Solar System formed through the collapse of a large cloud o

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• Solar System Review

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Our Solar System - Origins

• Observations
• Ordered motions of objects
• Two types of planets Terrestrial vs. Jovian
• For example, Mars vs. Jupiter
• Asteroids and comets
• Exceptions to ordered motions
• Tilt of Earths axis, Earths Moon, Pluto

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Nebular Theory

• Solar System formed through the collapse of a
  large cloud of gas under its own gravity

Eagle Nebula
Lagoon Nebula
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Gravitational Collapse

• Start out with a large cloud of gas
• A few light years in size with a very low density
• Very cold temperatures
• Something triggers the collapse
• Supernova explosion
• Cloud can no longer support itself against its
  own gravity. Continues to collapse

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More Gravitational Collapse
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From Cloud to Solar System

• Energy Conservation
• Heats the cloud
• Ang. Momentum
• Causes the cloud to spin faster
• Cloud Flattens
• Mergers between particles average out the
  velocities

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Does this theory make sense?

• Observe many other stars forming from
  interstellar clouds with circumstellar disks

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How do planets form?

• Through accretion
• Small particles are able to build larger
  complexes of particles
• Eventually the complex becomes large enough to
  attract pieces through gravitation
  planetesimals
• Only the largest planetesimals survive to become
  planets

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Planet Formation

• Terrestrial planets (Mercury, Venus, Earth, and
  Mars) all formed beyond a distance of 0.3 AU
• Rock could not condense within this distance
• Jovian planets (Jupiter, Saturn, Uranus, and
  Neptune) all formed beyond the frost line (3.5
  AU)
• Hydrogen compounds formed the cores of these
  planets

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Jovian Planets

• Gravity of icy planetesimals was large enough to
  capture hydrogen and helium gas
• Continued to grow larger as mass increased
• Large masses also explain the large number of
  moons

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Other Solar Systems?

• Detected over 100 planets
• Can not detect directly
• Even for the largest planets, light from the star
  overwhelms any light from the planet
• Use indirect evidence to search for planets
• Gravitational tugs

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How old is the Solar System?

• Oldest Earth rocks found to be 4 billion years
  old
• But this only tells us the time since rock last
  solidified, after the Heavy Bombardment
• Solar System must be older than 4 billion years
• Moon rocks give an age of 4.4 billion years, but
  they also re-solidified at some point
• Need objects that have not vaporized since the
  solar nebular collapsed
• Meteorites!
• Found to have an age of 4.55 billion years

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The Inner Bodies
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Astronomy

• To the study of motion

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Interior Components

• The interiors of all the terrestrial bodies
  consist of the same components
• Core Highest density (iron, nickel)
• Mantle Rocky material, around core
• Crust Lowest density (granite,basalt)
• Material separated when Earth was still molten
• Densest material sank to the center

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Interior Structure
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Comparing Interiors
Active geology
Inactive geology
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Changing Appearances

• Before the Heavy Bombardment, the inner planets
  probably looked very similar, aside from size
• Today we can see they look very different, but
  why?
• Impacts Asteroids/Comets striking
• Volcanoes lava flows
• Tectonics Formation of mountains
• Erosion Wears down structures

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Craters

• Always circular in structure
• Produce a large amount of debris that litters the
  surrounding area
• Seen on all terrestrial planets

Left A bowl shaped crater Top Crater with a
central peak similar to dropping an object in
water
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Mercury

• Heavily cratered appearance
• 88 day orbit with a 59 day rotation rate (slow)
• Temp ranges between 425C and 150C
• No atmosphere
• Too close to the Sun
• Too small in size

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Activity on Mercury

• Very little if any Dead planet
• Lava plains, although no
• where near as large as
• those found on the moon
• Relatively few craters in
• Caloris Basin suggests volcanism after the
  Heavy Bombardment
• Little or no erosion

Caloris Basin
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Venus

• Sister Planet to Earth, but in fact is quite
  different
• Thick cloud cover prevents an optical view of the
  planet
• Use radar mapping by sending radio signals to
  see surface features
• Mostly rolling plains
• A few mountains

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Venus
Surface image from the Venera 13 spacecraft
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Volcanism on Venus

• Very few craters seen on Venus
• Due to a combination of plate tectonics and
  volcanism
• Few mountain ranges and deep trenches
• Large number of shield volcanoes

Sif Mons Shield Volcano
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Erosion on Venus

• Nearly non-existent
• No evidence of features eroding
• Extremely hot temperatures exceeding 430C
• Water/Ice cannot exist
• Very slow rotation rate of 243 days
• No wind of any sort

Ushas Mons
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Our Moon

• Only terrestrial planet with a large moon.
• Collision with a Mars sized object
• Moon has a similar composition to that of Earths
  surface
• Smaller proportion of vaporized materials (water)

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Our Moon

• Very similar in appearance to Mercury
• Much larger lava basins
• During differentiation, magma rose to the
  surface, creating magma oceans
• Must have a low viscosity due to their large size

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Mars
Recent image of Mars from NASAs Mars Exploration
Rover Spirit
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History of Mars
Percival Lowells drawings showing regions of
lush vegetation and canals to transport water
An actual image of Mars. As you can see, Lowell
had quite the imagination
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History of Mars

• One of the better studied planets. Multiple
  spacecraft have landed on Mars and taken images
  and data samples
• Vikings Missions (1976)
• Mars Pathfinder (1997)
• Spirit and Opportunity (2004)

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Impact Craters on Mars

• Shows numerous craters
• The northern
• hemisphere contains
• few craters and filled
• in with lava plains
• The southern
• hemisphere is at a
• higher elevation and
• contains many more craters

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Mars and Volcanoes

• Mars has the largest volcano in the solar system
• Volcanoes on Mars should be dead based on size
• Recent analysis finds volcanic rock at an age of
  only 180 million years!
• May become active again, but should die out
  within the next 1-2 billion years as the interior
  continues to cool

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Erosion on Mars

• The only other planet that shows significant
  erosion
• Wind/Dust Storms Rotation rate similar to
  Earths (1 day)
• Water Numerous images showing features believed
  to be created by running water

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Life on Mars?

• No Martians!
• Continuing to search for past life on Mars
• Best bet is to look for microbes
• Look ahead to future missions

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Asteroids and Comets
Hale-Bopp
Ida
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Asteroids

• Rocky leftover planetesimals
• Pieces that were not picked up by the inner
  planets
• Where are they?
• Most are in the Asteroid Belt between Mars and
  Jupiter
• Trojan Asteroids in Jupiters orbit
• Near Earth Objects (NEOs) those that are close
  to Earth

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Comets

• Icy leftovers
• Two locations
• Kuiper Belt
• Oort Cloud

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The Outer Solar System
Neptune
Orbital radii Jupiter 5.2 A.U. Saturn 9.5
A.U. Uranus 19 A.U. Neptune 30 A.U.
Uranus
Saturn
Jupiter
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Jupiter

• 11 times earths diameter (1/10 suns)
• 300 times earths mass (1/1000 suns mass)
• Visible surface is gas (mostly hydrogen)
  interior must be mostly liquid, with solid core
• Fascinating banded patterns, hurricanes, great
  red spot

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Moons of Jupiter

• Io volcanically active, covered with sulfur
• Europa Covered with ice, with liquid ocean
  underneath
• Ganymede Bigger than Mercury, icy and cratered
• Callisto Also big, icy, cratered
• Many smaller moons (chunks of rock)

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Io Heated by tidal friction
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Europa Water beneath ice
Water is probably kept warm by tidal friction.
Could this be a place to look for life?
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Moons of Jupiter
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Saturn

• Prettiest planet in small telescopes
• 9 times earths diameter
• 100 times earths mass (1/3 Jupiter)
• Gaseous surface, liquid interior, solid core
  (like Jupiter)
• Rings!
• Many moons

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Cassini Mission
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Saturns rings
Rings are mostly ice particles, from tiny grains
to boulder-sized chunks. Gaps are created by tug
of nearby moons.
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Titan (Saturns largest moon)
Opaque atmosphere of nitrogen, methane, smog.
Surface (cold!) could have liquid methane, other
hydrocarbons.
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Saturns other moons
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Uranus

• Discovered by William Herschel, 1781
• At the threshold of naked-eye visibility
• Less than half the size of Saturn, and nearly
  twice as far
• Another gas giant planet with rings (faint), many
  moons
• Spin axis is tipped sideways

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Uranus

• Discovered by William Herschel, 1781
• At the threshold of naked-eye visibility
• Less than half the size of Saturn, and nearly
  twice as far
• Another gas giant planet with rings (faint), many
  moons
• Spin axis is tipped sideways

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Moons of Uranus
All are icy, smaller than our own moon.
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Neptune

• Discovered by mathematics (anomaly in orbit of
  Uranus) in 1845-46.
• Can be seen in binoculars (looks like a faint
  star)
• About the same size as Uranus, but 60 farther
  away
• Voyager 2 discovered a cool blue spot, which has
  since disappeared
• Largest moon, Triton

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Pluto

• At 2300 km, Pluto is the smallest planet
• Has most elliptical orbit ranges from 4.4 to 7.4
  billion km from Sun (2.8-4.5 billion miles)
• Actually crosses orbit of Neptune closer to Sun
  than Neptune until 2009
• Orbits in 248 years, 1.5 times Neptune

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Pluto and Charon

• Plutos moon Charon is almost half as big as
  Pluto (1100 km)
• Orbits only 20,000 km away
• Pluto and Charon always keep same face to each
  other (rotation locked)
• Pluto rotates, and Charon revolves, in 6.4 days

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Properties of Pluto

• Discovered in 1930 by Clyde Tombaugh

Hubble ST image of Pluto Charon
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More on Plutos Moon

• Charon has about 1/8 the mass of Pluto
• Compared to our moon which has 1/80th the mass of
  Earth
• Charon also orbits at a small distance of only
  20,000 km
• Our moon orbits at 400,000 km

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Plutos Atmosphere

• A very thin atmosphere of nitrogen gasses
• Atmosphere is currently thinning as Pluto
  approaches aphelion
• Gas refreezes onto the surface
• Atmosphere will re-thicken when Pluto makes its
  way back to the Sun

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Future Pluto Mission

• Close-up images would improve upon our current
  knowledge of Plutos surface features
• Mission to Pluto (New Horizons) set to launch in
  2006 and reach Pluto/Charon in 2015

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The planets, to scale
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• A Closer Look at
• Our Solar System
• http//www.astro.umn.edu/courses/1001/prevsem/summ
  er104/lecnotes/256,1,Astronomy 1001
• http//departments.weber.edu/physics/schroeder/ast
  ro/lectureslides/352,9,The Outer Solar System
• http//www.uwgb.edu/dutchs/CosmosPowerPoint/277,18
  ,Pluto
• http//www.astro.umn.edu/courses/1001/prevsem/summ
  er204/lecnotes/256,1,Pluto and Earth