Which planet has an elliptical orbit around the Sun, rather than a circular one?

• A. Mercury
• B. Earth
• C. Venus
• D. Mars

Answer: (A)

Orbits around the Sun are ellipses, not perfect circles. An ellipse has eccentricity that measures how stretched it is—the closer to zero, the more circular the path. Among the options, Mercury has the most elongated orbit, so its path around the Sun is noticeably elliptical rather than circular. Earth’s and Venus’s orbits are very close to circular (low eccentricities), while Mars is more elongated than Earth and Venus but still less stretched than Mercury. This combination means Mercury’s distance to the Sun and its speed vary more dramatically over its year, illustrating a clear elliptical orbit. For context, Mercury’s eccentricity is about 0.21, Earth about 0.02, Venus about 0.007, and Mars about 0.09.