1. The Terrestrial Planets Astronomy 311 Professor Lee Carkner Lecture 9

2. Early Missions to the Inner Planets  1962 -- Mariner 2 Venus Fly-by   1964 -- Mariner 4 Mars Fly-by   1970 Venera 7 Venus lander   1973 Mariner 10 Venus/Mercury Fly-by   1975 Viking 1 and 2 Mars lander 

3. Planetary Probes  Large number of missions from 1960-1978   Almost all planetary missions from the US or the USSR    Future missions may be more multinational

4. US and Soviet Planetary Missions  Very large number of Soviet missions, most were failures  Venus:  Most notable success was the Venus Venera landers  Mars:  Smaller number of US missions, but higher success rate  Mercury:  Venus:  Mars:

5. Sources of Information for the Inner Planets  Mercury:  Mariner 10 --  Venus:  Soviet Venera landers --  Magellan --  Mars:  Viking, Pathfinder, Spirit, Opportunity --  Viking, Global Surveyor, Odyssey --

6. Inner Planet Facts  Mercury  Diameter: 0.38  Mass: 0.06   Venus  Diameter: 0.95  Mass: 0.82   Earth  Diameter: 1  Mass: 1   Mars  Diameter: 0.53  Mass: 0.11 

7. Determining Planetary Properties  Mass   Distance   Diameter 

8. Determining Planetary Properties (cont.)  Average Density   Atmospheric composition 

9. The Planets That Weren’t  There should have been 2 other inner planets  The Moon Impactor   The Asteroid Belt 

10. The Moon and the Earth

11. The Moon

12.  First visited in 1959 by Luna 1 (USSR)   Moon facts  Diameter: 0.27  Mass: 0.01  Orbital Radius (from Earth): 0.003 

13. Moons of the Inner Planets  Venus and Mercury have no moons  Earth has one large moon   Mars has two moons, Phobos and Deimos   Inner planets may be too small to capture moons easily 

14. Asteroids  Millions of small bodies orbit the Sun, most between Mars and Jupiter (the asteroid belt)   Meteors   Spacecraft 

15. Asteroid Facts  Asteroids  Diameter: <0.14  Mass: <0.02  Orbital Radius: 2.8   Most have orbits within the asteroid belt (~2-3.5 AU)

16. The Asteroid Gaspra

17. Sizes of the Inner Planets  Sizes relative to Earth  Earth:  Venus:  Mars:  Mercury:  Moon:  Asteroid:  All are small compared to the gas giants (Neptune is ~4 times the diameter of the Earth and ~64 times the volume)

18. Composition  All of the inner planets have about the same density (~5000 kg/m 3 )   What makes up the difference?     “Rocky” planets could also be called the “metal” planets

19. Composition (cont.)  Earthquake studies indicate that the Earth has a iron core    We believe that the other inner planets have a similar structure 

20. Interior Structure

21. Atmospheres  Asteroids, Moon, Mercury -- no atmosphere  Mars   Composition = 95 % CO 2, 3 % N (also water vapor, oxygen)  Venus:   Composition = 96 % CO 2, 4 % N (also sulfur compounds such as sulfuric acid, H 2 SO 4 )

22. Atmospheres (cont.)  Earth:   Composition = 77 % N, 21 % O 2 (also water vapor, CO 2, trace elements)  Why are the atmospheres of Venus, Mars and the Earth so different?  

23. The Carbonate-Silicate Cycle Water + CO 2 (rain) Ocean Carbonate + silicate (Sea floor rock) CO 2 Volcano Atmosphere Carbonate + water (stream) CO 2 + silicate (subvective melting)

24. CO 2 and Greenhouse Effect  Water washes CO 2 out of atmosphere where it is eventually deposited as rock   CO 2 is a greenhouse gas  

25. Carbonate-Silicate Feedback  Hot     cools off  Cool     heats up

26. CO 2 and the Inner Planets  Venus:  nearer the Sun so it is hotter   no way to get CO 2 out of atmosphere   Mars:   no way to get CO 2 out of rocks   Earth:  Carbonate-silicate cycle 

27. Summary  Inner or Terrestrial region  4 planets (Mercury, Venus, Earth, Mars)  1 large moon (The Moon)  thousands of asteroids  Information from 30 years of space missions  Size  Earth and Venus about the same  Mars, Mercury, the Moon, 1/2 -1/4 size of the Earth  Asteroids few km

28. Summary (cont.)  Composition  silicate rock crust  iron-silicate mantle  iron core  each planet has different proportions of each  Atmosphere  Mercury, Moon, asteroids -- none  Venus -- no water means CO 2 is in atmosphere  Mars -- no plate tectonics means CO 2 is in rocks  Earth -- carbonate-silicate cycle balances greenhouse effect