narrow-band filter centered at 630 nanometers, and in this stretched image, global circulation patterns can be seen in the atmosphere of Venus."
"The Herzberg II system of O2 has been a known feature of Venus' nightglow since the Venera 9 and 10 orbiters detected its c(0)-X(v″) progression more than 3 decades ago."
"Spectroscopic observations of the differential Doppler shift in a CO2 absorption line on Venus show that the upper atmospheric wind near the equator appears to have both a retrograde motion of about -85 ± 10 m s-1 ... and ... a periodically varying component, with an amplitude of about 40 ± 14 m s-1 and a period of 4.3 ± 0.2 days."
At right is a false-color near-infrared image of the lower-level clouds on the night side of Venus, obtained by the Near Infrared Mapping Spectrometer aboard the Galileo spacecraft as it approached the planet's night side on February 10, 1990.
"Bright slivers of sunlit high clouds are visible above and below the dark, glowing hemisphere. The spacecraft is about 100,000 kilometers (60,000 miles) above the planet. An infrared wavelength of 2.3 microns (about three times the longest wavelength visible to the human eye) was used. The map shows the turbulent, cloudy middle atmosphere some 50-55 kilometers (30- 33 miles) above the surface, 10-16 kilometers or 6-10 miles below the visible cloudtops. The red color represents the radiant heat from the lower atmosphere (about 400 degrees Fahrenheit) shining through the sulfuric acid clouds, which appear as much as 10 times darker than the bright gaps between clouds. This cloud layer is at about -30 degrees Fahrenheit, at a pressure about 1/2 Earth's surface atmospheric pressure. Near the equator, the clouds appear fluffy and blocky; farther north, they are stretched out into East-West filaments by winds estimated at more than 150 mph, while the poles are capped by thick clouds at this altitude."
"During the Soviet Venera program, the Venera 11 and Venera 12 probes detected a constant stream of lightning, and Venera 12 recorded a powerful clap of thunder soon after it landed. The European Space Agency's Venus Express recorded abundant lightning in the high atmosphere.
Venus's small induced magnetosphere provides negligible protection to the atmosphere against cosmic radiation. This radiation may result in cloud-to-cloud lightning discharges.
The weak magnetosphere around Venus means the solar wind is interacting directly with the outer atmosphere of the planet. Here, ions of hydrogen and oxygen are being created by the dissociation of neutral molecules from ultraviolet radiation. The solar wind then supplies energy that gives some of these ions sufficient velocity to escape the planet's gravity field. This erosion process results in a steady loss of low-mass hydrogen, helium, and oxygen ions, while higher-mass molecules, such as carbon dioxide, are more likely to be retained.
“Planets which generate magnetic fields in their interiors ... are surrounded by invisible magnetospheres. ... [I]n many respects, the magnetosphere of Venus is a scaled-down version of Earth’s. ... Earth’s magnetosphere is 10 times larger [than that of Venus]”
"During a rare period of very low density solar outflow, the ionosphere of Venus was observed to become elongated downstream, rather like a long-tailed comet. ... Under normal conditions, the solar wind has a density of 5 - 10 particles per cubic cm at Earth's orbit, but occasionally the solar wind almost disappears, as happened in May 1999. ... A rare opportunity to examine what happens when a tenuous solar wind arrives at Venus came 3 - 4 August 2010, following a series of large coronal mass ejections on the Sun. NASA's STEREO-B spacecraft, orbiting downstream from Venus, observed that the solar wind density at Earth's orbit dropped to the remarkably low figure of 0.1 particles per cubic cm and persisted at this value for an entire day."
"The observations show that the night side ionosphere moved outward to at least 15 000 km from Venus' centre over a period of only a few hours," said Markus Fraenz, also from the Max Planck Institute for Solar System Research, who was the team leader and a co-author of the paper. "It may possibly have extended for millions of kilometres, like an enormous tail."
"Although we cannot determine the full length of the night-side ionosphere, since the orbit of Venus Express provides limited coverage, our results suggest that Venus' ionosphere resembled the teardrop-shaped ionosphere found around comets, rather than the more symmetrical, spherical shape which usually exists."
"The side of Venus' ionosphere that faces away from the sun can billow outward like the tail of a comet, while the side facing the star remains tightly compacted, researchers said. ... "As this significantly reduced solar wind hit Venus, Venus Express saw the planet’s ionosphere balloon outwards on the planet’s ‘downwind’ nightside, much like the shape of the ion tail seen streaming from a comet under similar conditions," ESA officials said in a statement today (Jan. 29). It only takes 30 to 60 minutes for the planet's comet-like tail to form after the solar wind dies down. Researchers observed the ionosphere stretch to at least 7,521 miles (12,104 kilometers) from the planet, said Yong Wei, a scientist at the Max Planck Institute in Katlenburg, Germany who worked on this research."
Because of the lack of a planetary magnetic field, the free hydrogen has been swept into interplanetary space by the solar wind.
The clouds of Venus are capable of producing lightning much like the clouds on Earth. The existence of lightning had been controversial since the first suspected bursts were detected by the Soviet Venera probes. In 2006–07 Venus Express clearly detected whistler mode waves, the signatures of lightning. Their intermittent appearance indicates a pattern associated with weather activity. The lightning rate is at least half of that on Earth. In 2007 the Venus Express probe discovered that a huge double atmospheric vortex exists at the south pole of the planet.
Another discovery made by the Venus Express probe in 2011 is that an ozone layer exists high in the atmosphere of Venus.
Venus has an extremely dense atmosphere, which consists mainly of carbon dioxide and a small amount of nitrogen. The atmospheric mass is 93 times that of Earth's atmosphere, while the pressure at the planet's surface is about 92 times that at Earth's surface—a pressure equivalent to that at a depth of nearly 1 kilometer under Earth's oceans. The density at the surface is 65 kg/m³ (6.5% that of water).
On the left are pie charts that show the approximate composition of Venus' atmosphere including some minor constituents.
"HITRAN is a compilation of spectroscopic parameters that a variety of computer codes use to predict and simulate the transmission and emission of light in the atmosphere."
The absence of evidence of lava flow accompanying any of the visible caldera remains an enigma. The planet has few impact craters.
Almost a thousand impact craters on Venus are evenly distributed across its surface. On Venus, about 85% of the craters are in pristine condition. Venusian craters range from 3 km to 280 km in diameter. No craters are smaller than 3 km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy are slowed down so much by the atmosphere, they do not create an impact crater. Incoming projectiles less than 50 meters in diameter will fragment and burn up in the atmosphere before reaching the ground.
The second image down on the right is the crater Mariko.
Addams crater is in the third image down on the right.
"Magellan radar image [is] of Addams crater, Venus. The radar bright outflow associated with the 90 km crater stretches over 600 km to the east. (North is up.) The crater is located at 56.1S,98.9E in the Aino Planitia region."
"The Pioneer Venus Orbiter was the first of a two-spacecraft orbiter-probe combination designed to conduct a comprehensive investigation of the atmosphere of Venus. The spacecraft was a solar-powered cylinder about 250 cm in diameter with its spin axis spin-stabilized perpendicular to the ecliptic plane. A high-gain antenna was mechanically despun to remain focused on the earth. The instruments were mounted on a shelf within the spacecraft except for a magnetometer mounted at the end of a boom to ensure against magnetic interference from the spacecraft. Pioneer Venus Orbiter measured the detailed structure of the upper atmosphere and ionosphere of Venus, investigated the interaction of the solar wind with the ionosphere and the magnetic field in the vicinity of Venus, determined the characteristics of the atmosphere and surface of Venus on a planetary scale, determined the planet's gravitational field harmonics from perturbations of the spacecraft orbit, and detected gamma-ray bursts. UV observations of comets have also been made. From Venus orbit insertion on December 4, 1978 to July 1980 periapsis was held between 142 and 253 km to facilitate radar and ionospheric measurements. Thereafter, the periapsis was allowed to rise (to 2290 km at maximum) and then fall, to conserve fuel. In May 1992 Pioneer Venus began the final phase of its mission, in which the periapsis was held between 150 and 250 km until the fuel ran out and atmospheric entry destroyed the spacecraft the following August."
- Venus has been added between the Earth and the Sun in recorded history.
- The atmosphere of Venus is that of a volcanic planet.
- Magnetic field reversals of the Sun occur with the sunspot cycle which may have its origins in enhanced electron currents from Jupiter and Venus when perihelion is coincident.
- Venus is often confused with Aphrodite (the Moon).
- Venus has "a core of metallized silicates".
- Venus has "an iron core".
- "A chondritic composition of the whole planet" with hypothesis 1.
- "a chondritic mantle" composition with hypothesis 2.
- "a uniform distribution of radioactivity" is a stage of the thermal history of Venus.
- "radioactive elements from the upper 1 000 km were gradually carried out into the crust." is a stage of the thermal history of Venus.
- "This transport [of radioactive elements begins] at the start of the melting of the mantle".
- "The mantle of Venus, as that of the Earth [is] a mixture of different minerals and [melts] in some interval of temperatures [...] of the order of 200°."
- "In the core the melting [occurs] at constant temperature for each given depth."
- "The core [has] a metallic conductivity independent of the temperature."
"Preliminary estimates by Safronov (1965, 1969) of the initial temperature of the Earth were used to choose initial temperatures of Venus and Mercury."
The "molecular conductivity of amorphous matter does not decrease with temperature (as it does in crystalline bodies)."
The "molecular conductivity ceases to depend on temperature with the onset of melting."
For hypothesis 1, the "core of metallized silicates is liquid at the present moment."
For hypothesis 2, "the core is liquid with temperature 12 400 °K."
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