Announcements
• 7 people have still not joined the class on
Astronomy Place. Once you join, all your previous
submissions appear in your grade.
• Planet Assignment 5, due Wed. March 3,
– Astronomy Place tutorial “Surface Temperature of
Terrestrial Planets”
• Star Assignment 1, due Wed. March 3
– READ chapter 15, do Angel quiz
• Planet Project 6,
due Wednesday March 17
– Global Warming internet project
Announcement
• Wednesday
– Finish planets
– Begin the Sun, Read chapter 15
– If nice, view Moon, Stars & Planets from the
BPS roof
Earth’s Plate Motion
Objectives:
• Compare the Atmospheres of the terrestrial
planets. Describe and explain the differences
in composition & energy balance.
• Describe and explain the Greenhouse Effect.
Describe the processes contributing to global
warming of Earth.
• Describe how Earth’s climate is exceptional
compared to Mars & Venus.
• Describe the factors that effect long term
climate change.
Planets as Homes for Life
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
A tale of three planets
Thought Question
What does a planet need to support life?
Thought Question
What does a planet need to support life?
Write down your thoughts on the activity paper, along
with your full name & student ID. When you are
done pass them to the aisle for collection for credit.
What does a planet need to support
life?
•
•
•
•
Source of Energy
Elements - C, N, O, Ca, Fe, etc.
Liquid Water
Temperature
between freezing and boiling of water
Source of Energy
A Star (the Sun)
Elements
• 3rd generation Star or later
– Earlier generations produce the elements
heavier than H & He needed to form planets.
Recall: probability of planet formation
increases with increasing Iron abundance
– Elements such as C, N, O, Ca, Fe needed for
life, as we know it
Origin of water?
• Water in rocks, originally from
planetesimals, like icy comets formed far
from Sun
• Volcanoes OUTGAS Water (H2O) and
Carbon Dioxide (CO2) from rocks into the
atmosphere.
Volcano
How Much was Outgassed?
• Earth & Venus outgassed similar amounts of
H2O and CO2
– Can tell because have similar amounts of
Nitrogen today
• Mars, being smaller, probably outgassed
less.
How much was Lost?
• Mars, being smaller, although colder, lost
more atmosphere
• Venus & Earth large, lost little atmosphere
• Venus became very hot, water evaporated.
H2O molecules in atmosphere broken apart
by solar UV radiation, hydrogen easily
escaped.
Role of Planetary SIZE
Larger Planets heat more and cool slower
-> have thinner rigid lithospheres
-> more volcanic & tectonic activity
-> produce more atmosphere
More Massive Planets -> stronger gravity
-> more difficult for atmosphere to
escape.
-> retain more atmosphere
Terrestrial Planets
• Moon & Mercury - no atmosphere
– too small
• Venus : Earth : Mars = 90 : 1 : 0.01
– Why Earth so much less than Venus
• Venus & Mars, CO2 (98%)
• Earth, N2 (77%), O2 (21%)
– What happened to Earth’s CO2?
What happened to Earth’s CO2?
CO2
dissolves
in oceans
becomes
locked in
Rocks.
Venus has
no oceans.
What determines a planet’s
surface temperature?
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
743 K
(470 C)
(878 F)
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
223 K
(-50 C)
(-58 F)
288 K
( 15 C)
( 59 F)
Surface Temperature of Planets
Determined by balance between
- Heating by absorbing visible sunlight
and
- Cooling by radiating infrared light to space
Since Temperature does not change much, on average,
Amount of energy lost to space =
Amount of energy gained from Sun
The energy
emitted by a
planet in
infrared light
equals the
amount of
sunlight energy
it absorbs
Conservation
of energy
Heating by Absorbing Sunlight
Farther from the Sun -> less sunlight hits the planet
Sunlight spreads out
Heating by Absorbing Sunlight
Earth’s atmosphere reflects 1/3 of the sunlight
falling on it
More reflection -> Less Heating
Thought Question
What kind of shirt is cooler on a sunny summer
day?
A. White shirt
B. Black shirt
Heating by Absorbing Sunlight
Earth’s atmosphere absorbs most kinds of light
before it reaches the ground.
Cooling by Radiating Infrared Light
• Heat must leave Earth
• Surface Temperature of Earth ~ 300 K,
peak emission is in infrared
• Energy is conserved: Amount of heat
emitted = amount of heat absorbed or
temperature changes
Expert Model
Expert Model II
Simple Model
Carbon Dioxide Blanket
The hot temperatures may be due to a
buildup of carbon dioxide in the
atmosphere, caused by the burning of
fossil fuel, and by the shrinking of the
world's forests. Result: a blanket over the
planet that keeps in the heat. (Susan
Spencer, CBS News, 1999)
Why does Temperature Rise?
More insulation ->
Temperature rises to still get rid of the
same amount of heat
(Recall: Hotter -> Brighter)
Radiate more energy,
same fraction gets through,
= larger total amount escapes
No Greenhouse Temp
Actual Temp.
Warming
Venus
-43 C
470 C
513 C
Earth
-17 C
15 C
32 C
Moon
0C
Mars
-55 C
125 C (day)
-175 C (night)
-50 C
-5C
(from Table 11.2)
How is human activity
affecting Earth’s climate?
The Global Carbon Cycle - 1990s
Units Gt C and Gt C y-1
Atmosphere
…are leading to a
build up of CO2
in the atmosphere.
3.2
750
63
500 Plants
60
Soil
2000
6.3
Fossil Deposits
About
16,000
1.6
Fossil emissions ...
91.7
90
…and land clearing
in the tropics...
Oceans
39,000
The Causal Chain of Global
Warming
Burning Fossil Fuels
CO2 Buildup
CO2 Traps Heat = Insulates
Temperature Rises
Negative Consequences
CO2
Concentration
Indicators of the Human Influence
on the Atmosphere during the Industrial Era
Global Warming
Increased CO2 is
causing global
warming
What can and should we do?
We are responsible for managing
our Earth prudently!
Confusions
• Originally, surfaces were heated by
bombardment, interiors by differentiation
and radioactive decay. Now surface is
heated by sunlight.
• More craters on small planets because their
lithosphere became solid quickly, while
heavy bombardment was still occurring.
Confusions
• Force of gravity is proportional to both
masses, so objects with less mass feel a
smaller force.
• Atmosphere’s pressure is due to its particles
colliding. When put more molecules in a
balloon there are more particles to collide ->
more pressure.
Global Warming Project
due Wednesday March 17
• Sample 4 web sites taking different
positions on whether Global Warming is
occurring & whether people are responsible.
• For each site, evaluate the science - Is it
good or poor?
• Criteria?