Origin of Our Solar System

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Origin of Our Solar System
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Earth and Space Science Earth in space and
time Objectives and Expectations
TEK Objective 5 Earth in space and time. The
student understands the solar nebular
accretionary disk model. The student is expected
to
analyze how gravitational condensation of solar
nebular gas and dust can lead to the accretion of
planetesimals and protoplanets
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Where did we come from?
The origin of the planets in our Solar System has
been debated since 1755 when Immanuel Kant
proposed the first theory
Scientists debated whether the origin of our
Solar System was usual, or a common consequence
of star formation
During the 1900s, many believed we are not a
unique occurrence because of the recent discovery
of other planetary systems around other stars
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Two Main Theories
The Nebular Hypothesis
The Protoplanet Hypothesis
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Nebula
Sun-like stars usually take around 100 million
years to form.
A nebula is the product of a supernova event. The
death of one system, may well be the birth of
another!
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The Nebular Hypothesis
In 1755 Immanuel Kant proposed that a solar
nebulae was pulled together by gravity so that it
collapsed into a flat, rotating disk that
eventually coalesced into the Sun and planets
Pierre Laplace expanded the theory in 1796 and
proposed that the planets were formed by rings of
matter split off a rotating nebulae by
centrifugal force
Solar nebulae are huge clouds of dust and gas
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The Nebular Hypothesis
Laplace stated that after the matter split off,
it coalesced into a planet. The process repeated
itself, resulting in a planet each time. The
matter left over was the Sun.
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Much like a figure skater. You may have noticed
that skaters can spin much faster if they pull
their arms closer to their bodies. The more
concentrated their body masses are, the faster
they'll be able to rotate.
The spinning nebula formed planets because as the
masses became more concentrated the more they
began to spin.
The hypothetical explosion squeezed the unformed
gas and dust together, which began to spin faster
and faster in a circle
As the sun formed in the middle, the cloud
started to flatten out into a disc, sort of like
a Frisbee or a pancake, with tiny dust grains
making up the rest of the disc.
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Problems With the Nebular Hypothesis
Used a flat, rotating nebula as the Solar
System's origin to explain why all the planets
orbit in nearly the same plane and in the same
direction
All planets revolve around the Sun in a
counterclockwise direction within a 7 band of
the equatorial region of the Sun, and nearly all
of them also turn on their individual axes in a
counterclockwise direction as well.
Contradicted the observation that the Sun
contains most of the Solar System's mass but only
a small fraction of its angular momentum.
Angular momentum is the measure of the tendency
of a rotating body to remain rotating
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Problems With the Nebular Hypothesis

• If rings of matter were split off, as Laplace
  stated, they wouldn't be pulled together to form
  planets but would disperse into space.

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Process of Nebular Accretion Disk Formation
Hypothesis

• Starts with Solar Nebulae
• Disturbance (possibly a Supernova) cause gradual
  collapse of Solar Nebulae
• Gravity causes cloud to shrink and compress the
  center which begins to heat up
• Accretion disk forms as matter spins around the
  center and forms a flat disk
• Thermal energy evaporates the disk

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Process of Nebular Nebular Accretion Disk
Formation Hypothesis

• Protostar forms with opaque core
• Energy is given off by protostar causing a
  cooling
• Cooling causes gas to condense into tiny specs of
  metal, rock, ice Stellar Debris
• Stellar Debris begins to stick together to form
  Planetesimals
• Accrection of Planetesimals forms Protoplanets
• Some Planetsimals will form into asteroids,
  comets, and moons

Protoplanet small body that could later form a
planet
Planetesimals- Baby Planets
Accretion gradual growth of planets by the
accumulation of other smaller bodies
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The Protoplanet Hypothesis
Because of faults in the nebular hypothesis,
other explanations of planet formation were
sought.
After many failures, such as the encounter
theory, astronomers returned to the nebular
hypothesis to find improvements during the mid
1900s.
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The Protoplanet Hypothesis
Formed independently by
Carl von Weizsacker
Gerard Kuiper
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The Protoplanet Hypothesis
The solar system begins to form as a rotating
cloud, or nebulae, collapses
Instabilities in the nebulae cause dust particles
to stick together and accrete into billions of
planetesimals with diameters of about 10 meters.
The planetesimals then collide and form
protoplanets. Meanwhile, the protosun in the
center of the nebular disk becomes massive and
hot enough to "turn on" by fusing hydrogen.
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The Sun begins to radiate energy and vaporize
dust in the inner part of the Solar System. The
remaining gas is blown away by solar winds.