Venus Data (Table 12-1) 11b. Cloud-Covered Venus. Venus Data: Numbers. Venus Data: Special Features. Venus Phases & Angular Diameters

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1 11b. Cloud-Covered Venus Venus Data (Table 12-1) The Venusian atmosphere Venus has slow retrograde rotation Venus has a hot dense atmosphere Volcanic eruptions form Venusian clouds Climatic evolution on Venus Venus shows no evidence of plate tectonics Venus Data: Numbers Venus Data: Special Features Diameter: 12,104.km Earth Mass: kg Earth Density: water Earth Orbit: km 0.72 Day: Year: AU days Earth days Earth Venus is the second planet from the Sun Venus is the second largest terrestrial planet Venus has many active volcanoes Venus is almost a twin of the Earth except Venus has ~ 93 times Earth s atmosphere Venus atmosphere is ~ 96% CO2 Venus is perpetually cloud covered Venus average surface temperature is ~ 480 C Venus surface can be seen only with radar Venus is very easy to observe from Earth Venus is seen as much as 47 away from the Sun Venus goes through phases much like the Moon Venus Phases & Angular Diameters Relative Sizes of Terrestrial Planets

2 Venus As Seen From Earth Venus is outshone only by the Sun & Moon Venus is very close to the Sun Venus is ~ 0.7 AU from the Sun Venus is very close to the Earth Venus is ~ 0.3 AU from the Earth at inferior conjunction Venus is very large Venus is ~ 95% the diameter of Earth Venus has an albedo of ~ 0.59 Venus is perpetually cloud-covered Venus has large elongations The Venusian orbit is nearly circular Greatest eastern elongation is ~ 47 Evening Greatest western elongation is ~ 47 Morning Orbits of Venus & Earth Venus s Greatest Elongations Eastern (Evening) Western (Morning) 1 November March June October January June August January March August 2020 Venus s Atmosphere: A First Look Venus is perpetually cloud-covered This makes Venus extremely bright Cloud details are best seen with ultraviolet λ s Surface details are only seen with radar λ s Earth-based imaging systems Magellan orbital mission The Venusian atmosphere is extremely dense About 93 times more than Earth Venus Seen In Ultraviolet Light Venus s Slow Retrograde Rotation Observational difficulties Perpetual cloud cover obscures the surface Surface can be seen only using radar λ s Clouds encircle the planet in ~ 4 days Best seen in UV λ s Successful observations Doppler shift analyses in the early 1960 s Transmit one precise λ Receive a slightly spread out range of λ s One edge of Venus is moving toward Earth One edge of Venus is moving away from Earth Results Venus rotates on its axis in a retrograde direction Uranus & Pluto also exhibit retrograde axial rotation Venus s day is ~ 243 Earth days long

3 Prograde & Retrograde Rotation Venus s a Hot, Dense Atmosphere Insolation [Incoming solar radiation] Venus averages ~ 0.72 AU from the Sun 1 / = 1 / 0.52 = ~ 1.93 > sunlight than Earth Venus would be hotter even w/earth s atmosphere Venusian environment Intense sunlight evaporated Venus s oceans Volcanic gases directly enter Venus s atmosphere Most of Earth s volcanic gases dissolve in ocean water CO 2 is extremely common in volcanic eruptions CO 2 is an excellent absorber of infrared [heat] radiation An important comparison Venus: 96.5% CO 2 increases temperature ~ 400 C Earth: 0.04% CO 2 increases temperature ~ 36 C Volcanic Eruptions Produce Clouds Atmospheric sulfur compounds Fractional amounts Venus ~ of all atmospheric gases Earth ~ of all atmospheric gases Venus has ~ 93 times more atmosphere than Earth Venus s air has ~ x more sulfur than Earth s air Probable cause Like CO 2, sulfur is common in volcanic eruptions No oceans to absorb this sulfur Instances of increased Venusian sulfur levels Late 1950 s Earth-based observations Late 1970 s Pioneer Venus Orbiter Venusian Cloud Layers Venera 13 Images Venus s Surface Venusian Atmospheric Circulation Venusian rocks appear orange because of cloud colors. The same picture corrected to remove atmospheric colors. 1 March 1982

4 Venusian Climatic Evolution Proto-atmospheres Venus & Earth were probably remarkably similar Countless volcanic eruptions provided H 2 O, CO 2 & SO 2 Proto-Sun Infant Sun produced only ~70% of today s energy All stars gradually increase their energy output Climatic evolution Infant Venus was cool enough to have liquid water Single-celled life forms may have evolved on Venus Juvenile Venus became too hot to have oceans The same fate faces Earth in ~ 1 billion years Venus Shows No Plate Tectonics Expected signs Globe-circling volcanic mountain chains Extensive sets of transform faults Extremely long subduction trenches Observed signs No elongated volcanic mountain chains Substantial evidence of hot-spot volcanoes No confirmed transform faults No confirmed subduction trenches Probable cause No oceans to affect subduction zone activity Venusian lithosphere is too hot & soft to sustain forces Subducted water promotes lower temperature melting Flake [Blob] tectonics Pancake domes Volcanoes On Venus & Earth Venus: A Mercator Projection Venus Earth 0% oceans ~ 70% oceans Gas enters atmosphere Gas absorbed by oceans High CO 2 & SO 2 concentrations Low CO 2 & SO 2 concentrations Yellow sky Blue sky Venus: A Global Perspective Volcanic Activity On Venus & Earth

5 Aine Corona With Pancake Domes Solar System s Longest Channel Theia Mons (Earth Radar Image) Maat Mons (Vertical Exag. = 22.5) Spacecraft Exploration of Venus Russia Venera missions 10 of 16 spacecraft successfully arrived at Venus Venera 4 entered the atmosphere on 18 October 1967 Venera 7 soft-landed on 15 December 1970 Venera 12 operated 110 minutes on 21 December 1978 United States Voyager missions Primarily orbiters with low-resolution radar images Magellan mission High-resolution radar images of almost the entire surface Important Concepts Venus as seen from Earth Very bright & excellent elongations Distinct phases much like the Moon Perpetual cloud cover Obscures the Venusian surface Encircles the planet in only ~4 days Radar needed to penetrate clouds Axial rotation Retrograde, once in ~243 Earth days Uranus & Pluto also retrograde The Venusian atmosphere Basic properties Dominance of CO 2 & SO 2 High temperature & pressure Apparent lack of liquid water Evolution Initially much like Earth s atmosphere Solar radiation increased ~30% No plate tectonics on Venus None of the classic evidence Absence of oceans probably the cause Evidence of blob tectonics Abundant pancake domes Spacecraft exploration of Venus Russia United States