Gravity does not directly keep objects in motion around the Sun. Objects that orbit the Sun, such as planets, asteroids, and Halley's comet, stay in orbit because of their initial motion and the conservation of angular momentum.

Initially, the cloud of gas and dust from which the solar system formed was rotating and collapsing. As the solar system took shape, the angular momentum of the rotating cloud was transferred to the orbiting objects. This means that the objects inherited the rotational motion of the original rotating cloud.

Gravity plays an indirect role in maintaining the orbits of objects around the Sun by providing the force that keeps them from moving in a straight line. Without gravity pulling them inward, the objects would fly off in a straight path due to their initial motion. However, the gravitational attraction of the Sun ensures that their paths continue to curve and they remain in orbit.

In essence, it's the combination of the initial rotational motion of the collapsing gas cloud, coupled with the gravitational attraction of the central mass (the Sun), that keeps objects in orbit around the Sun.