(MUSIC)

JOAN CARTAN-HANSEN, HOST: DID

YOU KNOW IT'S POSSIBLE THAT

THE EARTH ONCE HAD TWO MOONS?

NOW, THE MOON IS ASYMMETRICAL,

THAT IS-- IT ISN'T EXACTLY

ROUND.

AND THE SURFACE OF THE FAR AND

NEAR SIDES OF THE MOON LOOK

VERY DIFFERENT.

SO, SCIENTISTS HAVE ALWAYS

WONDERED WHY.

A FEW HAVE COME UP WITH A TWO

MOON IDEA.

THE MOON WAS FORMED ABOUT FOUR

AND A HALF BILLION YEARS AGO

WHEN A MARS-SIZED OBJECT

SLAMMED INTO THE EARTH.

THE DEBRIS FROM THAT CRASH

FORMED INTO THE MOON.

SOME SCIENTISTS THINK IT IS

POSSIBLE THAT A SECOND MOON

MAY HAVE FORMED AT THE SAME

TIME.

THAT SECOND MOON EVENTUALLY

COLLIDED WITH OUR MOON AND

LEFT BEHIND THE THICK CRUST OF

THE MOON'S FAR SIDE.

NASA'S GRAIL MISSION FLEW TWO

SPACECRAFTS THAT WILL

PRECISELY MEASURED THE MOON'S

GRAVITY TO HELP SCIENTISTS

UNDERSTAND HOW THE MOON CAME

TO BE FORMED.

SO THE DATA FROM GRAIL MAY

ANSWER THE QUESTION-WAS THERE

EVER A SECOND MOON?

FOR MORE INFORMATION ABOUT THE

MOON, CHECK OUT THE SCIENCE

TREK WEBSITE.

YOU'LL FIND IT AT

IDAHOPTV.ORG/SCIENCE TREK