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

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QuickTime™ and aTIFF (Uncompressed) decompressor

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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 oceansbecomes locked inRocks.

Venus hasno oceans.

What determines a planet’s surface temperature?

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743 K (470 C)(878 F)

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 shirtB. Black shirt

Earth’s atmosphere absorbs most kinds of light before it reaches the ground.

Heating by Absorbing Sunlight

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 0 C 125 C (day) ---175 C (night)

Mars -55 C -50 C 5 C

(from Table 11.2)

How is human activity affecting Earth’s climate?

The Global Carbon Cycle - 1990sUnits Gt C and Gt C y-1

Atmosphere

Fossil Deposits6.363

91.7

60

90

3.2

Plants

Soil

Oceans

750

500

2000

39,000

About 16,0001.6

…are leading to a build up of CO2

in the atmosphere.

Fossil emissions ...

…and land clearing in the tropics...

Burning Fossil FuelsCO2 BuildupCO2 Traps Heat = InsulatesTemperature RisesNegative Consequences

The Causal Chain of Global Warming

CO2 Concen-tration

Indicators of the Human Influenceon the Atmosphere during the Industrial Era

Increased CO2 is causing global warming

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 Projectdue 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?