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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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Announcements
• Next Midterm 10/29
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Last Class
• Moon??
• Mercury
• Venus
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
This Class
• Brief Backtrack
• SS Formation
• Earth in brief
• LT Greenhouse Effect
• Climate Change
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Formation of the Solar System
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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!
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Neil Degrasse Tyson “The most astounding fact”
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Solar System Formation
• Start with interstellar cloud
• “enriched” with heavy elements
• Starts to break up into clumps
NASA, C.R. O'Dell
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Solar System Formation
• Clump collapses
• Forms protoplanetary disk
• Center collapses, heats up, forms Sun
• Disk fragments, forms planets
• “Debris” gets cleared
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Protostar becomes a normal Star
• Star stabilizes with pressure and gravity in balance
• Planets form out of the disk
FORMATION OF PLANETS
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Dr. Tyson, we meet again!
• http://www.pbs.org/wgbh/nova/space/origins-solar-system.html
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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!
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Barringer Crater, AZ
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Manicouagan Crater, Canada
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Northern Chad
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Copernicus Crater, Moon
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Victoria Crater, Mars
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
The Earth as a Planet
The Earth as a Planet
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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?)
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Earth’s Structure
• Core — Hot as the Sun’s surface (~6000 K) & dense
• Solid iron inner core
• liquid iron core surrounding it
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Magnetic Field via Dynamo Effect
• 2 Key components
• Liquid conductor
• Rotation
image from: http://www.abc.net.au
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Earth’s Magnetic Field
LET’S PRACTICE
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
History of Geological Activity
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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”
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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!
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Greenhouse Effect
Astronomy 1 - Elementary Astronomy LA Mission College Levine 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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Greenhouse Gasses
• Carbon dioxide & other gasses
• transparent to visible light
• absorb IR light
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
TED Talk, Jun 2009
WRAP-UP
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Topic for Next Class
• Mars
• Jupiter & moons
• Saturn & moons
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Reading Assignment
• Astro: 7
• Astropedia: 8
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Homework
• No new HW yet