General Properties of the Solar System continued

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General Properties of the Solar System (continued)
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Announcements

• Reading for next class
• Finish Chapter 8 through section 8.6 (not the
  last section)
• Homework 2 Due now
• Quiz today
• Closed book, closed note, no electronic devices
  (like it will be for the exam)
• First Exam Next Thursday (2/21)
• Brief review and discussion of the exam format on
  Tuesday
• Come prepared with questions
• Study session date/time/location will be
  announced on course website and facebook page
  (please come prepared with specific questions to
  ask the TA)

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Two basic classes of PlanetsTerrestrial and
Jovian (Gas Giants)

• Terrestrial
• Mercury, Venus, Earth, Mars
• Composed of mostly heavier elements (iron,
  silicon, etc.).
• Gas Giants
• Jupiter, Saturn, Uranus, Neptune
• Composed mostly of lighter elements such as H
  (hydrogen) and He (helium).
• Pluto is different

PTYS/ASTR 206
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Distribution of Planet Masses
PTYS/ASTR 206
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Distribution of Planet Densities

• Density Mass / Volume

PTYS/ASTR 206
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Seven large moons are almost as big as the
terrestrial planets

• Comparable in size to the planet Mercury
• The remaining satellites of the solar system are
  much smaller

PTYS/ASTR 206
Telescopes / Solar System 2/12/08
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Solar-system inventory continuedThe Sun

• Most massive object in the solar system
• Formed at about the same time as all of the
  planets, and from the same material
• The source of energy that keeps is shining for
  billions of years is thermonuclear fusion

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Solar-system inventory continued The Solar Wind

• The solar corona is in a constant state of
  expansion and continues off into space, creating
  the Solar Wind
• The Solar Wind is a plasma the 4th state of
  matter (solid, liquid, and gas are the other 3)
• Its existence was predicted based on observations
  of comet tails (the blue ion tail in the picture
  is directed along the solar wind)

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Solar-system inventory continuedSmall chunks of
rock and ice also orbit the Sun

• Asteroids are small, rocky objects, while comets
  and Kuiper-belt objects are made of dirty ice (or
  icy dirt?)
• All are remnants left over from the formation of
  the planets
• Some of them contain the primordial material from
  which the solar system is made

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• Kuiper Belt Objects
• Beyond the orbit of Neptune
• Distributed loosely along the ecliptic plane
• Pluto is a large KBO

• Asteroid belt
• Between the orbits of Mars and Jupiter
• Probable origin of Near-Earth objects

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Solar-system inventory continued The outer
reaches of the Solar System

• The Heliosphere
• The cavern carved out of the interstellar gas by
  the solar wind
• The Oort Cloud
• contains billions of comet nuclei in a spherical
  distribution that extends out to 50,000 AU from
  the Sun
• Intermediate period and long-period comets are
  thought to originate in the Oort cloud
• As yet no objects in the Oort cloud have been
  detected directly

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Planet Properties Internal Structure

• All are differentiated
• Terrestrial planets all have a metallic core
• Why not one type of material all the way through?
• Rocky mantle
• Crust of some sort?
• the proportions of the core, mantle, crust,
  differ for each of the terrestrial planets
• The interior of gas giants is usually composed of
  the same material, just in a different state
  (gas, liquid, etc.)

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Planet Properties Volcanoes

• some terrestrial planets have them,
• some dont --- why?

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Will a planet have active volcanoes?

• Requires Heat
• After the planets formed, they were very hot
• Big planets cool slower
• Small planets cool more rapidly
• Big terrestrial planets are active longer
• Fewer craters
• More likely to have active volcanoes
• Earth and Venus for example both of these
  worlds also have very few visible craters

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Planet PropertiesImpact Cratering

• When an asteroid or comet strikes the surface of
  a terrestrial planet or moon, the result is an
  impact crater
• Geologic activity renews the surface and erases
  craters, so a terrestrial world with extensive
  cratering has an old surface and little or no
  geologic activity
• Because geological activity is powered by
  internal heat, and smaller worlds lose heat less
  rapidly than larger ones
• as a loose general rule the smaller a world
  is, the more heavily cratered it will be

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Todays quiz

• Be sure to fill in the ovals for your name (last
  name first!!!)
• Be sure to write the letter of your quiz (A, B,
  or C) on the top of the scantron sheet
• Closed book, closed notes, no electronic devices
• The quiz has 15 questions (front and back)
• Fill in the oval corresponding to your answer on
  the scantron sheet using a 2 pencil
• Only turn in the scantron sheet you may take
  the quiz itself with you when you leave
• You may leave when you are finished but please
  do so as quietly as possible and leave through
  the North Entrance (upper right door)