1. 11b. Cloud-Covered Venus 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

2. Venus Data (Table 12-1)

3. Venus Data: Numbers Diameter: 12,104.km 0.949 . Earth
Mass: kg Earth
Density: water Earth
Orbit: km AU
Day: – days – Earth
Year: days Earth

4. Venus Data: Special Features
Venus is the second terrestrial planet from the Sun
Venus is the second largest terrestrial planet
Venus almost certainly has active volcanoes
Venus is almost a twin of the Earth except that…
Venus has ~100 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

5. Greatest Elongations of Venus
2010 None August 20

6. 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 sky
Greatest western elongation is ~ 47° Morning sky

7. Orbits of Venus & Earth

8. The Venusian Atmosphere: A First Look
Venus is perpetually cloud-covered
This makes Venus extremely bright
Cloud details are best seen with UltraViolet l’s
Surface details are only seen with radar l’s
Earth-based imaging systems
Magellan orbital mission
The Venusian atmosphere is extremely dense
Nearly 100 times more than Earth

9. Venus Seen In Ultraviolet Light

10. Venus Has Slow, Retrograde Rotation
Observational difficulties
Perpetual cloud cover obscures the surface
Surface can be seen only using radar l’s
Clouds encircle the planet in ~4 days
Best seen in UV l’s
Successful observations
Doppler shift analyses in the early 1960’s
Transmit one precise l
Receive a slightly spread out range of l’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

11. Prograde & Retrograde Axial Rotation

12. Venus Has a Hot, Dense Atmosphere
Insolation [Incoming solar radiation]
Venus is ~0.7 AU from the Sun
1 / 0.72  =  1 / 0.49  =  ~2.0 greater sunlight intensity than Earth
Even with Earth’s atmosphere, Venus would be hotter
Venusian environment
More intense sunlight evaporated Venusian oceans
Volcanic gases directly enter the Venusian atmosphere
On Earth, most volcanic gases are dissolved in ocean water
CO2 is extremely common in volcanic eruptions
CO2 is an excellent absorber of infrared [heat] radiation
An important comparison
On Venus,  96.5% CO2 increases temperature ~400°C
On Earth, 0.035%CO2 increases temperature ~  36°C

13. Volcanic Eruptions Produce Clouds
Atmospheric sulfur compounds
Fractional amounts
Venus ~1.5 . 10–2 of all atmospheric gases
Earth ~1.0 . 10–9 of all atmospheric gases
But Venus has ~90 times more atmosphere than Earth
Venus has ~1.35 billion x more atmospheric sulfur than Earth
Probable cause
Like CO2, sulfur is common in volcanic eruptions
No oceans to absorb this either
Instances of increased Venusian sulfur levels
Late 1950’s Earth-based observations
Late 1970’s Pioneer Venus Orbiter

14. Venusian Cloud Layers

15. Venera 13 Images at Venus’s Surface
Venusian rocks appear orange because of cloud colors.
The same picture corrected to remove the atmospheric colors.

16. Venusian Atmospheric Circulation

17. Venusian Climatic Evolution
Proto-atmospheres
Both Venus & Earth were probably remarkably similar
H2O, CO2 & SO2 provided by extensive volcanic eruptions
Proto-Sun
Initially, the Sun produced only ~70% the energy as now
All stars gradually increase their energy output
Climatic evolution
Initially, Venus was cool enough to have liquid water
Life may even have evolved on Venus
Eventually, Venus got hot enough to evaporate oceans
The same fate almost certainly faces Earth in ~1 billion years

18. 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 cool & lubricate subduction zone activity
Venusian lithosphere too hot & too soft to sustain forces
Subducted water promotes melting at lower temperatures
“Blob tectonics” Pancake domes

19. Volcanoes On Venus & Earth
0% oceans ~ 70% oceans
Vented gas enters atmosphere Vented gas absorbed by oceans
High CO2 & SO2 concentrations Low CO2 & SO2 concentrations
Yellow sky Blue sky

20. Venus: A Mercator Projection

21. Venus: A Global Perspective

22. Volcanic Processes On Venus & Earth

23. Aine Corona With Pancake Domes

24. The Solar System’s Longest Channel

25. Theia Mons (Earth-Based Radar Image)

26. Maat Mons (Vertical Exaggeration = 22.5)

27. Spacecraft Exploration of Venus
Russia
Venera missions
Several of these landed on Venus
United States
Voyager missions
Primarily orbiters with low-resolution radar images
Magellan mission
High-resolution radar images of almost the entire surface

28. Important Concepts Venus as seen from Earth Perpetual cloud cover
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 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
Abundant pancake domes
Spacecraft exploration of Venus
Russia
United States