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(MUSIC)

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JOAN CARTAN-HANSEN, HOST: DID

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YOU KNOW IT'S POSSIBLE THAT

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THE EARTH ONCE HAD TWO MOONS?

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NOW, THE MOON IS ASYMMETRICAL,

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THAT IS-- IT ISN'T EXACTLY

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ROUND.

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AND THE SURFACE OF THE FAR AND

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NEAR SIDES OF THE MOON LOOK

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VERY DIFFERENT.

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SO, SCIENTISTS HAVE ALWAYS

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WONDERED WHY.

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A FEW HAVE COME UP WITH A TWO

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MOON IDEA.

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THE MOON WAS FORMED ABOUT FOUR

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AND A HALF BILLION YEARS AGO

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WHEN A MARS-SIZED OBJECT

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SLAMMED INTO THE EARTH.

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THE DEBRIS FROM THAT CRASH

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FORMED INTO THE MOON.

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SOME SCIENTISTS THINK IT IS

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POSSIBLE THAT A SECOND MOON

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MAY HAVE FORMED AT THE SAME

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TIME.

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THAT SECOND MOON EVENTUALLY

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COLLIDED WITH OUR MOON AND

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LEFT BEHIND THE THICK CRUST OF

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THE MOON'S FAR SIDE.

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NASA'S GRAIL MISSION FLEW TWO

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SPACECRAFTS THAT WILL

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PRECISELY MEASURED THE MOON'S

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GRAVITY TO HELP SCIENTISTS

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UNDERSTAND HOW THE MOON CAME

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TO BE FORMED.

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SO THE DATA FROM GRAIL MAY

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ANSWER THE QUESTION-WAS THERE

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EVER A SECOND MOON?

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FOR MORE INFORMATION ABOUT THE

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MOON, CHECK OUT THE SCIENCE

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TREK WEBSITE.

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YOU'LL FIND IT AT

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IDAHOPTV.ORG/SCIENCE TREK