While planets' orbits are often depicted as perfect circles, they're actually elliptical in shape. This means they're slightly oval-shaped rather than perfectly round.

Here's why:

* Kepler's Laws of Planetary Motion: Johannes Kepler, a 17th-century astronomer, discovered that planets orbit the Sun in ellipses, not circles.

* Gravity's Influence: The elliptical shape arises due to the gravitational pull between the planet and the Sun. A perfectly circular orbit would require a constant speed, but the planet's speed varies as it moves closer and further from the Sun.

How elliptical are planetary orbits?

Most planetary orbits in our solar system are fairly close to circular. Earth's orbit, for example, has an eccentricity (a measure of how much an ellipse deviates from a circle) of only 0.0167. This means it's very slightly elliptical. However, some planets have more elliptical orbits, such as Mercury (eccentricity of 0.206).

Conclusion:

While planets' orbits aren't perfectly circular, they're generally close enough to circular that the difference is often insignificant for many purposes.