Transcript I Might Be a Planet If-- - University of Mississippi

It Might Be a Planet If . . .
Steve Case
North Mississippi NSF GK-8
November 2006
What is a planet?
• Until recently, there was no exact definition.
• There were historically five planets.
• Uranus, Neptune, and Pluto were discovered
after the invention of the telescope.
Our Nine-Planet Solar System
Mercury
• Closest planet to the Sun
• Very hot and rocky
Venus
• About the same
size as Earth
• Covered with thick
clouds
• Farther from the
Sun than Mercury,
but hotter because
of clouds
Earth
• Our home planet
• Contains water
necessary for life
• Surrounded by a
protective
atmosphere
Mars
• Smaller than Earth
• May have once had
surface water
• Planned destination
for human
exploration
Jupiter
• Largest planet in the
Solar System
• Storms appearing as
streaks and bands
• One large storm
bigger than Earth:
Great Red Spot
• First of the “Gas
Giants”
Saturn
• Known for beautiful
rings of rock and
ice debris
• Least dense planet
(would float in
water)
• Farthest planet
known to ancient
astronomers
Uranus
• Orbits on its “side”
• Blue color comes
from methane in
atmosphere
Neptune
• Most distant of the
“Gas Giants”
• Very similar to
Uranus in size and
composition
• Great Dark Spot
similar to Jupiter’s
Red Spot
Pluto
• Until recently,
considered farthest
planet from the Sun
• Smaller than any
other planet
• Too distant to see
surface features
What About A 10th planet?
• In 2005, Eris discovered
• Larger and farther from
the Sun than Pluto
• Publicized at first as 10th
planet
• More and more objects
discovered beyond Pluto
A New Definition Needed
• If there were many
objects about the same
size as Pluto located near
Pluto’s orbit, should they
all be considered planets?
• If Pluto was a planet, why
weren’t these new objects
planets as well?
So what is a
planet?
• In 2006 the International Astronomical Union
came up with three rules for determining
whether or not a body is a planet:
– Must orbit the Sun
– Must have spherical (ball-like) shape
– Must clear orbit of other debris
1. Planets orbit their stars.
• All planets in the Solar System orbit the Sun.
• If a body in the Solar System orbits around
something other than the Sun, it is not a
planet.
2. Planets are shaped like a ball
(spherical).
• Planets have enough gravity that they were
pulled into a spherical shape when they
formed.
• If the body does not have a generally
spherical shape, it is not considered a planet.
3. Planets “sweep up” their area
around the Sun.
• Planets have enough gravity to clear their
orbits of smaller debris.
• This debris is either captured by the planet
and becomes that planet’s moon or else it is
pushed out of the planet’s orbit.
What about Pluto?
• Pluto is roughly spherically shaped, and it does orbit the Sun.
• Pluto has not cleared its orbit of other debris.
• Scientists have found many other Pluto-like objects near Pluto’s
orbit.
• Pluto was given a new classification as a dwarf planet.
Introducing the Dwarf
Planets
• Dwarf planets only fulfill two of the three
requirements to be a planet:
– They orbit the Sun.
– They are roughly spherically shaped.
– They have NOT cleared their area of all
other debris.
Our Eight-Planet Solar
System
•
•
Scientists now say that
our Solar System has only
eight planets. Pluto is no
longer considered a
planet.
Our Solar System now has
three dwarf planets:
Pluto, Eris, and Ceres.
Pluto and Eris are located
beyond Neptune. Ceres is
the largest body in the
asteroid belt between
Mars and Jupiter.
Other Members of the Solar
Family
• Besides planets and dwarf planets, there are
many other objects in the Solar System.
• Some of the major non-planet objects
include moons, asteroids, and comets.
Moons
• Bodies that orbit other things in the Solar
System besides the Sun.
• Many of the planets have moons. Earth has one
moon. Mars has two. Jupiter has over fifty.
• Even some smaller objects like dwarf planets and
asteroids have moons.
Asteroids
• Large pieces of rocky debris that orbit the Sun.
• Many are found in the Asteroid Belt between
Mars and Jupiter.
• Thought to be debris from a planet that never
formed.
Comets
• Large pieces of rock and ice that orbit the Sun
beyond Neptune.
• Occasionally are “bumped” out of orbit and fall in
toward the Sun.
• As they approach the Sun, ice and dust is burned
off to form a tail stretching away from the Sun.
Our Solar System:
• Eight planets
• Three dwarf planets
• Moons
• Asteroids
• Comets