Download Foundation 1 - Discovering Astronomy

Chapter 11:
Pluto and
Dwarf
Planets
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.
The discovery of Charon
HST discovers new moons!
2005
2011
2012
What is Pluto?
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)?
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 !
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 !
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?