Astronomy Fun Fact #54
The planet in our solar system with the most eccentric (meaning least circular) orbit is Mercury.
Eccentricity is measured on a scale from 0 (perfectly circular) to 1 (escaping the system). Earth's eccentricity is 0.017 and Mercury's is 0.205.
The picture shows how both Earth and Mercury compare to circular orbits at their positions in the solar system.