Double Planet

Double Planet is an informal term used to describe two planets very close to each other.

The formal term for two planets very close to each other is:

                                      "binary system"

     (Pluto and Charon Pluto's moon are considered to be double dwarf planet systems.)

You're probably thinking...if Pluto and it's moon are double planets, then why isnt our Earth and our moon a double planet?

well, the cutoff point for deciding between a planet-satellite or double-planet system is based on the location of the center of mass of the two objects (barycenter). If the barycenter is not located under the surface of either body, then one usually refers to the system as a double-planet system. and since the barycenter of the earth-moon system lies underneath the surface of the earth, these two bodies are informally referred to as a planet-satellite system. 

HERE IS A WAY TO REMEMBER DOUBLE PLANET!

To help remember DOUBLE PLANET just think of double means 2 so Double Planet sounds like 2 planets. Think of it as 2 planets close to each other!  

DID THAT HELP??

Quiz time

   1) Earth and its moon is considered to be a what?

     a) double planet                 b) friendly neighbor

     c) planet-sattelite system   d) your cousin twice removed

     2) What is the name of pluto's moon?

     a) lucy                                  b) karen

     c) charon                              d) polaris

     3) if "double planet" is an informal term, what is the formal term for two planets very close to each other?

      a) triple planet                       b) planetary system

      c) best friend                         d) binary system

                        Answers are at the bottom of the Wiki page 

                          We need to know about double planets for many reasons.

If you were a scientist studying space, you would want everything to be organized so that it would be easier to determine what things are and discover more. well, if you come across a planet, say Pluto and Charon and want to know what to categorize them as, you would need to know what a double planet is and what sets them apart from other planets that are near each other, like the earth and our moon. that is why we need to know what a double planet is and why we study it.

 Answers to quiz:

1) C

2) C

3) D

I hope you got them all correct!

"Double Planet." Wikipedia. 2008. Wkipedia Foundation, Inc.. 9 May 2008 <http://en.wikipedia.org/wiki/Double_planet>.

Darling, David. "Double planet ." The Internet Encyclopedia of Science. 2008. 11 May 2008 .