Mercury is the closest planet to the sun, and on average, it is 57 million kilometers (35 million miles) away. That's less than 40 percent of the distance from Earth to the sun. Mercury's orbit is elliptical, though, and its distance from the sun varies by 24 million kilometers (15 million miles).
Unlike Earth, which circles the sun in a nearly circular orbit, Mercury orbits in an ellipse. The eccentricity of Mercury's orbit, which is a measure of how much it differs from a circular orbit, is 0.2056. That's more than 10 times greater than the eccentricity of Earth's orbit, which is 0.0167. In fact, it's the most eccentric orbit of any of the eight planets in the solar system.
Nearest and Farthest Distances
Unlike a circle, an ellipse doesn't have a center; instead, it has two foci, and in the case of Mercury's orbit, the sun occupies one of them. When Mercury is closest to the sun, it is only 46 million kilometers (29 million miles) distant, but when the planet is rounding the opposite focus of its orbit, it is 70 million kilometers (43 million miles) away from the sun. Because Mercury's poles aren't tilted relative to its orbit, temperature differences caused by its changing distance to the sun are the closest the planet has to experiencing seasons.
About the Author
Chris Deziel holds a Bachelor's degree in physics and a Master's degree in Humanities, He has taught science, math and English at the university level, both in his native Canada and in Japan. He began writing online in 2010, offering information in scientific, cultural and practical topics. His writing covers science, math and home improvement and design, as well as religion and the oriental healing arts.