Pluto’s classification as a planet has had a history of changes. Since 2006, per the International Astronomical Union’s planetary criteria, Pluto isn’t considered a planet because it hasn’t cleared the neighborhood around its orbit of other objects. However, it does meet IAU’s criteria for what constitutes a dwarf planet.

This video by CGP Grey on YouTube does a very good job of describing how Pluto’s classification has changed over time, and how Ceres and Pluto were reclassified with the discovery of numerous similar objects in their orbits.

Cover Image: Three years after NASA’s New Horizons spacecraft gave mankind our first close-up views of Pluto and its largest moon, Charon, scientists are still revealing the wonders of these incredible worlds in the outer Solar System. Marking the anniversary of New Horizons’ historic flight through the Pluto system on July 14, 2015, mission scientists released the highest-resolution color images of Pluto and Charon.

These natural-color images result from refined calibration of data gathered by New Horizons’ color Multispectral Visible Imaging Camera (MVIC). The processing creates images that would approximate the colors that the human eye would perceive, bringing them closer to “true color” than the images released near the encounter.

This image was taken as New Horizons zipped toward Pluto and its moons on July 14, 2015, from a range of 22,025 miles (35,445) kilometers. This single color MVIC scan includes no data from other New Horizons imagers or instruments added. The striking features on Pluto are clearly visible, including the bright expanse of Pluto’s icy, nitrogen-and-methane rich “heart,” Sputnik Planitia. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker

Comparison of the largest trans-Neptunian objects (TNOs): Pluto, Eris, Haumea, Makemake, Gonggong, Quaoar, Sedna, Orcus and Salacia, 2002 MS4. All except two of these TNOs (Sedna and 2002 MS4) are known to have moon(s). The top four are IAU-accepted dwarf planets while the bottom six are dwarf-planet candidates that are accepted as dwarf planets by several astronomers.

Pluto on NASA’s Solar System Exploration Site:
https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/overview/

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