Chapter 5: Formation of Stars and Planets (and more)

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Chapter 5 Formation of Stars and Planets (and
more) Part 2 - the Solar System
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EVERYTHING in the Solar System orbits the Sun!
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What is EVERYTHING?
The planets .
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and Pluto, too.
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Sun and planets to scale
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Kuiper Belt Objects - KBO
Minor/dwarf planets( --- Pluto ?)
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Pluto (and other Dwarf Planets)

• Much smaller than major planets
• Icy, comet-like composition
• Plutos main moon (Charon) is of similar size

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Pluto (and other Dwarf Planets)
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Oort Cloud
Left-overs from Solar System Formation Comets
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Our Solar System
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Oort Cloud
KBO
Solar System
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The Solar System consists of

1. Sun
2. Planets/Dwarf Planets
3. Moons
4. Asteroids
5. KBOs
6. Comets

The Solar System divided into

• 1. Terrestrial planets
• Jovian (gas giants) planets
• Asteroid Belt
• KBO
• Oort Cloud

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Solar system generalities

• All planets orbit and rotate on their axis in the
• same direction
• exceptions Venus, Uranus

Venus rotates opposite to its path around the Sun
(retrograde)
Uranus tilted about 90O
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Solar system generalities

• Small planets high density
• rich in iron and
  rock
• close to the Sun

• Large planets low density (gaseous)
• rich in hydrogen
  and ice
• far from the Sun

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Solar system generalities
4. Swarms of smaller bodies rocky asteroids

icy comets
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• The inner part of the protoplanetary disk is
  hotter than the outer part.
• The inner disk has only materials that do not
  melt at high temperatures.
• Refractory do not melt at high temperature.
• The outer disk has volatile materials like ices.
• Volatile can melt or evaporate at moderate
  temperatures.

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• The 4 inner planets (Mercury, Venus, Earth Mars)
  are rocky terrestrial planets.
• The 4 outer planets (Jupiter, Saturn, Uranus,
  Neptune) are gaseous giants.
• Asteroids, comets, and dwarf planets are leftover
  planetesimals.
• Moons formed from the giant planets accretion
  disks.

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The Formation of Planets
Why are there two major types of planets? How did
terrestrial planets form? How did jovian planets
form? What ended the era of planet formation?
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Inner parts of disk are hotter than outer
parts. Rock can be solid at much higher
temperatures than ice.
Inside the frost line Too hot for hydrogen
compounds to form ices. Outside the frost line
Cold enough for ices to form.
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Tiny solid particles stick to form
planetesimals. Gravity draws planetesimals
together to form planets. This process of
assembly is called planetesimal accretion
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PLANET FORMATION JOVIAN PLANET FORMATION
2 models core accretion
and gravitational collapse
(like stars)
IMPORTANT Jupiter had to form first to provide
protection for the inner
planets to form
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Gas giants must form before the solar nebula
dissipates (lt 10 million years)
Disks are seen around many young stars
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CORE ACCRETION GAS CAPTURE
planetesimals accrete into a solid core
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growing core attracts gas envelope
runaway gas accretion with a little solids
accretion ends when no more gas
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planet contracts and cools
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PLANET FORMATION TERRESTRIAL FORMATION
IMPORTANT Jupiter had to form first to provide
protection for the inner
planets to form
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CORE ACCRETION GAS CAPTURE
planetesimals accrete into a solid core
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• Many smaller objects collected into just a few
  large ones

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What ended the era of planet formation?
A combination of photons and the solar wind
outflowing matter from the Sunblew away the
leftover gases Magnetic fields in early solar
wind helped reduce Suns rotation rate
Post planet formation
Where did asteroids and comets come from? How do
we explain exceptions to the rules? How do we
explain the existence of our Moon? How old is the
solar system?
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Where did asteroids and comets come from?

• Leftovers from the accretion process
• Rocky asteroids inside frost line
• Icy comets outside frost line

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How do we explain exceptions to the rules?
Heavy Bombardment
Uranus odd tilt
Leftover planetesimals bombarded other objects in
the late stages of solar system formation
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Not really an exception but still interesting
What is the Origin of Earths Water
Water may have come to Earth by way of icy
planetesimals