Given the International Astronomical Union’s (IAU) 2006 definition of a planet, which requires a celestial body to clear its orbital neighborhood, Pluto was reclassified as a dwarf planet. However, there’s ongoing debate within the scientific community and among the public about this classification. Considering the discoveries made by the New Horizons mission, the complexities of defining “clearing the orbit,” and arguments that a more geophysical definition focusing on intrinsic properties is more appropriate, is there a significant movement within the astronomical community to reclassify Pluto as a planet, and if so, what are the main arguments and proposed alternative definitions being considered, and how likely is it that the IAU’s current definition will be revised to accommodate Pluto as a planet again?

Answer

No, Pluto is not a planet again.

The International Astronomical Union (IAU), the internationally recognized authority for naming and classifying celestial bodies, established the current definition of a planet in 2006. This definition has three main criteria:

  1. It must orbit the Sun: Pluto meets this criterion.

  2. It must be massive enough for its own gravity to pull it into a nearly round shape (hydrostatic equilibrium): Pluto meets this criterion.

  3. It must have "cleared the neighborhood" around its orbit: This means that the planet must be the dominant gravitational object in its orbital zone, having either absorbed or gravitationally cleared away other objects in its vicinity. Pluto does not meet this criterion. It resides in the Kuiper Belt, a region beyond Neptune populated by numerous icy bodies, and shares its orbital space with many other objects of similar size.

Because Pluto fails to meet the third criterion, the IAU reclassified it as a "dwarf planet" in 2006. This category is for celestial bodies that meet the first two criteria but not the third. Other examples of dwarf planets include Ceres, Eris, Makemake, and Haumea.

While some scientists and members of the public still argue that Pluto should be considered a planet, the IAU’s definition remains the official standard used by astronomers worldwide. There have been no changes to the IAU definition since 2006 and no official moves to reinstate Pluto as a planet.