The Terrestrial Planets

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 Werent

• There should have been 2 other inner planets
• The Moon Impactor
• The Asteroid Belt

10
The Moon and the Earth
11
The Moon
12
The Moon

• 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 lt0.14
• Mass lt0.02
• 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/m3)
• 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 CO2, 3 N (also water vapor,
  oxygen)
• Venus
• Composition 96 CO2, 4 N (also sulfur
  compounds such as sulfuric acid, H2SO4)

22
Atmospheres (cont.)

• Earth
• Composition 77 N, 21 O2 (also water vapor,
  CO2, trace elements)
• Why are the atmospheres of Venus, Mars and the
  Earth so different?

23
The Carbonate-Silicate Cycle
Atmosphere
Water CO2 (rain)
CO2
Volcano
Ocean
CO2 silicate (subvective melting)
Carbonate water (stream)
Carbonate silicate (Sea floor rock)
24
CO2 and Greenhouse Effect

• Water washes CO2 out of atmosphere where it is
  eventually deposited as rock
• CO2 is a greenhouse gas

25
Carbonate-Silicate Feedback

• Hot
• cools off

• Cool
• heats up

26
CO2 and the Inner Planets

• Venus
• nearer the Sun so it is hotter
• no way to get CO2 out of atmosphere
• Mars
• no way to get CO2 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 CO2 is in atmosphere
• Mars -- no plate tectonics means CO2 is in rocks
• Earth -- carbonate-silicate cycle balances
  greenhouse effect