Chapter 7 Our Planetary System

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Chapter 7Our Planetary System
Earth, as viewed by the Voyager spacecraft
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What does the solar system look like?
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• Eight major planets with nearly circular orbits
• Pluto is smaller than the major planets and has a
  more elliptical orbit

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• Planets all orbit in same direction and nearly in
  same plane

http//observe.phy.sfasu.edu/courses/ast105/lectur
es105/chapter06/orbit_and_rotation_planets.htm
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Thought QuestionHow does the Earth-Sun distance
compare with the Suns radius

• Its about 10 times larger.
• Its about 50 times larger.
• Its about 200 times larger.
• Its about 1000 times larger.

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Thought QuestionHow does the Earth-Sun distance
compare with the Suns radius

• Its about 10 times larger.
• Its about 50 times larger.
• Its about 200 times larger.
• Its about 1000 times larger.

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Bodes Law

• a simple rule that gives the distances of the
  planets from the Sun

where N0, 3, 6, 12, 24for Mercury, Venus,
Earth, Mars, etc.
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Planet N Bodes Law Radii
True Orbital Radii
Mercury 0 (04)/10 0.4 AU 0.39 AU
Venus 3 (34)/10 0.7 AU 0.72 AU
Earth 6 (64)/10 1.0 AU 1.00 AU
Mars 12 (124)/10 1.6 AU 1.52 AU
____ 24 (244)/10 2.8 AU _______
Ceres 24 2.88 AU
Jupiter 48 (484)/10 5.2 AU 5.2 AU
Saturn 96 (964)/10 10.0 AU 9.5 AU
Uranus 192 (1924)/10 19.6 AU 19.2 AU
Neptune ? ? 30.1 AU
Pluto 384 (3844)/10 38.8 AU 39.5 AU
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What does Bodes Law tell us?

• Bode's Law predicted that there should be a
  planet between the orbits of Mars and Jupiter.
• The "missing planet" turned out to be the
  asteroid belt.

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What are the major features of the Sun and
planets?
Sun and planets to scale
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What to know

• Main features
• Rock or Gas?
• Color?
• Rings?
• Clouds?
• Moons? Names of major moons
• Anything else that is odd or intersting.

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Planets are very tiny compared to distances
between them.
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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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Mercury

• Made of metal and rock large iron core
• Desolate, cratered long, tall, steep cliffs
• Very hot and very cold 425C (day), 170C
  (night)
• No atmosphere
• Only slightly larger than Earths Moon.

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Venus

• Nearly identical in size to Earth surface
  hidden by clouds
• Hellish conditions due to an extreme greenhouse
  effect
• Even hotter than Mercury 470C, day and night

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Earth
Earth and Moon to scale

• An oasis of life
• The only surface liquid water in the solar
  system
• A surprisingly large moon

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• The Moon
• Many craters
• Maria

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Mars

• Looks almost Earth-like, knee high atmosphere
• Giant volcanoes (Olympus Mons), a huge canyon
  (Valles Marineris), and polar caps (CO2).
• Water flowed in the distant past could there
  have been life?

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Moons of Mars

• Two small moons
• Phobos Greek for fear
• Deimos- Greek for dread or panic

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Jupiter

• Much farther from Sun than inner planets
• Mostly H/He no solid surface
• 300 times more massive than Earth
• Great Red Spot
• Many moons (60), rings

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Jupiters moons can be as interesting as planets
themselves, especially Jupiters four Galilean
moons

• Io (shown here) Active volcanoes all over
• Europa Possible subsurface ocean
• Ganymede Largest moon in solar system
• Callisto A large, cratered ice ball

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• Jupiter has a thin ice ring.

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Saturn

• Giant and gaseous like Jupiter
• Spectacular rings Cassinis Division
• Many moons, including cloudy Titan
• Cassini spacecraft currently studying it

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Rings are NOT solid they are made of countless
small chunks of ice and rock, each orbiting like
a tiny moon.
Artists conception
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Cassini probe arrived July 2004 (Launched in
1997)
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Uranus

• Smaller than Jupiter/Saturn much larger than
  Earth
• Made of H/He gas hydrogen compounds (H2O, NH3,
  CH4)
• Extreme axis tilt
• Moons rings

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Neptune

• Similar to Uranus (except for axis tilt)
• Great Dark Spot
• Many moons (including Triton)

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Pluto (Not a Planet and not Red)

• Much smaller than any of the planets
• Icy, comet-like composition
• Its moon Charon is similar in size

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Thought QuestionWhat process created the
elements from which the terrestrial planets were
made?

• The Big Bang
• Nuclear fusion in stars
• Chemical processes in interstellar clouds
• Their origin is unknown

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Thought QuestionWhat process created the
elements from which the terrestrial planets were
made?

• The Big Bang
• Nuclear fusion in stars
• Chemical processes in interstellar clouds
• Their origin is unknown

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What have we learned?

• What are the major features of the Sun and
  planets?
• Sun Over 99.9 of the mass
• Mercury A hot rock
• Venus Same size as Earth but much hotter
• Earth Only planet with liquid water on surface
• Mars Could have had liquid water in past
• Jupiter A gaseous giant with the great red spot
• Saturn Gaseous with spectacular rings
• Uranus A gas giant with a highly tilted axis
• Neptune Gas giant with great dark spot
• Pluto An icy misfit more like a comet than a
  planet

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What features of the solar system provide clues
to how it formed?
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Motion of Large Bodies

• All large bodies in the solar system orbit in the
  same direction and in nearly the same plane
• Most also rotate in that direction

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Two Main Planet Types

• Terrestrial planets are rocky, relatively small,
  and close to the Sun
• Jovian planets are gaseous, larger, and farther
  from Sun

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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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Special Topic How did we learn the scale of the
solar system?
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Transit of Venus

• Apparent position of Venus on Sun during transit
  depends on distances in solar system and your
  position on Earth

Transit of Venus June 8, 2004
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Measuring Distance to Venus

• Measure apparent position of Venus on Sun from
  two locations on Earth
• Use trigonometry to determine Venus distance
  from the distance between the two locations on
  Earth

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How do robotic spacecraft work?
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Flybys

• A flyby mission flies by a planet just once
• Cheaper than other mission but have less time to
  gather data

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Orbiters

• Go into orbit around another world
• More time to gather data but cannot obtain
  detailed information about worlds surface

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Probes or Landers

• Land on surface of another world
• Explore surface in detail

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Sample Return Missions

• Land on surface of another world
• Gather samples
• Spacecraft designed to blast off other world and
  return to Earth
• Apollo missions to Moon are only sample return
  missions to date

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Combination Spacecraft

• Cassini/Huygens mission contains both an orbiter
  (Cassini) and a lander (Huygens)