Download History of Planets

1/4/2011
Definition:
What is a Planet?
planhthV
(planetes)
How many planets are there in the
solar system?
A wanderer
How Many Planets?
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Ancient view
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Post Copernicus
6
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1781 (Herschel)
7
7
IAU 2006 Planet Definition
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A PLANET is a celestial body that :
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(2) A "dwarf planet" is a celestial body that:
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1865
83
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Early 20th century
8
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Simplified definition
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Orbits the sun
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Has enough mass to be round
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Has enough gravity to clear orbit of other
bodies
(a) is in orbit around the Sun
(b) has sufficient mass for its self-gravity to overcome rigid body forces
so that it assumes a hydrostatic equilibrium (nearly round) shape
c) has cleared the neighborhood around its orbit.
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces
so that it assumes a hydrostatic equilibrium (nearly round) shape
(c) has not cleared the neighborhood around its orbit
(d) is not a satellite.
(3) All other objects except satellites, orbiting the Sun shall be
referred to collectively as "Small Solar-System Bodies".
Forming Planetary System
Planetesimals
1
1/4/2011
The Terrestrial Planets
Planetesimals
Protoplanets
Debris
Jovian Planets
Ida with Dactyl
Itokawa
Comet McKnaught
Gaspera
Earth for comparison
Eris
Phobos
2