Facts About the Rate of the Revolutions of Planets Around the Sun

Shortest Orbit Period

• Mercury completes its orbit around the sun in about 88 Earth days, faster than any other planet in the solar system. As the closest planet to the sun, it has the shortest orbit circumference at about 224 million miles and travels faster on that short circuit than any other planet, at an average velocity of about 106,000 mph.

Elliptical Orbits

• Planets revolve around the sun in ellipses rather than circles, with the sun at one foci. The planets travel faster as they approach the sun and slower as they recede from the sun. The point at which a planet is closest to the sun is termed perihelion, while the point at which it is farthest from the sun is called aphelion.

Orbit Eccentricity

• The amount a planet's orbit deviates from a perfect circle is called orbit eccentricity. Most of the planets have very small eccentricities meaning they have nearly circular orbits. Mercury gained the distinction as having the most elliptical orbit after the previous title holder, Pluto, was reclassified as a dwarf planet.

Orbit Inclination

• Imagine a disc extending from the sun on which the Earth orbits. This plane is called the ecliptic. It may be simpler to conceptualize all the planets orbiting the sun on the ecliptic, but the other planets actually orbit slightly above or below this plane. Most of the planets do orbit within a few degrees of this plane, but Mercury has a 7-degree inclination and Pluto has a 17-degree inclination.

Longest Orbit Period

• The longest orbit period of the planets is Neptune, which is also the slowest planet in its orbit. It takes over 164 Earth years for Neptune to complete its more than 17-billion-mile journey around the sun. Prior to reclassification as a dwarf planet, Pluto had the longest, slowest orbit traveling 22 billion miles in just under 248 years.

Crossing Orbits

• Even before Pluto changed status from planet to dwarf planet, it periodically lost the distinction as furthest from the sun. From 1979 to 1999, Pluto's orbit took it closer to the sun than Neptune. Despite this apparent crossing of paths, Neptune and Pluto are in no danger of colliding since Pluto's orbit is greatly inclined from the ecliptic and the two bodies are in resonance so that Pluto orbits twice for every three times Neptune orbits. In fact, Neptune and Pluto only come within 17 A.U of each other -- one A.U., or astronomical unit, is the average distance between the Earth and the sun, about 93 million miles.