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How circular is Neptune’s orbit around the Sun?

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Clouds in Neptune's atmosphere — Neptune A photograph of clouds in Neptune's atmosphere, taken by Voyager 2 in August 1989. The view is from below the planet's equator, and north is up. The Great Dark Spot (center left) is 13,000 km (8,100 miles)—about the diameter of Earth—in its longer dimension. Accompanying it are bright, wispy clouds thought to comprise methane ice crystals. At higher southern latitudes lies a smaller, eye-shaped dark spot with a light core (bottom left). Just above that spot is a bright cloud dubbed Scooter. Each of these cloud features was seen to travel eastward but at a different rate, the Great Dark Spot moving the slowest.

Neptune’s orbit around the Sun is almost perfectly circular. Its orbital eccentricity—a measure of how much an orbit deviates from a perfect circle—is 0.0086. This is the second lowest eccentricity among the planets in the solar system, with only Venus having a more circular orbit.12

Because of this high degree of circularity, Neptune’s distance from the Sun varies relatively little throughout its approximately 164-year orbital period.21