The Terrestrial Planets, Part I

1. The Terrestrial Planets, Part I Mercury and Venus

2. MERCURYThe Winged Messenger

3. Physical Data • Diameter: 4,864 km (0.382 Dearth) • Mass: 3.33x1026 g (0.0558 Mearth) • Density: 5.50 g/cm3 • Rotation Period: 58.65 days • Tilt of Axis: 0o • Surface Temperature: 700 K (day side) . 100 K (dark side)

4. Physical Data • Orbital Semi-Major Axis: 0.387 AU Perihelion Distance: 0.308 AU Aphelion Distance: 0.467 AU • Orbital Period : 87.97 days (0.241 years) • Orbital Inclination: 7.00o • Orbital Eccentricity: 0.206 • Surface Gravity: 0.38 Earth gravity

5. Physical Data • Maximum Elongation: 28o (aphelion) 18o (perihelion) . 23o (average) • Satellites: None • Magnetic Field: 1% strength of Earth’s

6. Mercury Apparitions • At western elongation, Mercury is visible in the morning before dawn (“morning star”). • At eastern elongation, Mercury is visible in the evening after sunset (“evening star”). • Mercury appears to change in size, and has phases like the Moon.

7. Once thought to be synchronous Mercury rotates 3 times for every two orbits One Mercury “day” lasts two Mercurian years! Mercury’s 3:2 Resonance

8. Mercury is the most iron-rich planet in the solar system. Of all the planets, Mercury has the largest core relative to its overall volume (42%, 16% for Earth) Mercury’s Interior

9. Mercury’s Magnetic Field • 1% Earth’s Magnetic Field SUN

10. Mercury appears very Moon-like Mercury’s Surface

11. Mercury’s Surface • Craters

12. Mercury’s Surface • Lobate Scarps

13. Mercury’s Surface • Caloris Basin - 1300 km diameter crater

14. Mercury’s Surface • “Weird” (or Jumbled) Terrain • Polar caps?

15. Other Topics: • Precession of perihelion • Radar measurements of Mercury’s rotation

16. VENUSThe Goddess of Love

17. Physical Data • Diameter: 12,104 km (0.951 Dearth) • Mass: 4.87x1027 g (0.815 Mearth) • Density: 5.30 g/cm3 • Rotation Period: 243 days • Tilt of Axis: 177.4o (retrograde) • Suface Temperature: 750 K

18. Physical Data • Orbital semi-major axis: 0.723 AU • Orbital period: 224.70 days (0.615 years) • Orbital inclination: 3.39o • Orbital Eccentricity: 0.007 • Maximun Elongation: 48o • Surface Gravity: 0.90 Earth gravity

19. Physical Data • Satellites: None • Magnetic Field: No • Surface Pressure: 90 times Earth’s!

20. Venus Apparitions • At western elongation, Venus is visible in the morning before dawn (“morning star”). • At eastern elongation, Venus is visible in the evening after sunset (“evening star”). • Venus appears to change in size, and has phases like the Moon

21. Clouds whiz aroud Venus at 300 km/hr. At this speed, a cloud can circle Venus in only four days. Clouds are composed of mostly sulfuric acid and water. Clouds of Venus

22. The Atmosphere of Venus • 96.5% Carbon Dioxide • 3% Nitrogen • Traces of Other Gases: 0.019% Sulfur Dioxide 0.01% Water Vapor 0.007% Argon Hydrochloric acid, Hydroflouric acid • Atmospheric Pressure 90x Earth’s

23. Clouds contain sulfuric acid and water Cloud tops appear yellow from sulfur dust Temperature reaches a maximum at the surface of about 750 K (900o F) 105 km Venus’ Atmosphere 75 km Top of Clouds Upper Cloud Deck 60 km Droplets of Sulfuric Acid & Water Altitude Haze Layer Lower Cloud Deck 45 km Sulfuric Acid& Water and Sulfur Crystals Clouds T hin Out 30 km Clear, Hot Atmosphere 15 km 0 km 0 K 200 K 400 K 600 K 800 K Temperature

24. Why is Venus So Hot?

25. Core - 12% total volume of planet Molten core? Thin crust, with continent sized features. Venus’ Interior Venus CRUST ( silicates) 6052 km 3616 km CORE ( iron-nickel ) MANTLE ( olivine )

26. Soviet Venera Missions • First Surface Photographs, 1970 Photo from Venera 13

27. The Magellan Mission

28. Suface Features: Impact Craters Lava Flows Volcanic Calderas Volcanoes Peculiar to Venus: Coronae, Pancake . Domes, Ticks, Graph Paper Regions Magellan Surface Imagery

29. Venus’ Surface • Graph Paper Regions

30. Venus’ Surface • “The Tick”

31. Venus’ Surface • Coronae

32. Venus’ Surface • Pancake Domes