Foundation 1 - Discovering Astronomy

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Chapter 11 Pluto and Dwarf Planets
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Pluto Ruler of the Underworld
Pluto was discovered by Clyde Tombaugh in 1930 by
comparing one image of the sky taken one night
with an image taken 6 nights later.
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The discovery of Charon
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HST discovers new moons!
2005
2011
2012
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What is Pluto?
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What is Pluto?

• Strange planet located far out from the Sun with
  gas giants but small size and very elliptical and
  highly inclined orbit
• Pluto is a mixture of ices and rocks
• composition similar to satellites of giant
  planets than terrestrial planets
• Could be captured Kuiper Belt Object (e.g.
  comet)?

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IAU Definition
A "planet" is a celestial body that (a) is in
orbit around the Sun, (b) has a nearly round
shape (c) and has cleared the neighborhood
around its orbit.
8 Planets !
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A dwarf planet is a celestial body that (a)
is in orbit around the Sun, (b) has a nearly
round shape (c) and is neither a star, a planet,
or a moon
40 Dwarf Planets !
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Should Pluto be a Planet?

• Write down the three characteristics of a planet.
• Why is Pluto not a planet anymore?
• What type of object is it?
• In your opinion, should we keep Pluto as a
  planet? Why or why not?