Download Intro to Solar System

Origin of the Solar System
and Solar System Debris
Intro to Solar System
Origins of the Solar System
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Debris
• comets
• meteoroids
• asteroids
• gas
• dust
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Origins of the Solar System
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Asteroids
irregular, rocky hunks
small in mass and size
Ceres - largest, 1000 km in diameter
(1/3 Moon)
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Asteroid Belt
2.8 AU from the Sun, between Mars
and Jupiter
some with highly eccentric orbits, e.g.
Icarus, goes inside the orbit of
Mercury
5500 asteroids discovered so far
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A Typical Asteroid
fluctuates in brightness
=> tumbling, irregular in shape
cratered surfaces, often rough and pitted
lose chunks in collisions
Toutatis - two orbiting each other
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Categories of Asteroids
• S type (stony)
relatively bright
stony silicate materials
• C type (carbon)
darker
contains carbon compounds
• M type (metallic)
brighter than C, darker than S
metallic substances
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Comets - Heralds of Disaster
first seen as a bright blob
later grows brighter and
sprouts a tail as it nears
the Sun
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Comets
coma:
bright head of the comet
may reach a million km diameter
nucleus: small central core, about 10 km
tail:
material in the comet is heated
by the Sun and vaporizes, can
be millions of km’s long
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Two Tails!
gas tail:
ion tail
emission lines
ionized gas
plasma
carbon monoxide (CO)
carbon dioxide (CO2)
molecular nitrogen (N2)
magnetic fields interact with plasma
giving the comet a glow
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dust tail: spectrum of sunlight
reflected by the dust
radiation pressure pushes dust
out of the coma
points downward from the ion tail
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Dirty Snowball Model
Nucleus: solid, compact body
frozen ices (water, methane,
ammonia) embedded in
rocky material
Coma:
nears the Sun, icy material
vaporizes, forming the coma
Tail:
continual vaporizing enlarges
the coma and forms the tail
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Periodic Comets
• make regular passes near the Sun
• follow Kepler’s Laws
• have elliptical orbits
short period:
orbit in same directions
as the planets, less eccentric
long period:
highly eccentric orbits, cut
through plane of Solar System
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Oort Cloud
a reservoir of comets out beyond Pluto,
beyond the Kuiper Belt (belt of icy objects)
average semi-major axis is 50,000 AU,
period of 10 million years,
eccentricity close to 1
travel very slowly, spend a lot of time
far out in their orbits
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Origins of the Solar System
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Wonder of It All
How did they get out there in the first place?
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Origins of the Solar System
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Meteors and Meteoroids
meteoroid:
name for particles and such
before entering Earth’s
atmosphere
meteor:
solid particle that vaporizes
in Earth’s atmosphere
meteorite:
particles large enough to
survive and land on Earth
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Origins of Meteoroids
• dust and ice flaked from comets
• 99% comes from comets
• follow orbits of original comets
meteor showers: many meteors in a short
period of time
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Types of Meteoroids
• irons
• stones
90% iron, 9% nickel
high density, melted appearance
low density silicates similar to
Earth’s crust
chondrules - silicate spheres
carbonaceous chondrites:
chondrules embedded in material
containing a lot of carbon
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• stony iron:
crossbreed between
stones and irons
meteorites - come from asteroids rather
than from comets
have enough density to make it
through our atmosphere
Identify a meteorite: etch a polished surface
with acid and look for Widmanstatten figures
They were originally inside a larger
body and could cool slowly.
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Origins of the Solar System
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C type asteroid
carbonaceous
chondrite
S type asteroid
stony meteorite
M type asteroid
iron meteorites
probable that the parent bodies were first
things to form in the Solar System - ages
will directly indicate the age of Solar System
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Solar System
Chemically:
Sun
mostly gaseous with some
icy/rocky material as gases
Terrestrial planets & asteroids
rocky, metallic
Jupiter, Saturn
mostly gaseous
Uranus, Neptune, Pluto, Charon, comets
mostly icy
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Dynamically
• planets revolve counterclockwise
Sun rotates counterclockwise
• major planets have orbits only slightly
inclined with plane of Sun
exceptions: Pluto and Mercury
• planets move in orbits that are nearly
circular (low eccentricity)
exceptions: Pluto, Mercury
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• planets rotate counterclockwise (same
direction as orbital motion
exception: Venus, Uranus, Pluto
• planets’ orbital distances follow a regular
spacing (sort of) - about twice as one before
• most satellites revolve in same direction
as parent planet rotates and lie close to
equatorial plane
• some satellites’ orbital distance follows a
regular spacing rule
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• planets together contain more angular
momentum than the Sun (99.5% vs 0.5%)
• long period comets - come in from all
angles and directions
short period comets, planets, satellites,
asteroids - coplanar orbits
• all Jovian planets have rings
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Nebular Model
Sun and planets form from a cloud of
interstellar material
Sun forms in the center of flattened cloud
Planets grow from the disk of the cloud
Solar System is basically flat with the Sun
in the middle.
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Conservation of Angular Momentum
once something starts spinning, it will continue
unless acted on by an external influence
angular momentum: tendency to keep spinning
angular momentum depends on the mass
and on how that mass is spread out
Any time a body contracts (gets smaller),
it spins faster in order to conserve angular
momentum.
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Imagine, a large cloud of gas and dust,
slowly spinning.
It starts to shrink, pulling in on itself
with its own gravity.
What happens?
It spins even faster !!
And eventually it collapses along the
rotation axis.
a flat disk with a fat center !
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Nice model …….. one problem …...
Angular momentum is not as expected.
Sun
Planets
99% mass
1% mass
1% ang. momentum
99% ang. momentum
Sun should be spinning very rapidly!
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gravitational contraction:
a mass pulling itself together gets hotter
gravitational potential energy
kinetic energy (heat energy)
As the cloud contracts, it gets hotter.
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Stages of Evolution
• formation of nebula out of which the
planets and Sun originate
• formation of original planetary debris
• evolution of planets
• dissipation of leftover gas and dust
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Planetary Formation
• grains collide & accrete to form larger,
pebble-sized objects
• pebbles accumulate into planetesimals
by gravitational contraction
composed of whatever is handy
• planetesimals gather into larger bodies
takes tens of thousands of years
clear out a space in the nebula
• protoplants - process takes 100 million
years
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Condensation Sequence
• temperature determines what materials
condense
• below 2000 K, grains of terrestrial
material condense
• below 273 K, grains of terrestrial and icy
materials condense
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Different distances from the Sun,
different temperatures allow different
materials to condense and form into grains.
How LOW the temperature gets
determines what materials.
Leftover planetesimals bombard the new
planets’ surfaces causing craters.
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Planets become differentiated.
Some rocky, metallic planetesimals end up
as asteroids. Icy ones become comet nuclei.
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