Why is Pluto sometimes closer to the Sun than Neptune?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

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.

Pluto is sometimes closer to the Sun than Neptune because of the unique shape of its orbit. While Neptune follows a nearly circular path at a distance of approximately 30.1 astronomical units, Pluto’s orbit is highly eccentric, meaning it is significantly more elongated.1

As Pluto travels along this elliptical path, its distance from the Sun varies from 29.7 AU at its closest point (perihelion) to 49.5 AU at its farthest (aphelion). Consequently, for a small portion of its 247.69-year revolution, Pluto moves inside the orbit of Neptune.1

Despite this crossing, the two bodies will never collide. Pluto is locked in a stable 3:2 orbital resonance with Neptune, meaning it completes two orbits for every three of Neptune’s. This gravitational interaction ensures that the two objects remain separated by at least 17 AU at all times.1