Oranges. Hangers. Kuiper Belt. How Many Planets Are There?
There are eight planets circling the sun.
It is important for you to know this when you are helping your grandchildren do their homework.
Eight Planets and the Moon
They may try to correct you if you say nine, and, they will be right.
How Many Planets Do You Remember?
You may dimly remember that when you studied this subject, there were nine planets.
What happened to the ninth one, and which one is it?
It is Pluto, and it did not fall out of the sky, break up, or go find another sun to orbit around.
It is still orbiting the Earth. It even has a moon, Charon. But, the definition of planet has changed.
Pluto was only discovered in 1930, in Arizona, though astronomers had been predicting a ninth planet, Planet X, for years.
When Is a Planet Not a Planet?
How the heck can you change the definition of planet?
As it happens, astronomers discovered another body out beyond Pluto that looked a lot like a planet.
It circled the sun in the same orbit as our other planets. It was even a little bigger than Pluto.
Why Did Astronomers Change the Definition?
Astronomers decided to look again at what defines a planet. They had found a number of objects beyond Neptune in an area called the Kuiper Belt.
They might have to re-classify several of these objects as planets, instead of asteroids.
They met in 2006 and voted on a new definition of planet.
They settled on three things a planet must do:
1. Orbit the sun (just like before).
2. Have enough gravity to pull themselves into a ball (Pluto has done this).
3. Have enough gravity to clear out most of the material circling in their orbit. (Pluto has not done this).
Pluto and the newly discovered Eris were orbiting among massive ice chunks that they had not cleared out by either attracting them to their surface or slinging them out of orbit.
They were redefined as dwarf planets, along with the asteroid, Ceres.
So, the correct answer is eight – eight planets and three dwarf planets.
Did you ever make a model of the solar system in school?
What materials did you use?
How did you calculate the distance and sizes of the objects?
How long did you keep it?
To you and looking up at the stars with your grandchildren.
Carol Covin, “Granny-Guru”
Author, “Who Gets to Name Grandma? The Wisdom of Mothers and Grandmothers”
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- Dwarf planet ‘Snow White’ covered with ice (msnbc.msn.com)
- New Pluto Moon Adds Another Chapter to Dwarf Planet’s Saga (livescience.com)
Eight Planets and Our Moon
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How Many Planets Are There?
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