A true space story
Where the Moon Came From
One young planet. One enormous crash. One new light in the sky.
-
Step 1 of 5
Earth used to be alone.
Four and a half billion years ago Earth was new, hot, and had no moon at all. The night sky was just stars.
-
Step 2 of 5
Another planet was sharing our lane.
A world about the size of Mars was circling the Sun on a path that crossed ours. Scientists call it Theia. Two objects on crossing paths eventually meet.
-
Step 3 of 5
They hit — and Earth splashed.
Not a dent — a splash big enough to leave a ring. The crash was so violent that rock turned to liquid and spray. A huge cloud of molten pieces was flung into a ring around Earth.
-
Step 4 of 5
The ring clumped into a ball.
Gravity pulled the floating pieces together. Small lumps grabbed smaller lumps, and in maybe a hundred years the ring had gathered itself into one round Moon.
-
Step 5 of 5
That is why Moon rock is Earth rock.
Same ingredients means same origin. When astronauts brought Moon rocks home, the rocks were made of nearly the same stuff as Earth's outer layers. That match is the fingerprint that gave the crash story away.
The Moon is slowly drifting away — about 3.8 cm a year, the speed your fingernails grow.
The short version
The Moon is the piece of Earth that got knocked loose and never fell back.
Try it yourself
Hold a ball of clay and smack it with another. Look at the bits that fly off — that is the Moon story in miniature.
Topics