1. Initial conditions:

* Formation: Planets formed from a disk of gas and dust around a young star. The distribution of this material, along with gravitational interactions, determined the initial orbital parameters of each planet.

* Planetary Migration: Early in their evolution, planets can migrate through the protoplanetary disk, changing their orbital distance and inclination.

2. Gravitational interactions:

* Sun's gravity: The Sun's gravity is the primary force that keeps planets in their orbits. However, the strength of this force varies with distance, affecting the orbital period and shape.

* Planetary interactions: Planets exert gravitational forces on each other, causing their orbits to evolve over time. This can lead to orbital resonances, where the periods of two planets are related, and perturbations, where one planet's orbit is slightly disturbed by another.

3. Other factors:

* Stellar mass: More massive stars have stronger gravitational pulls, leading to faster orbital speeds and smaller orbital radii for planets.

* Planetary mass: Planets with greater mass have stronger gravitational forces, leading to slightly more elliptical orbits.

* External influences: The gravity of other stars, passing interstellar clouds, or even the gravitational pull of a galaxy can exert subtle effects on planetary orbits over long periods.

Examples:

* Mercury and Venus: Mercury has a highly elliptical orbit due to gravitational interactions with the Sun and other planets. Venus has a nearly circular orbit, likely because of its early migration and interaction with the protoplanetary disk.

* Jupiter and Saturn: These gas giants have significantly different orbital shapes due to their early migration patterns and gravitational interactions with each other and the Sun.

In summary, the unique orbital parameters of each planet result from a complex interplay of initial conditions, gravitational interactions, and other factors that have shaped the solar system over billions of years.