Transcript 9terrestrial5s

The Terrestrial Planets
Astronomy 311
Professor Lee Carkner
Lecture 9
Early Missions to the Inner Planets
1962 -- Mariner 2
Venus Fly-by

1973 Mariner 10
Venus/Mercury Fly-by

1964 -- Mariner 4
Mars Fly-by

1970 Venera 7
Venus lander
first successful
landing on another
planet
1975 Viking 1 and 2
Mars lander
first successful landing on
Mars
Planetary Missions
First wave of exploration from 1960-1979

Very large number of Soviet missions, most were
failures
Venus: 15 successes, 31 missions


Smaller number of US missions, but higher
success rate
Mercury: 2 successes, 2 mission
Venus: 6 successes, 7 missions

We are now starting to see other countries get
more involved with space exploration
Most notably Japan and The European Union
Sources of Information for the
Inner Planets
Mercury:
Mariner 10 and MESSENGER --
Venus:
Soviet Venera landers -- surface conditions
Magellan --
Mars:
Viking, Pathfinder, Spirit, Opportunity -Viking, Global Surveyor, Odyssey, Recon
Orbiter -- maps of the surface
Inner Planet Facts
Mercury
Diameter: 0.38
Mass: 0.06
Orbital Radius: 0.4
Venus
Diameter: 0.95
Mass: 0.82
Orbital Radius: 0.7
Earth
Diameter: 1
Mass: 1
Orbital Radius: 1
Mars
Diameter: 0.53
Mass: 0.11
Orbital Radius: 1.5
Determining Planetary
Properties
Mass


Distance
Can find directly with radar
Diameter
Can get from the angular diameter and the
distance
Determining Planetary
Properties (cont.)
Average Density

Atmospheric composition
take a spectrum of the atmosphere, look
for the spectral signature of elements
Scale Models
We want to make a scale model to try to
understand astronomical distances
Need to find the scale
scale = (real size) / (model size)
example: miles per inch or light years per cm
Once you have the scale you can find the
model size for any real object
(model size) = (real size) / scale
The Planets That Weren’t
There should have been 2 other inner
planets

A planet about the size of Mars may have
hit the Earth a few billion years ago, the
debris formed into the Moon

Jupiter’s gravity disrupted the
planetesimals between Mars and Jupiter so
they never formed a planet
The Moon

Most of our information comes from the 6
Apollo landings (11-17, excluding 13)
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
It is difficult to gravitationally capture
something
Asteroids
Millions of small bodies orbit the Sun,
most between Mars and Jupiter (the
asteroid belt)
Our information comes from 2 sources:

Pieces of asteroids that have fallen to Earth

For example:
NEAR orbiting Eros
Hayabusa landing on Itokawa
Asteroid Facts
Asteroids
Diameter: <0.08
Mass: <0.0002
Orbital Radius: 2.8

Most have orbits within the asteroid
belt (~2-3.5 AU)
Sizes of the Inner Planets
Sizes relative to Earth
Earth: 1 (diameter = 13,000 km)
Venus: 0.95
Mars: 0.53
Mercury: 0.38
Moon: 0.27
Asteroid: <0.08
All are small compared to the gas giants
(Neptune is ~4 times the diameter of the
Earth and ~64 times the volume)
Atmospheres

Mars
Surface pressure =
Composition = 95 % CO2, 3 % N (also
water vapor, oxygen)
Venus:
 Surface pressure =
Composition = 96 % CO2, 4 % N (also
sulfur compounds such as sulfuric acid,
H2SO4)
Atmospheres (cont.)
Earth:
Surface pressure =
Composition = 77 % N, 21 % O2 (also water vapor,
CO2, trace elements)
Why are the atmospheres of Venus, Mars and
the Earth so different?

The Earth can regulate its atmosphere through
the carbonate-silicate cycle, the other planets
cannot
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

More CO2 = higher temperature
Carbonate-Silicate Feedback
Hot

Cool

more CO2 washes out

cools off
less CO2 washes out

heats up
CO2 and the Inner Planets
Venus:

all the water boiled off and was disassociated

thick CO2 atmosphere and high temperatures
Mars:

no way to get CO2 out of rocks
thin CO2 atmosphere and low temperatures
Earth:

mild temperature and atmosphere
Composition

Density of rock (silicates) ~3000 kg/m3
What makes up the difference?
Iron


“Rocky” planets could also be called the “metal”
planets
Interior Structure
Composition (cont.)
Earthquake studies indicate that the
Earth has a iron core

Earth has a density gradient, heavier
materials near the center, lighter near the
surface
We believe that the other inner planets
have a similar structure

Next Time
Read Chapter 8
but just the Mercury parts
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