Transcript 9terrestrial3s

The Terrestrial Planets
Astronomy 311
Professor Lee Carkner
Lecture 9
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

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
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:
Sources of Information for the
Inner Planets
Mercury:
Mariner 10 --
Venus:
Soviet Venera landers -Magellan --
Mars:
Viking, Pathfinder, Spirit, Opportunity -Viking, Global Surveyor, Odyssey --
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

Determining Planetary
Properties
Mass

Distance

Diameter

Determining Planetary
Properties (cont.)
Average Density

Atmospheric composition

The Planets That Weren’t
There should have been 2 other inner
planets
The Moon Impactor

The Asteroid Belt

The Moon and the Earth
The Moon
The Moon
First visited in 1959 by Luna 1 (USSR)

Moon facts
Diameter: 0.27
Mass: 0.01
Orbital Radius (from Earth): 0.003

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

Asteroids
Millions of small bodies orbit the Sun,
most between Mars and Jupiter (the
asteroid belt)

Meteors

Spacecraft

Asteroid Facts
Asteroids
Diameter: <0.14
Mass: <0.02
Orbital Radius: 2.8

Most have orbits within the asteroid
belt (~2-3.5 AU)
The Asteroid Gaspra
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)
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
Composition (cont.)
Earthquake studies indicate that the
Earth has a iron core


We believe that the other inner planets
have a similar structure

Interior Structure
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)
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?


The Carbonate-Silicate Cycle
Atmosphere
Water
+
CO2
(rain)
CO2
Volcano
CO2
+ silicate
(subvective
melting)
Ocean
Carbonate + silicate
(Sea floor rock)
Carbonate
+ water
(stream)
CO2 and Greenhouse Effect
Water washes CO2 out of atmosphere
where it is eventually deposited as rock

CO2 is a greenhouse gas


Carbonate-Silicate Feedback
Hot



cools off
Cool



heats up
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

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
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