Chapter 7 Our Planetary System

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Chapter 7Our Planetary System
Earth, as viewed by the Voyager spacecraft
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7.1 Studying the Solar System

• Our goals for learning
• What does the solar system look like?
• What can we learn by comparing the planets to one
  another?
• What are the major features of the Sun and
  planets?

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What does the solar system look like?
1. What is in it?
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• Eight major planets with nearly circular orbits
• Pluto (dwarf planet) is smaller than the major
  planets and has a more elliptical orbit

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What Counts as a Planet?

• The IAU definition of a planet (2006)
• is in orbit around the Sun,
• has sufficient mass so that it is nearly round
• has "cleared the neighborhood" around its orbit.

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History of Planet Count

• The number of objects counted as planets in the
  solar system has varied over the centuries
• As low as 6 and has high as 13

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What does the solar system look like?
2. How far apart . are things? Planets are
very tiny compared to distances between them.
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What can we learn by comparing the planets to one
another?
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Comparative Planetology

• We can learn more about a world like our Earth by
  studying in context with other worlds in the
  solar system.
• Stay focused on processes common to multiple
  worlds instead of individual facts specific to a
  particular world.

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• Comparing the planets reveals patterns among them
• Those patterns provide insights that help us
  understand our own planet

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What are the major features of the Sun and
planets?
Sun and planets to scale
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Density and Composition
Density mass _ volume
g/cm3

• Measure a planets volume
• Measure a planets spin gt calculate mass
• Result is a worlds bulk density.

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Density and Composition

• Common materials
• Iron 7.9 g/cm3
• Basalt 3.3 g/cm3
• (rock)
• Carbon and hydrogen ices 0.4-1.5 g/cm3
• (volatiles)
• H and He ltlt0.01 g/cm3

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Density and Composition

• Earth 5.5 g/cm3 composition- iron, rock
• Saturn 0.7 g/cm3 composition- some rock,
  volatiles and lots HHe
• Callisto 1.9 g/cm3 Titan 2 g/cm3 composition
  -rock and ice

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Thought Question

• Planet Mars has a bulk density of 3.9 g/cm3 What
  materials is it made of ?
• Iron 7.9 g/cm3
• Basalt 3.3 g/cm3
• Volatiles 1-1.5 g/cm3
• H and He ltlt0.01 g/cm3

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Thought Question

• Planet Mars has a bulk density of 3.9 g/cm3 What
  materials is it made of ?
• Iron 7.9 g/cm3
• Basalt 3.3 g/cm3
• Volatiles 1-1.5 g/cm3
• H and He ltlt0.01 g/cm3

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What have we learned?

• What does the solar system look like?
• Planets orbit Sun in the same direction and in
  nearly the same plane.
• What can we learn by comparing the planets to one
  another?
• Comparative planetology looks for patterns among
  the planets.
• Those patterns give us insight into the general
  processes that govern planets
• Studying other worlds in this way tells us about
  our own Earth

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What have we learned?

• How can we tell what planets are made of?
• The bulk density of the planets reflect the type
  of materials the planets are composed of.
• There are 4 main common types of material
• Most planets are made of a mixture of these
  materials that are not necessarily represented on
  the surface.

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What features of the solar system provide clues
to how it formed?
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• All large bodies in the solar system orbit in the
  same direction and in nearly the same plane

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Motion of Large Bodies

• Most also rotate in the direction of orbit.

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Sun

• Over 99.9 of solar systems mass
• Made mostly of H/He gas (plasma)
• Converts 4 million tons of mass into energy each
  second

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Two Main Planet Types

• Terrestrial planets (rocky worlds)
• Jovian planets
• (gas giant worlds)

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The rocky worlds are the 4 inner planets plus our
Moon
They have a solid rock surface with an iron
core and a weak or no atmosphere.
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There are 4 gas giant planets in our solar system.
These planets have NO solid surfaces just gas
and clouds that get denser as you move to their
center.
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gas giant worlds are far from the Sun
Rocky worlds are close to the Sun.
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Jupiter largest gas giant world
gas giant worlds are much larger than rocky
worlds
Earth largest rocky world
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Rocky worlds have no rings and no, or few, moons.
Gas Giant worlds have rings and many moons.
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Swarms of Smaller Bodies

• Many rocky asteroids and icy comets populate the
  solar system

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Notable Exceptions

• Several exceptions to the normal patterns need to
  be explained

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What have we learned?

• What features of the solar system provide clues
  to how it formed?
• Motions of large bodies All in same direction
  and plane
• Two main planet types Terrestrial and jovian
• Swarms of small bodies Asteroids and comets
• Notable exceptions Rotation of Uranus, Earths
  large moon, etc.