Isaac Newton concluded that gravity keeps the planets in orbit around the Sun. He formulated the Law of Universal Gravitation, which states that:

* Every particle in the universe attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

This means that:

* The more massive the objects, the stronger the gravitational force between them.

* The closer the objects, the stronger the gravitational force between them.

The Sun is a massive object, and its gravity pulls on the planets, keeping them in orbit. The planets have enough velocity to not fall directly into the Sun, and instead, they constantly fall *around* it, tracing an elliptical path.