Download I Might Be a Planet If--

It Might Be a Planet If . . .
What is a planet?
• Until recently, there was no exact definition.
• There were historically six planets.
• Uranus, Neptune, and Pluto were discovered
after the invention of the telescope.
Pluto
• Until recently,
considered the
farthest planet
from the Sun
• Smaller than any
other planet
• Too distant to see
surface features
Photo taken by New Horizons
Spacecraft 2015
What About A 10th planet?
• In 2005, Eris discovered
• Larger and farther from
the Sun than Pluto
• Publicized at first as the
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?
What has been one source of
confusion surrounding
planets in our solar system?
Because ….. has been unclear, this has
made …… somewhat confusing.
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. (Kuiper Belt)
• Scientists have found many other Pluto-like objects near Pluto’s
orbit.
• Pluto was given a new classification as a dwarf planet.
What characteristics define a
planet?
To be a planet, it must ….
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
FIVE dwarf planets: Pluto,
Eris, and Ceres, Haumea,
and Makemake. Pluto,
Eris, Haumea, and
Makemake are located
beyond Neptune- in the
Kuiper Belt. 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 SIXTY.
• 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.
CometsOort Cloud
• 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:
• THE SUN!!!!!!
• Eight planets
• Five dwarf planets
• Moons
• Asteroids
Is there a possible 9th planet?
Does it...
Mars
Pluto
Europa (one
of Jupiter’s
moons)
Comets
Asteroids
Orbit its
star?
Have a
spherical
shape?
Have enough mass (and
thus, gravity) to clear its
surroundings of smaller
debris?