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

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 (H 2 O) and Carbon Dioxide (CO 2 ) from rocks into the atmosphere.

Volcano

How Much was Outgassed? Earth & Venus outgassed similar amounts of H 2 O and CO 2 –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. H 2 O 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, CO 2 (98%) Earth, N 2 (77%), O 2 (21%) –What happened to Earth’s CO 2 ?

What happened to Earth’s CO 2 ? CO 2 dissolves in oceans becomes locked in Rocks. Venus has no oceans.

What determines a planet’s surface temperature?

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

No Greenhouse Reflectivity Temp Actual Temp. Venus72%-43 C 470 C Earth36%-17 C 15 C Moon 7% 0 C 125 C (day) -175 C (night) Mars25%-55 C -50 C (from Table 11.2)

Thought Question What kind of shirt is cooler on a sunny summer day? A. White shirt B. 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) 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 s Units Gt C and Gt C y -1 Atmosphere Fossil Deposits Plants Soil Oceans ,000 About 16, …are leading to a build up of CO 2 in the atmosphere. Fossil emissions... …and land clearing in the tropics...

Burning Fossil Fuels CO 2 Buildup CO 2 Traps Heat = Insulates Temperature Rises Negative Consequences The Causal Chain of Global Warming

CO 2 Concen- tration

Indicators of the Human Influence on the Atmosphere during the Industrial Era

Increased CO 2 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 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?