A planet is any body in orbit around the Sun that has
enough gravity to form a sphere and that has cleared
the neighborhood near its orbit of smaller objects.
The inner planets
are mostly rock and
The outer planets
are mostly gas and
The planets that are made of gas and
dust are much bigger than the planets
that are made of rock and metal.
Which of the following planets is mostly rock and metal?
Saturn is made of gas and dust. Do you think it
would be bigger or smaller than Mars?
Bigger than Mars
Smaller than Mars
Match each planet name to the diagram.
What is Neptune mostly made out of?
Metal and Rock
Dust and Gas
Astronomers are planning to define
a new type of planet.
This new type is a “plutoid” or “dwarf
Plutoids are not big enough to clear their
path of other objects.
Pluto is a plutoid. So are Ceres, Eris,
Makemake, and Haumea.
Pluto is in orbit around the sun, but it has a smaller
object in its immediate neighborhood.
Is it a planet?
Yes, but it’s a