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How did the Solar System form?
3. What are the broad general characteristics or
physical features of our Solar System and
how do they illuminate Solar System
formation?
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How did the Solar System form?
4. How did the terrestrial planets form and why
is the Solar System differentiated?
How did the Solar System form: Differentiation?
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How did the Solar System form: Differentiation?
•
The Solar System is differentiated. This means that it
is broken up into different parts, these parts are two
types of planets (and ice-rocky bodies). We need a
theory to account for this fact.
1.
2.
3.
Terrestrial-like or Inner Planets
Jovian-like or Gas Giants
Pluto-like bodies.
•
What Solar System feature separates these objects?
How did the Solar System form: Asteroids?
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• Asteroid = a rocky body
that likely originated
from the asteroid belt
and is < 1000 km
(although most are ~1
km) in diameter. They
are minor planets.
• They are the remains of
the formation of Earthlike planets.
How did the Solar System form: Asteroids?
• On January 1st 1801,
Giuseppe Piazzi
discovered an object
which he thought was a
new comet.
• Its orbit, however, was
more like a small planet.
• He named the object
Ceres, after the Sicilian
goddess of grain.
– Thus the first asteroid was
discovered.
How did the Solar System form: Asteroid Location?
How did the Solar System form: Asteroid Location?
• The asteroid belt is located between Mars
and Jupiter.
• It is approximately 2-3 AU from our star,
known as the Sun.
How did the Solar System form: Meteorites?
• Meteorites are pieces of
asteroids that travel
through our solar system
and land on Earth.
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• Before they land they are
termed meteors.
• They are rocks from
space!
How did …: Differentiated Meteorites?
• Iron meteorites – These are the cores of
minor planets.
– They are mainly
composed of Fe and Ni.
– They comprise 7% of all
the meteorites found on
Earth.
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How did …: Differentiated Meteorites?
• Stony-iron meteorites.
– These are the core-mantle
boundaries of minor
planets.
– Such rocks are composed
of Fe-Ni metal and
silicates, usually the
minerals olivine or
pyroxene.
– They compose 1% of all
the meteorites found on
this planet.
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How did …: Differentiated Meteorites?
• Achondrites (a type of Stony
meteorite).
– Such rocks are similar to
magma and lava on Earth.
They may have come from
mantle and crust areas of
minor planets.
– They may also be from other
planets such as Mars or from
the Moon.
– They compose 8% of all the
meteorites found on this
planet.
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How did …: Differentiated Bodies?
•
This is the process of becoming
different. A differentiated body
(planet, moon, asteroid, etc.) is
one that was heated internally
and melted. Upon heating
material then separates due to
differences in the density.
•
The Earth, Venus, Mars,
Mercury, Vesta, and the Moon
are examples of differentiated
bodies.
•
Thus, differentiated meteorites
have been through a planetarytype melting process.
How did the Solar System Form: Undifferentiated Meteorites?
• Chondrites (another type of
Stony meteorite).
– No rocks on Earth are in any
way like these rocks.
– They have not been through
a differentiation process.
They are undifferentiated.
– They compose 84% of all the
meteorites found on this
planet.
• They are fossils or the
physical remains of the
formation of Terrestrial
planets.
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How did… : What are the components of chondrites?
How did… : What are the components of chondrites?
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• Chondrules
• Calcium-rich,
aluminum-rich
inclusions
• Circumstellar grains
• Matrix
How did…: Why should you care about chondrites?
1. They are 4.556 billion years old.
2. They are the oldest rocks in our collection.
3. Tell the story of the earliest time of our solar
system’s formation. They should not exist by
accepted astrophysical models for solar
system formation.
4. Are what the Earth-like planets were made
from.
5. Contain mineral grains from other stars.
How did… : Chondrules
• Chondrules are the most abundant component
of chondrites.
• Chondros,  = grain or seed (Rose,
1864)
• Chondrules are mm to cm-size spherical
igneous rocks composed mainly of olivine,
pyroxene, and glass. They are igneous rocks,
rocks that have been melted in our nebula.
• They are the building blocks of Earth-like
planets.
How did… : Chondrules and Their Formation.
• Because chondrules are igneous, they were melted.
• Because they are not predicted to exist, it is critical to
determine what formed these objects.
• Because most meteorites are chondrites and thus most
asteroids are likely chondrites, processing was
extensive.
Thus some mechanism operated that processed rockforming materials by melting BEFORE the formation
of the terrestrial-like planets.
How did… : Chondrules and Their Formation.
• What mechanisms are hypothesized to produce
chondrules within our protoplanetary disk?
• Two general classes of hypotheses:
– I. Observed or known to have occurred
• 1. Link their formation to our YSO.
• 2. Collisions
– II. Hypothesized to have occurred
• 1. Nebular Shock Waves
• Some other process
How did the Solar System Form: Terrestrial Planets.
• The theory, as discussed by astronomy and
astrophysics, states that planets within the
inner solar system formed in three major
stages.
• Stage I
– 1. Dust grains acted as nuclei formation of matter,
or meter-sized rocks.
– 2. These meter-sized rocks accreted and collided to
form kilometer-sized rocks (asteroids).
– 3. These objects then formed planetesimals, small
moon-sized objects.
How did the Solar System Form: Terrestrial Planets.
• The theory, as discussed by geologists, states that
planets also formed in three major stages, but that
Stage I has four parts:
– 1. Dust grains acted as nuclei formation of millimeter-sized
dust-balls that were melted and produced chondrules and CAI.
– 2. Chondrules and CAIs then accreted to form meter-sized
objects.
– 3. Meter-sized objects then formed kilometer-sized objects.
– 4. Kilometer-sized objects then formed planetesimals.
– Melting and differentiation occurs here
How did the Solar System Form: Terrestrial Planets.
• Stage II:
– Planetesimals then collide and merge due to
gravitational forces between them. The total
number of these types of bodies decrease and
larger bodies known as protoplanets are
produced.
How did the Solar System Form: Terrestrial Planets.
• Stage III: The process of accretion of
planetesimals also leads to fragmentation
of bodies and heavy bombardment
occurs.
• The fragments are swept up by
protoplanets.
• These objects then become planets.
How did the Solar System Form: Terrestrial Planets.
• After accretion we are left with a solar
system. The condensation theory helps
account for the differentiation of the solar
system into terrestrial-like and Jovianlike planets.
• A major issue if not the major issue Temperature!
How did the Solar System Form: Jovian Planets.
• Formation of the Jovian or gas-giant planets is a little
less clear with a weaker consensus among scientists as
to a party-line theory.
– 1. These planets simply grew large or massive enough that
their gravitational fields pulled large masses of gas to their
“cores”.
– 2. They formed from instabilities in the cool outer regions of
the solar nebula, mimicking small scale nebular models.
– As of July 2003, this last hypothesis is given more weight.
How did the Solar System Form: No more gas and dust.
• Where did all the gas go?
– The major hypothesis states that gas, which
did not fall into the sun or form into planets,
was both blown off and reacted away by
solar winds and solar radiation during the
highly active stage of our star known as the
T Tauri phase.
How did the Solar System Form: No more gas and dust.
• Where did all the dust go?
– Simple, into the Sun or planets! Effective
processing.
An Important Point of Interpretation
•
Standard textbooks form Terrestrial planets
like this:
–
•
Dust to m-sized objects to km-sized objects to
Moon-sized objects to Planets!
But that’s wrong. Why? No chondrules!
–
Dust to mm-sized objects then zap then m-sized
objects, etc.
•
REMEMBER THIS POINT