THE KUIPER BELT, OUTER SPACE (WHTM) — Pluto has a most unusual orbit. Because it’s so far from the Sun (3.7 billion miles on average), it takes the planet 248.09 years to complete one orbit.

While the larger planets in the solar system all revolve around the Sun at about the same angle (Called the ecliptic plane if you want to delve into the matter), the orbit of Pluto is tilted about 17 degrees. And while most of the planetary orbits are almost (but not quite) circular, the orbit of Pluto is more of an oval-an ellipse. (In fact, all orbits are elliptical, but some are more elliptical than others.)

Get daily news, weather, breaking news and alerts straight to your inbox! Sign up for the abc27 newsletters here

As a result of its more elliptical orbit, something interesting happens to Pluto as it makes its trip around the sun. Most of the time it will be farther from the sun than the planet Neptune, but for about 20 years, it will cross the orbit of Neptune, and be the closest to the sun of the two bodies. This happened most recently on Feb. 7, 1979-the first time since Pluto was discovered on Feb. 18, 1930.

On Feb. 11, 1999, Pluto moved back outside Neptune’s orbit, once again becoming the furthest planet in the Solar System.

On July 14, 2015, NASA’s New Horizons spacecraft sent back amazing close-up pictures of Pluto and its moon Charon, which was discovered in 1978. Pluto has five moons, Charon, Nix, Hydra, Kerberos, and Styx.

But by then, Pluto was no longer considered a planet. It was increasingly obvious the Kuiper Belt had a lot of worlds, worldlets, or maybe large iceballs. In the early 2000s, The International Astronomical Union (IAU) tackled the problem of defining what actually makes a planet a planet.

They ultimately came up with three criteria:

  • It is in orbit around the Sun.
  • It has sufficient mass to assume hydrostatic equilibrium (a nearly round shape).
  • It has “cleared the neighborhood” around its orbit.

Pluto didn’t meet that third requirement. So, when the IAU adopted the criteria on August 24, 2006, it was downgraded to a “dwarf planet”, joining Eris, Ceres, Makemake, Haumea, Gonggong, Quaoar, Sedna, and dozens, perhaps hundreds, possibly even thousands waiting to be discovered.

Pluto and its moons continue on their way, regardless of how humans try to define them. They will complete their first full orbit since their discovery on Monday, March 23, 2178. It will be closer to the Sun than Neptune again in 2227.