Transcript Section 17.3

Astronomy
Chapter Eighteen: Earth Moon
and Sun
• 17.1 About the Solar System
• 17.2 The Planets
• 17.3 Other Solar System Objects
17.3 Other solar
system objects
• Pluto is a dwarf planet.
• Most of the time Pluto
is the farthest from the
sun.
• Discovered in 1930,
Pluto was named for
the Roman god of the
underworld.
17.3 Other solar system objects
• Outside the orbit of
Pluto is a region called
the Kuiper Belt.
• The Kuiper Belt
stretches to 1,000 AU
and is believed to
contain many
asteroid-size and a
few Pluto-size objects.
17.3 Pluto and the Kuiper Belt
• To avoid confusion,
astronomers no longer
count Pluto as a
planet.
• Instead, Pluto is
grouped along with
Sedna, Xena, and
similar distant bodies
in the Kuiper Belt
Objects (or KBOs).
Triton is Neptune’s largest
moon. Some astronomers
believe that Pluto may be an
“escaped” moon of Neptune.
17.3 Asteroids and comets
• An asteroid is an
object that orbits the
sun but is too small to
be considered a
planet.
• The largest asteroid,
named Ceres, is 933
kilometers (580 miles)
across.
17.3 Asteroids and comets
• We believe comets
are made mostly of
ice and dust.
• Comets revolve
around the Sun in
highly elliptical orbits.
17.3 Asteroids and comets
• The inner core of the
comet is the nucleus.
• As a comet gets
closer to the Sun, it
forms a tail.
17.3 Meteors and meteorites
• Occasionally, chunks of
rock or dust break off
from a comet or asteroid
and form a meteor.
• As Earth orbits the sun,
it passes through this
debris, creating a
meteor shower as the
small bits of dust burn
up in the atmosphere.
17.3 Meteors and meteorites
• If a meteor is large
enough to survive the
passage through
Earth’s atmosphere
and strike the ground,
it becomes a
meteorite.
Astronomy Connection
Good-bye Pluto
• On August 24, 2006,
Pluto was dropped as the
ninth planet in the solar
system.
• Astronomers had to vote
on the definition of the
term planet.
Activity
Extraterrestrial Design
• The plants and animals that live on Earth are
uniquely suited to Earth’s environment.
• In this activity, you will create an organism that
could live on another planet.