Here's why:

* Gravity: The sun's gravity pulls on the planet, keeping it from flying off into space.

* Motion: The planet is also moving, carrying momentum.

* Balance: The combination of the sun's gravity and the planet's motion results in a curved path. This path is not a perfect circle, but a slightly elongated shape called an ellipse.

Key Features of an Elliptical Orbit:

* Focus: The sun is located at one focus of the ellipse.

* Eccentricity: The shape of the ellipse is determined by its eccentricity. A perfectly circular orbit has an eccentricity of 0, while a more elongated ellipse has a higher eccentricity.

* Perihelion and Aphelion: The point in the orbit where the planet is closest to the sun is called perihelion. The point where it's farthest from the sun is called aphelion.

It's important to note that orbits aren't always perfectly elliptical. Other planets and celestial bodies can exert small gravitational influences, causing slight variations in the planet's path.