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Cloud-Covered Venus

5.243 g/cm3The surface of Venus is hidden beneath a thick,highly reflective cloud coverVenus is similar to the Earth in its size, mass, average density, and surface gravityIt is covered by unbroken, highly reflective clouds that conceal its other features from Earth-based observers

Venuss murky past (and atmosphere)Because it was similar is size and solar system position, many people have called it the twin of Earth.Because we couldnt see through the clouds, a great number of interesting hypotheses came into existence about its surface.None of those hypotheses were correct.Early Discovery From AfarMotion in our skyOrbit and rotationAtmosphere (atmosphere and cloud composition, cloud motion)

Venus can be seen in the eastern sky in the hours before dawn for several months around the greatest western elongation.

It can be seen in the western sky in the hours after dusk for several months around greatest eastern elongation.

At its greatest eastern and western elongations, Venus is about 47 from the Sun.Greatest Elongations of VenusEast (evening)West (morning)2013Nov12014Mar222015Jun62015Oct262017Jan122017Jun32018Aug172019Jan62020Mar242020Aug132021Oct292022Mar202023Jun42023Oct232025Jan102025Jun12026Aug152027Jan32028Mar222028Aug10Greatest Elongations of Venus

The upper cloud layers of the Venusian atmosphere move rapidly (300 km/hr) around the planet in a retrograde direction (with rotation), with a period of only about 4 Earth days.

The circulation of the Venusian atmosphere is dominated by two huge convection currents in the cloud layers, one in the northern hemisphere and one in the southern hemisphereSouth Pole Double Vortex!

Then we went exploring!Venus Express - ESA Venus Orbiter (2006) (Currently in Orbit) MESSENGER - NASA Mercury Orbiter (2004) (Two Venus Flybys in 2006 and 2007)Magellan - NASA Venus Radar Mapping Mission (1989-1994) Pioneer Venus - NASA Orbiter/Probes to Venus (1978-1992) Galileo - NASA Mission to Jupiter (Venus flyby - 1990) Vega 1 - Soviet mission to Venus and Comet Halley (Venus flyby - 1985) Vega 2 - Soviet mission to Venus and Comet Halley (Venus flyby - 1985) Venera - Soviet Venus Missions (1-16) (1961-1983) Mariner 10 - NASA Mission to Venus and Mercury (1973-1975) Mariner 5 - NASA Venus flyby (1967) Mariner 2 - NASA Venus flyby (1962)

In 1962 the unmanned U.S. spacecraft Mariner 2 made the first close flyby of Venus Scientific discoveries made by Mariner 2 included a slow retrograde rotation rate for Venus, hot surface temperatures and high surface pressures, a predominantly carbon dioxide atmosphere, continuous cloud cover with a top altitude of about 60 km, and no detectable magnetic field. Venuss rotation is slow and retrograde

Venus rotates clockwise, with period slightly longer than orbital period.Possible reasons: Off-center collision with massive protoplanet Tidal forces of the sun on molten coreVenus rotates slowly in a retrograde direction with a solar day of 117 Earth days and a rotation period of 243 Earth days

There are approximately two Venusian solar days in a Venusian year.

Spectra Comparison

Spectra taken of Venus showed mostly Carbon Dioxide in the atmosphere.

The clouds were shown to be sulfuric acid!

This is a comparison showing Carbon Dioxide in the Venusian, Terran, and Martian atmospheres Venera 16 - Soviet Venus Orbiter (1983) Venera 15 - Soviet Venus Orbiter (1983) Venera 14 - Soviet Venus Lander (1981) (Images and soil samples similar to oceanic basalts) Venera 13 - Soviet Venus Lander (1981) (Images and soil samples) Venera 12 - Soviet Venus Lander (1978) Venera 11 - Soviet Venus Lander (1978) Venera 10 - Soviet Venus Orbiter and Lander (1975)Preliminary results provided: (A) profile of altitude (km)/pressure (earth atmospheres)/temperature (deg C) of 42/3.3/158, 15/37/363, and 0/92/465, (B) successful TV photography showing large pancake rocks with lava or other weathered rocks in between, and (C) surface wind speed of 3.5 m/s. Venera 9 - Soviet Venus Orbiter and Lander (1975)Preliminary results indicated: (A) clouds 30-40 km thick with bases at 30-35 km altitude, (B) atmospheric constituents including HCl, HF, Br, and I, (C) surface pressure about 90 (earth) atmospheres, (D) surface temperature 485 deg C, (E) light levels comparable to those at earth midlatitudes on a cloudy summer day, and (F) successful TV photography showing shadows, no apparent dust in the air, and a variety of 30-40 cm rocks which were not eroded. Venera 8 - Soviet Venus Lander 1972Venus atmospheric probe and lander. Confirmed high surface temperature. Ran 50 min. Cloud layer floor. Rock similar to granite? Venera 7 - Soviet Venus Lander 1970 first man-made object to return data after landing on another planet, hit at 38 mph at 50 angle, bumpy ride and parchute rip, got temp, was barely functional 23 min after landing Venera 6 - Soviet Venus Probe 1969, chemical readings Venera 5 - Soviet Venus Probe 1969, chemical readings Venera 4 - Soviet Venus Probe 1967, 95% CO2, crashed after battery died. Venera 3 - Soviet Venus Lander (Contact Lost) - 1965 Venera 2 - Soviet Venus Flyby (System Failed) - 1965 Venera 1 - Soviet Venus Flyby (Contact Lost) 1961, data on magnetic fields, cosmic rays and solar plasma.VeneraAtmospheric StudiesResults reported included evidence of lightning and thunder, a high Ar36/Ar40 ratio, and the discovery of carbon monoxide at low altitudes.Radar MappingThe Atmosphere of Venus

Spacecraft measurements reveal that 96.5% of the Venusian atmosphere is carbon dioxide

Most of the rest of the atmosphere is nitrogen.

The bottom 30 km is clear of clouds or haze.There is 150 x more Deuterium per H atom than on Earth.New data shows atmosphere up to 90 km on night side!Venus has a hot, dense atmosphere and corrosivecloud layersVenuss clouds consist of droplets of concentrated sulfuric acid. The haze is also sulfuric acid.The surface pressure on Venus is 90 atm, and the surface temperature is 460C (close to 900F)!Both temperature and pressure decrease as altitude increases

Cold Layer found!A new analysis based on five years of observations using ESAs Venus Express, scientists have uncovered a very chilly layer at temperatures of around 175C in the atmosphere 125 km above the planets surface. The curious cold layer is far frostier than any part of Earths atmosphere, for example, despite Venus being much closer to the Sun. The discovery was made by watching as light from the Sun filtered through the atmosphere to reveal the concentration of carbon dioxide gas molecules at various altitudes along the terminator the dividing line between the day and night sides of the planet. Armed with information about the concentration of carbon dioxide and combined with data on atmospheric pressure at each height, scientists could then calculate the corresponding temperatures.

1 October 2012 Venus Express has spied a surprisingly cold region high in the planets atmosphere that may be frigid enough for carbon dioxide to freeze out as ice or snow. Ozone Layer found!6 October 2011 ESAs Venus Express spacecraft has discovered an ozone layer high in the atmosphere of Venus.

The ozone was detectable because it absorbed some of the ultraviolet from the starlight.

These atoms are then swept around to the nightside of the planet by winds in the atmosphere: they can then combine to form two-atom oxygen molecules, but also sometimes three-atom ozone molecules.

Its ozone layer sits at an altitude of 100 km, about four times higher in the atmosphere than Earth's and is a hundred to a thousand times less dense.

The Atmosphere of VenusVenus is the victim of a runaway greenhouse effect just kept getting hotter and hotter as infrared radiation was reabsorbed

Venera 13 Mosaic

Venera 13Venera 14Venera 13 Mosaic

Venera 13 - terrainVenera 14 - terrainVenera-13 revealed rolling hills with layered slabs of rock and soil. From high resolution radar imaging of the landing site, Russian geologists concluded that Venera-13 probably landed on the most common type of Venusian terrain, plains with wrinkle ridges. These are the oldest volcanic plains, formed about 750 million years ago, fractured and buckled by tectonic pressures in the crust.

Potassium-rich basalts.Venera-14 saw a flat expanse of rock with no soil. Radar imaging of the site reveals a younger volcanic plain with lobate flows of lava, probably formed a few million years ago. The rock is actually layered and crunchy. One new theory suggests it is a pumice-like material, formed out of volcanic ash or dust from meteorite strikes.

Similar to ocean floor basalts.Credit: Don P. Mitchell

Credit: Don P. MitchellIshtar Terra , topographic, data from Venera and Magellan

The Surface of VenusSurface Features on Venus

Smooth lowlandsHighland regions:Maxwell Montes are ~ 50 % higher than Mt. Everest!RadarBest mapping technique: use radar to penetrate clouds Radar systems emit a short burst of radio waves and then detect the reflected burst to determine a target's distance and (through the Doppler effect) motion. Interpreting radar images: brighter regions are more reflective of radar waves, meaning they are rougher. Darker regions are smoother. Radar Map of Venus (Pioneer, 1981)

And then came MagellanRadar Map of Venuss SurfaceSurface features shown in artificial colors Scattered impact craters Volcanic regions Smooth lava flows

Volcanism on Venus

Sapas Mons (radar image)2 lava-filled calderas

~ 400 km (250 miles)Lava flows

The Surface of VenusVolcanoes on Venus:

Above: Sif MonsRight: Gula MonsCluster of Cone Volcanoes

Volcanic Features on Venus

Baltis Vallis: 6800 km long lava flow channel (longest in the solar system!)Aine Corona

Pancake Domes:Associated with volcanic activity forming coronae

Coronae: Circular bulges formed by volcanic activity

Some lava flows collapsed after molten lava drained away

The density of craters suggests that the entire surface of Venus is no more than a few hundred million years old.

According to the equilibrium resurfacing hypothesis, this happens because old craters are erased by ongoing volcanic eruptions

Venusian Surfaces

Lakshmi Planum and Maxwell Mountains

Radar imageWrinkled mountain formations indicate compression and wrinkling, though there is no evidence of plate tectonics on Venus.How do you get mountains?If it is so hot, how do the mountains stay upright and not flow away as they start to melt?If you bake rock, you make it harder!The Surface of VenusVenuss largest impact crater, named after Margaret Mead:

Incoming!Craterless Splotch

Crater Cluster

Dark HaloCraters on Venus

~900 impact craters on Venuss surface: Surface not very old.No water on the surfaceThick, dense atmosphere (filters out 90% of objects smaller than 9 km in diameter) No erosion Craters appear sharp and fresh (86% pristine)The Crater StoryPristine CratersRandomly scattered (with respect to elevation, terrain type, etc.)Relatively few craters

Resurfacing Event!About 91.5% resurfaced between 500 and 750 million years ago!The Other 8.5%?Tesserae

The climate on Venus followed a differentevolutionary path from that on EarthVenuss high temperature is caused by the greenhouse effect, as the dense carbon dioxide atmosphere traps and retains energy from sunlight.The early atmosphere of Venus contained substantial amounts of water vaporThis caused a runaway greenhouse effect that evaporated Venuss oceans and drove carbon dioxide out of the rocks and into the atmosphereAlmost all of the water vapor was eventually lost by the action of ultraviolet radiation on the upper atmosphere.The Earth has roughly as much carbon dioxide as Venus, but it has been dissolved in the Earths oceans and chemically bound into its rocksVolcanic eruptions are probably responsiblefor Venuss cloudsVenuss clouds consist of droplets of concentrated sulfuric acidActive volcanoes on Venus may be a continual source of this sulfurous material

Venuss Magnetic Field and Internal StructureNo magnetic field, probably because rotation is so slow (or because core is solid?)No measurements available that would give clues to internal structureGravity data by Magellan is controversialSolar wind and atmosphere interactionDuring normal solar windDuring reduced solar wind

A History of Venus

Complicated history; still poorly understood.Very similar to Earth in mass, size, composition, density, but no magnetic field Core solid? Solar wind interacts directly with the atmosphere, forming a bow shock and a long ion tail. CO2 produced during outgassing remained in atmosphere (on Earth: dissolved in water).Heat transport from core mainly through magma flows close to the surface ( coronae, pancake domes, etc.)Any water present on the surface rapidly evaporated feedback through enhancement of greenhouse effect