What characteristic of orbits is primarily due to gravitational forces?

The characteristic that highlights the influence of gravitational forces on orbits is that objects move in circular paths around the Sun. This is rooted in the principles of gravitational attraction, as described by Newton's laws of motion and universal gravitation. When an object, such as a planet or a satellite, is in orbit, the gravitational pull from a more massive body (like the Sun) works to keep it in a curved path rather than allowing it to fly off into space.

In ideal conditions, particularly when considering planetary motion, these orbits can approach circular shapes, where the gravitational pull provides the necessary centripetal force to keep the object in motion along its path. Deviations from a perfect circle can occur, leading to elliptical orbits, which are described by Kepler's laws of planetary motion; however, the underlying reason for the shape and nature of the orbit is still fundamentally linked to gravitational forces.

Other options do not correctly highlight the role of gravity in orbits. While elliptical orbits are indeed a feature of celestial mechanics, stating that orbits are always elliptical is an oversimplification. The assertion that orbits are fixed and unchanging contradicts our observations that orbits can change over time due to gravitational interactions and other forces. Lastly,