1. Mercury Astronomy 311 Professor Lee Carkner Lecture 10

2. Mercury -- Messenger of the Gods  Closest planet to the Sun, shortest orbital period   Mercury is hard to see since it always appears near the Sun

3. Mercury From Earth

4. Solar Transit of Mercury

5. Viewing Mercury From Earth   Mercury is always near the Sun  Daytime often best for telescope views   Mercury shows phases like Venus   When viewing Mercury, always be careful of the Sun

6. Mercury Facts  Size: 1/3 size of Earth   Orbit: ~0.4 AU   Description: small, airless, cratered

7. Mariner 10   Launched by NASA in 1973   Did not image all of Mercury (only about 45%)

8. Mariner 10

9. Surface of Mercury   Heavily cratered   Scarps or cliffs indicate that Mercury shrank as it cooled  Radar studies indicate that the poles are more reflective than the rest of the planet  Possibly due to water ice in crater shadows

10. Impacts   Impacts have been very common during the history of the solar system   Earth’s weather tends to erase craters  Most occurred during Heavy Bombardment Period, about 3.8 billion years ago

11. Kinetic Energy   Kinetic energy (KE) is released  KE = 1/2 mv 2   v is the velocity (in m/s)   a Watt is a joule per second

12. Caloris Basin   Caused by very large impactor   Not many craters on top of it, so it must be fairly young

13. Geological Map of Caloris Region

14. Spin-Orbit Coupling   The Sun pulls on this bulge slowing down the rotation of the planet (the spin)   Mercury has 3 to 2 spin orbit coupling  due to eccentric orbit, rotation and revolution periods are not quite equal   or 1.5 rotations per orbit

15. Mercury’s Spin-Orbit Coupling

16. Consequences of Spin Orbit Coupling   Mercury has long days and long nights   Day side gets hot, night side gets cold  Day ~700 K, night ~100 K

17. Day and Night on Mercury Sun 700 K (800 F) 100 K (-270 F) Noon Midnight (3 months later) Brrr Ouch!

18. Exosphere  Mercury has a very thin layer of gas called an e  Mercury is too small and too hot to hold a normal atmosphere   Sources:   Solar wind blasting molecules off surface   Water from surface ice?

19. Ions from Mercury’s Exosphere

20. Interior of Mercury  Mercury has a very high density   Why is density so high?   Possibly caused by a large impact stripping off much of the lighter outer layers leaving a disproportionately large core   Why is core molten?  Mercury is small, so core should have cooled

21. Inside Mercury

22. MESSENGER

23. MESSENGER Testing

25. Future Mercury Exploration  The MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) mission   Entered Mercury orbit March 2011   Goals  Detailed surface maps   Study magnetic field 

26. Next Time  Read Chapter 9

27. Summary  Mariner 10 and MESSENGER data reveals Mercury as a small, airless, heavily cratered world  Mercury exhibits 3 to 2 spin orbit coupling due to the Sun’s tidal force  1 1/2 rotations on axis per revolution around the Sun  Mercury has a high density, possibly due to large iron core