When I consider your heavens,
the work of your fingers,
the moon and the stars,
which you have set in place, what is man that you are mindful of him,
the son of man that you care for him? Psalm 8:3-4

There has been some interesting scientific evidence regarding the need and existence of other planets.   Here are a few reasons why God created other planets:

1. The planets which orbit around the sun, act as a barrier, drawing meteors into their gravitational pull and keeping the earth safe.
2. They also display the power of God to create other planets with the blink of an eye.
3. They show the variety and creativity of the Lord.
4. They helped those in earlier times with direction.
5. They give us perspective on our size in this universe.
6. Because God can.