Why do planets travel in elliptical orbits?

All planets move in elliptical orbits, with the sun at one focus. This is one of Kepler's laws. The elliptical shape of the orbit is a result of the inverse square force of gravity. The eccentricity of the ellipse is greatly exaggerated here.

Explanation:

The shape of planetary orbits follows from the observed fact that the force of gravity between two objects depends on the square of the distance between them ... Ellipses are closed so the planets we see in elliptical orbits stick around.