earth, ss formation, greenhouse f2015... · earth, ss formation, greenhouse. astronomy 1 -...

Astronomy 1 — Elementary Astronomy LA Mission College

Spring F2015

Earth, SS Formation, Greenhouse

Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015

Cartoon of the Day

“And part of the soil is called to wash away

In storms and streams shave close and gnaw the rocks.

Besides, whatever the earth feeds and grows

Is restored to earth. And since she surely is

The womb of all things and their common grave,

Earth must dwindle, you see and take on growth again.”

— Titus Lucretius

Announcements

• Next Midterm 10/29

Last Class

• Moon??

• Mercury

• Venus

This Class

• Brief Backtrack

• SS Formation

• Earth in brief

• LT Greenhouse Effect

• Climate Change

Spring F2015

Formation of the Solar System

Solar Nebula Theory

• Planets form @ same time from same cloud as Sun.

• ~ 4.6 billion years ago

• Basis of modern theory of exo- planetary system formation

STAR FORMATION A SUN IS BORN

First You need Raw Materials

• Big Bang • H and He

• Massive stars + supernovae • everything else

• “We are all made of star-stuff” -- Carl Sagan

• Think about it!

Neil Degrasse Tyson “The most astounding fact”

Need a way to reproduce:

• Disk shape, dominant co-rotation/revolution

• 2 types of planets

• Space “Debris”: Asteroids, comets, meteoroids

• Lots of empty space

• Common age ~4.6 billion years

Solar System Formation

• Start with interstellar cloud

• “enriched” with heavy elements

• Starts to break up into clumps

NASA, C.R. O'Dell

Solar System Formation

• Clump collapses

• Forms protoplanetary disk

• Center collapses, heats up, forms Sun

• Disk fragments, forms planets

• “Debris” gets cleared

Protostar becomes a normal Star

• Star stabilizes with pressure and gravity in balance

• Planets form out of the disk

FORMATION OF PLANETS

Protoplanetary Disk

• The inner part of the disk is hotter than the outer part.

• at the “frost line” water can exist as ice (~2.7 AU)

• Terrestrial planets form inside the frost line by accretion

• Jovian planets form outside the frost line by collapse

Dr. Tyson, we meet again!

• http://www.pbs.org/wgbh/nova/space/origins-solar-system.html

Differentiation -- Structuring Planets

• Differentiation— the separation of material by density

• dense (iron, nickel) stuff sinks to the bottom

• less dense stuff (carbon, oxygen) remains on top

Differentiation -- Structuring Planets

• Homogeneous (same composition all through) protoplanets form

• densest materials move to center (core)

• Least dense materials remain at surface (crust)

• Both terrestrial and jovian planets wind up structured

• densest at center, lightest at top

LET’S PRACTICE

Where did most of the elements in the Solar System come from?

A. They were made in the Sun

B. They were manufactured during the Big Bang

C. They came from previous generations of stars

D. They have always existed

Which of the following pairs of planets formed at a location above the freezing temperature of water?

A. Jupiter and Saturn

B. Mars and Jupiter

C. Earth and Mars

D. Mercury and Saturn

E. Venus and Jupiter

GRAVITY, COLLISIONS & CRATERING

Disk Clearing and Heavy Bombardment

• SS is mostly empty space now

• Four mechanisms:

• solar radiation (photons)

• solar wind (particles)

• gravitational attraction to planets (particularly the Jovian planets)

• ejection (gravitational) by the planets (era of heavy bombardment)

• Lots of cratering!

Barringer Crater, AZ

Manicouagan Crater, Canada

Northern Chad

Copernicus Crater, Moon

Victoria Crater, Mars

Crater Counting

• Estimate relative age of surfaces

• For moon, compared to sample dating

• Lightly cratered surfaces younger than heavily cratered surfaces.

Heavily cratered surface of Saturn’s moon Rhea, taken by Cassini spacecraft

Lightly cratered surface of Saturn’s moon Enceladus, taken by Cassini spacecraft

LET’S PRACTICE

The following exist as a ubiquitous signature of the clearing of the solar system.

A. cratering

B. planets

C. comets

D. none of the above

If you observe a rocky moon with areas that have many craters and areas are very smooth, you could conclude ___.

A. The smooth areas are “younger” than the cratered areas.

B. The moon formed fairly early in the history of the solar system.

C. A process like volcanism has resurfaced areas on the moon.

D. All of these

E. None of these

Spring F2015

The Earth as a Planet

The “Habitable Zone”

• In astronomy and astrobiology, the habitable zone is the region around a star where a planet with sufficient atmospheric pressure can maintain liquid water on its surface.

www.astrobio.net

Earth’s Uniqueness

• Earth demonstrates every process seen on terrestrial worlds

• Unique in 2 important ways

• Surface water (75% of the surface is water)

• No other SS body has surface water currently

• Life

• No other SS body has been found to have life. Yet.

Tectonic Activity

• Planetary heat is transferred to the surface as geological activity

• the energy of formation of the planet

• heat generated by the decay of radioactive elements.

• Higher mass →more heat → tectonic activity.

• Types of tectonic activity

• Volcanism

• mountain/terrain formation

• crustal fractures

• plate motion (Earth only?)

Earth’s Structure

• Core — Hot as the Sun’s surface (~6000 K) & dense

• Solid iron inner core

• liquid iron core surrounding it

Earth’s Structure — Mantle

• Mantle

• Solid (“plastic”)

• Crust

• Thicker under land (60 km)

• thinner under oceans (10 km)

• Brittle: Broken into tectonic plates

EARTH’S MAGNETIC FIELD

Earth’s Magnetic Field

• Protects us from the solar wind • which would otherwise slowly strip the Earth’s atmosphere away...which would

NOT be good!

• Is generated by the dynamo effect

Magnetic Field via Dynamo Effect

• 2 Key components

• Liquid conductor

• Rotation

image from: http://www.abc.net.au

Earth’s Magnetic Field

LET’S PRACTICE

If the Earth’s rotation were to slow down drastically which of the following would happen?

A. Runaway Greenhouse effect, leading to unsurvivable surface temperatures

B. Diminishment of Earth’s magnetic field, leading to loss of protection from the solar wind

C. Diminishment of atmospheric friction, leading to dramatic cooling of the surface

D. Diminishment of gravitational force, leading to loss of the Moon.

EARTH’S TIMELINE

History of Geological Activity

Earth’s Atmosphere

• 76% Nitrogen, 23% Oxygen (together 99%)

• 0.06-1.7% water vapor

• 0.05% carbon dioxide CO2

• Ozone (O3) protects the surface from UV radiation

• CO2 is a “greenhouse gas”

Evolution of Atmosphere

• Primordial Atmosphere

• outgassed by geologic activity (volcanoes) ~4 billion years ago

• carbon dioxide (CO2), nitrogen, water vapor

• CO2 levels decreased

• Earth cooled, water vapor condensed

• Oceans formed!

• Water absorbed CO2 — carbonation

Evolution of Atmosphere

• O2 levels increased

• The rise of oxygen levels in the Earth’s atmosphere is tied to life.

• Specifically photosynthesis

• evolved 2.7 - 2.4 billion years ago

• picked up when the oceans developed plant life 2-2.5 billion years ago

• Oxygen exists because of life, not vice versa!

Spring F2015

Greenhouse Effect

• Glass:

• transparent to visible light

• opaque to IR light

• Greenhouse

• visible light enters through glass

• warms ground & air

• ground & air give off IR

• IR can’t exit through glass

• Greenhouse gets warmer than outside

Greenhouse Gasses

• Carbon dioxide & other gasses

• transparent to visible light

• absorb IR light

Greenhouse Effect

• Sunlight energy comes in mostly as visible light

• Warms atmosphere & ground which emit IR

• IR light is absorbed by greenhouse gasses in the atmosphere

• “recycles” some of the energy — warms earth

Greenhouse Effect

• More greenhouse gasses, more recycled energy

• Some natural/necessary to keep Earth comfortably warm

• Venus has a thick carbon dioxide atmosphere — VERY HOT

WARMUP QUESTION

Which of the following is part of the Earth’s natural greenhouse effect?

A. Earth’s atmosphere continually becomes thicker with greenhouse gases.

B. Infrared light becomes permanently trapped in our atmosphere by greenhouse gases.

C. The ozone hole causes significant increases in surface temperature.

D. Earth’s surface and atmospheric gases absorb energy and then give off infrared light.

E. Heat is transferred in the atmosphere through the circulation of greenhouse gases.

LECTURE-TUTORIAL GREENHOUSE EFFECT

Which of the following is part of the Earth’s natural greenhouse effect?

A. Earth’s atmosphere continually becomes thicker with greenhouse gases.

B. Infrared light becomes permanently trapped in our atmosphere by greenhouse gases.

C. The ozone hole causes significant increases in surface temperature.

D. Earth’s surface and atmospheric gases absorb energy and then give off infrared light.

E. Heat is transferred in the atmosphere through the circulation of greenhouse gases.

Let’s Practice

If Earth’s atmosphere were able to completely absorb visible light, which of the following would be true?

A. The Earth’s surface temperature would be cooler than it is today.

B. The Earth’s surface temperature would be warmer than it is today.

C. The Earth’s surface temperature would be the same temperature as it is today.

D. There is not enough information to answer this question.

HUMANS AND CLIMATE CHANGE

Greenhouse Effect

• Is a natural process

• Essential to maintain Earth’s temperature

• HOWEVER

• Human activity has dramatically increased the level of greenhouse gasses

• Esp. via the internal combustion engine

Global Warming

• Beyond any reasonable doubt, the average temperature on Earth is increasing.

• loss of glaciers & polar ice caps

• rising sea water levels

• global climate change

NASA Goddard Institute for Space Studies

ICE MELT

TED Talk, Jun 2009

WRAP-UP

Topic for Next Class

• Mars

• Jupiter & moons

• Saturn & moons

Reading Assignment

• Astro: 7

• Astropedia: 8

Homework

• No new HW yet

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