Chapter 7 Our Solar System

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Chapter 7 Our Solar
System
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Guiding Questions

• Are all the other planets similar to Earth, or
  are they very different?
• What are the properties of the moons of other
  planets?
• How do we know what the other planets are made
  of?
• What is the difference between an asteroid and a
  comet?
• Why are some elements (like gold) quite rare,
  while others (like carbon) are more common?
• What are current theories about how the solar
  system formed?
• Did all of the planets form in the same way?
• What are the characteristics of extra-solar
  planets? How do we search for such planets?

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Contents of the Solar System

• One star, called Sun (more than half of stars
  mutliple!).
• The Sun has 1000x mass of all planets combined
• Eight planets (Pluto demoted to Kuiper belt
  object!)
• Over 100 moons orbiting the planets
• Hundreds of thousands of asteroids
• Countless comets
• Gas and dust

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The inner planets are quite close together while
the outer planets are separated by enormous
distances.
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The Sun is by far the largest thing in the solar
system. Most of the planets are quite small.
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There are two broad categories of planets
Earthlike and Jupiterlike.

• TERRESTRIAL
• Four inner planets.
• Orbit close to the Sun.
• Hard, rocky surfaces.
• Volcanoes, mountains, valleys.
• Very few moons.
• No rings.
• Terra is Earth in Latin.

• JOVIAN
• Four outermost planets (excluding Pluto).
• Many times larger than terrestrial planets.
• Separated by enormous distances.
• Primarily gaseous or liquid.
• Have many moons and complex ring systems.
• Jove was another name for the Roman god Jupiter.

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Seven large satellites (moons) are almost as big
as the terrestrial planets.
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Spectroscopy reveals the chemical composition of
the planets and moons.
Saturns Moon Titan has significant methane (CH4).
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Spectroscopy reveals the chemical composition of
the planets.
Jupiters moon Europa reflects sunlight exactly
like frozen water ice would do. This
demonstrates Europa is made of ice and not rock.
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Hydrogen and helium are abundant on the Jovian
planets, whereas the terrestrial planets are
composed mostly of heavy elements.

• Jupiters cloudtops are composed of mostly the
  lightest elements, hydrogen and helium.
• Hydrogen and helium are colorless the colors in
  the atmosphere are caused by trace amounts of
  other substances.

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Hydrogen and helium are abundant on the Jovian
planets, whereas the terrestrial planets are
composed mostly of heavy elements.

• Mars is composed mostly of heavy elements such as
  iron, silicon, magnesium, and sulfur.
• The Martian atmosphere, as seen in this Hubble
  Space Telescope image is thin and nearly
  cloudless. The large volcano on the left is
  Olympus Mons, nearly three times larger than
  Earths Mt. Everest.

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Small chunks of rock and ice also orbit the Sun.

• 433 Eros, only 33 km (21 mi.) across is one of
  hundreds of thousands of small asteroids, or
  minor planets, orbiting between the orbits of
  Mars and Jupiter.

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Small chunks of rock and ice also orbit the Sun.
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The relative abundances of the elements are the
result of cosmic processes.
For every 1012 atoms of hydrogen, there are only
6 atoms of gold.
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The relative abundances of the elements are the
result of cosmic processes.

• Hydrogen and helium are by far the most abundant.
• The next most abundant are
• Carbon, nitrogen, oxygen, neon, magnesium,
  silicon, sulfur, and iron.
• The final five elements to appear in meaningful
  amounts are
• Sodium, aluminum, argon, calcium, and nickel

These atoms that were in existence at the
beginning of the solar system are the same atoms
that are bodies are made of we are made of star
dust.
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The relative abundances of the elements are the
result of cosmic processes.
Atomic number is the number of protons in the
atoms nucleus.
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The Sun and planets formed from a vast, rotating
cloud called the solar nebula.

• The solar system started from a vast rotating
  cloud.
• The nebula contracted under its own gravity
  forming a dense protosun at the center.
• The gravitationally contracting cloud increased
  in temperature (Kelvin Helmholtz contraction).
• When hot enough in the center, nuclear reactions
  started in the core halting the contraction.

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The planets formed by the accretion of
planetesimals and the accumulation of gases in
the solar nebula.
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Planetesimals in the early solar system collide
and accrete to form protoplanets.
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In only 150 million years, the planets form with
heavy elements condensing in the warmer center
and the lighter elements condensing in the outer
reaches. This is the process of differentiation
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Solar System Evolution from Solar Nebula
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The planets formed by the accretion of
planetesimals and the accumulation of gases in
the solar nebula.
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The planets formed by the accretion of
planetesimals and the accumulation of gases in
the solar nebula.
Cosmic dust grains collected from the upper
atmosphere were plentiful in the early solar
system and they served as the building blocks of
the planets. (this grain is about 0.02 mm long)
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Chondrules found in Meteorites provide evidence
of prior molten state (heated)
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The young Sun experienced an intense, but brief
burst of energy that swept the solar system clean
of most planetary formation remains. Young stars
emitting these jets are called T Tauri stars.
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Astronomers have discovered planets orbiting
other stars.

• Large planets, like Jupiter, gravitationally pull
  on their central star causing the star to move in
  a small orbit about the center of mass.
• Planets orbiting other stars are called
  extrasolar planets.

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Astronomers have discovered planets orbiting
other stars.

• Even very large planets orbiting other stars can
  not be seen directly because the central star is
  far too bright.
• However, the small motions of an orbited star due
  to its gravitational attraction with an orbiting
  planet can sometimes be observed.

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Astronomers have discovered planets orbiting
other stars.

• Astronomers carefully measure the motion of a
  star with a planet orbiting it by looking at the
  starlight.
• Such a star has starlight that is alternately red
  shifted and blue shifted.
• To date, more than 100 extrasolar planets have
  been discovered using this method of looking for
  Doppler shifts.

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Chapter 7 Solar System Overview

• Are all the other planets similar to Earth, or
  are they very different?
• Two classes terrestrial (rocky), Jovian
  (gaseous)
• Do other planets have moons like Earths Moon?
• Yes, several are much larger, over 100 known
• What the other planets are made of?
• Terrestrial rocky (C, N, O, Si, Fe, NI)
  density 3x-6x water, Jovian gaseous (mostly H,
  He) , density 0.7x - 1.3x water
• What is the composition difference between an
  asteroid and a comet?
• Asteroids rocky, comet mostly water
• Why are some elements (like gold) quite rare,
  while others (like carbon) are more common?
• Fusion in core of a star forms light elements
  first, heavier elements (gt iron) only formed in
  supernovae (rare)
• What is current model of how the solar system
  formed?
• Coalesced from solar nebula (many seen in Orion
  star formation nebula today)
• Are there planets orbiting other stars? How do
  astronomers search for such planets?
• Yes, seen by planets effect on motion of parent
  star Doppler effect.

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Chapter 7 Definitions

• Accretion accumulation of material to form
  larger objects
• Differentiation Progression of densities in
  solar system from higher near the Sun to lower in
  outer solar system.
• Planetesimal small 1km rocky asteroid-like
  objects in early solar system
• Chondrules small, glassy, spherical particles in
  meteorites, indicative of prior molten state
• Kelvin-Helmholtz contraction conversion of
  graviational energy to heat on contraction
• T Tauri stars Very young stars, many with
  planetary systems still forming around them.