1. Venus Astronomy 311 Professor Lee Carkner Lecture 11

2. Why does Mercury have 3-2 spin orbit coupling instead of 1-1? a)Because of the Caloris impact b)Due to resonance with Venus c)Because of its large iron core d)Because it is not quite close enough to the sun e)Because of the relatively high eccentricity of its orbit

3. Why do we think there might be water ice at Mercury’s poles? a)Radar reflects strongly off of polar regions b)We see the spectroscopic signature of hydrogen c)The Caloris impactor should have lowered temperatures at the poles enough for ice to form d)There is evidence of comet impacts at the poles e)The slow rotation of Mercury is ideal for ice formation

4. Venus -- The Goddess of Beauty   Romans named it Venus for its beauty  symbol for Venus is a mirror

5. Venus from Earth   sometimes called the morning or evening “star”   Venus is covered with clouds  clouds reflect ~75% of sunlight

6. Venus Facts  Size: 95% Earth   Orbit: 0.7 AU   Description: Earth-sized, hot, thick atmosphere (Earth’s evil twin)

7. Venus’s Retrograde Rotation  When viewed from above the north pole of the Earth, most of the planets:   revolve around the Sun counterclockwise   It is upside down  Why is Venus upside down?   We have no evidence of this, however

8. Retrograde Rotation

9. Rotation Rate   Venus revolves around the Sun with a period of 225 days   Reason is unclear   impact altered its rotation rate?

10. Venus from Pioneer

11. Venus’s Atmosphere   Composition:     Pressure: 90 atmospheres (equal to being 1 km underwater on Earth)  Temperature: 750 K (hottest planet in solar system)

12. Chemicals in Atmosphere   Forms many sulfur compounds including sulfuric acid (H 2 SO 4 )  Sulfuric acid has vapor point such that it boils on the surface but condenses in the atmosphere to form clouds   Also, hydrofluoric acid (HF), hydrochloric acid (HCl) and other corrosive compounds

13. Temperature in Atmosphere

14. Formation of Atmosphere 1) 2) Water produces greenhouse effect, boils oceans 3) 4) With no water, CO 2 cannot be removed from atmosphere, thick CO 2 atmosphere forms 5) 6) Volcanoes outgas sulfur, forms sulfuric acid clouds

15. The Surface of Venus  Clouds block blue light so surface appears red, but surface is actually gray   Chemical analysis indicates that surface rocks are similar to basalt, a volcanic rock

16. Interlude Planetary Configurations

17. Magellan Maps Venus   Probes and landers saw only bits and pieces of it   Used radar to penetrate the clouds and map the surface with a resolution of 100 meters

18. Radar Map of Venus

19. Global Surface of Venus   Two large highlands or continents (Aphrodite Terra and Ishtar Terra)   The entire surface is the same age  Venus re-surfaces itself   Surface features named after women

20. Volcanism on Venus  Evidence for Volcanism:   sulfur in atmosphere   filled craters   Note that volcanoes are not active now

21. The Interior of Venus  With so much volcanism, part of Venus must be molten, but:   the crust is not broken up into moving plates   Why no plate tectonics?  too hot or too dry?   Venus probably has a molten core 

22. Next Time  Read Chapter 7

23. Summary  Earth-Sized, hot, thick atmosphere  (Earth’s evil twin)  Rotates slowly and upside-down  Studied by Venera landers and Magellan radar mapper

24. Summary: Atmosphere  Composed of CO 2 with sulfuric acid clouds  Thick (90 atmospheres) :  No water to wash out CO 2  Hot (750 K):  Powerful greenhouse effect

25. Summary: Surface  Volcanism shapes surface and outgases sulfur  See volcanoes and lava flow channels  Surface mostly flat with a few highlands  Nature of core is unknown