The force that pulls everything toward the Earth
gravity
Not like anyone or anything else
unique
The outside part of something
surface
All physical substances or a substance of a particular kind
matter
The central part of an object
core
A straight line across a circle through the center
diameter
A person who studies or knows a lot about the sun, moon, planets and stars
astronomer
A space craft without people that collects information and sends it back to Earth
space probe
A large hole in the ground caused by something large hitting it
crater
How far it is from one place to another
distance
The path of a planet or an object thats moving around another thing space
orbit