How does gravity maintain the shape of the solar system?

Gravity maintain the shape of the solar system by pulling in the sun and the planets to stay together in the orbits.
Without the Gravity , The planets could either 
1. Stray apart from each other, which may kill all the organism on earth (we need to maintain a specific distance toward the sun as our primary source of energy)
2 . Colliding and destroying each other

Independent variable is something that is changed in a experiment.