Download 11b. Cloud-Covered Venus Venus Data (Table 12

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
0.949 . Earth
•  Mass:
4.9 . 1024 kg
0.815 . Earth
•  Density:
5.24 . water
0.953 . Earth
•  Orbit:
1.1 . 108 km
0.72
•  Day:
•  Year:
AU
– 243.01 days
– 243.01
.
Earth
224.70 days
0.62
.
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
http://upload.wikimedia.org/wikipedia/commons/d/dd/4_Terrestrial_Planets_Size_Comp_True_Color.png
http://www.spacestationinfo.com/images/venus-phase1.gif
Venus As Seen From Earth
Orbits of Venus & 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°
•  Greatest western elongation is ~ 47°
Evening
Morning
Venus’s Greatest Elongations
Venus’s Atmosphere: A First Look
Eastern (Evening)
Western (Morning)
•  Venus is perpetually cloud-covered
1 November 2013
22 March 2014
–  This makes Venus extremely bright
6 June 2015
26 October 2015
12 January 2017
3 June 2017
17 August 2018
6 January 2019
24 March 2020
13 August 2020
–  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
Prograde & Retrograde Rotation
Venus’s a Hot, Dense Atmosphere
•  Insolation
[Incoming solar radiation]
–  Venus averages ~ 0.72 AU from the Sun
•  1 / 0.722 = 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
–  CO2 is extremely common in volcanic eruptions
•  CO2 is an excellent absorber of infrared [heat] radiation
•  An important comparison
–  Venus: 96.5% CO2 increases temperature ~ 400°C
–  Earth: 0.04% CO2 increases temperature ~ 36°C
Volcanic Eruptions Produce Clouds
Venusian Cloud Layers
•  Atmospheric sulfur compounds
–  Fractional amounts
•  Venus
•  Earth
~1.5 . 10–2 of all atmospheric gases
~1.0 . 10–9 of all atmospheric gases
–  Venus has ~ 93 times more atmosphere than Earth
•  Venus’s air has ~ 1.35 109 x more sulfur than Earth’s air
•  Probable cause
–  Like CO2, sulfur is common in volcanic eruptions
•  No oceans to absorb this sulfur
•  Instances of increased Venusian sulfur levels
–  Late 1950’s
–  Late 1970’s
Earth-based observations
Pioneer Venus Orbiter
Venera 13 Images Venus’s Surface
Venusian rocks appear orange because of cloud colors.
The same picture corrected to remove atmospheric colors.
1 March 1982
Venusian Atmospheric Circulation
Venusian Climatic Evolution
•  Expected signs
•  Proto-atmospheres
–  Venus & Earth were probably remarkably similar
•  Countless volcanic eruptions provided H2O, CO2 & SO2
–  Globe-circling volcanic mountain chains
–  Extensive sets of transform faults
–  Extremely long subduction trenches
•  Observed signs
•  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
Volcanoes On Venus & Earth
Venus
0% oceans
Gas enters atmosphere
High CO2 & SO2 concentrations
Yellow sky
Venus Shows No Plate Tectonics
–  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
Venus: A Mercator Projection
Earth
~ 70% oceans
Gas absorbed by oceans
Low CO2 & SO2 concentrations
Blue sky
Venus: A Global Perspective
Volcanic Activity On Venus & Earth
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
Important Concepts
• 
• 
• 
–  Retrograde, once in ~243 Earth days
–  Uranus & Pluto also retrograde
•  Venera 12 operated ≥110 minutes on 21 December 1978
–  Voyager missions
•  Primarily orbiters with low-resolution radar images
–  Magellan mission
•  High-resolution radar images of almost the entire surface
Axial rotation
• 
The Venusian atmosphere
–  Basic properties
•  Dominance of CO2 & SO2
•  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
Perpetual cloud cover
–  Obscures the Venusian surface
–  Encircles the planet in only ~4 days
–  Radar needed to penetrate clouds
•  Venera 4 entered the atmosphere on 18 October 1967
•  United States
• 
–  Very bright & excellent elongations
–  Distinct phases much like the Moon
•  10 of 16 spacecraft successfully arrived at Venus
•  Venera 7 soft-landed on 15 December 1970
Venus as seen from Earth
•  Abundant pancake domes
• 
Spacecraft exploration of Venus
–  Russia
–  United States