Sixth Grade
Worksheets
Is Pluto a Planet?
Caption: Size comparison of Earth and its moon to Pluto and Charon
It is; it isn't. It is, but with some restrictions. No, it isn't. Yes, it is, sort of. These are the arguments about poor Pluto. Is it a planet, or isn't it?
Pluto was once thought of as the smallest planet. It was also known as the coldest planet since it is the farthest from the sun. It was discovered in 1930. Since then, scientists have had trouble deciding if it really is a planet or not.
In 2006, the International Astronomical Union (IAU) made some new "planetary rules." According to the new rules, a true planet must do three things. First, it must orbit the sun. Secondly, it must be big enough for gravity to make it into a round ball. And lastly, it must have cleared out its orbital neighborhood. There can't be any "junk" floating around it.
