Once known as the ninth planet in our solar system, Pluto was reclassified as a dwarf planet in 2006. The change came after the International Astronomical Union voted on August 24, 2006, to redefine what counts as a planet. This decision followed the discovery of Eris, a celestial body similar in size to Pluto but with more mass. Eris and other newly found objects prompted scientists to reconsider how they define planets. The IAU introduced a new definition that required a celestial body to orbit the sun, be large enough to form a sphere, and clear its orbital path of other objects. Pluto did not meet the third requirement because it shares its orbital neighborhood with many Kuiper Belt objects.
Clyde Tombaugh, an observatory assistant from Illinois, discovered Pluto in 1930, according to Smithsonian Magazine. He built his own telescopes and was working at the Lowell Observatory when he spotted the moving dot on photographic plates. The discovery happened while he was using a blink comparator to compare images taken days apart. That tiny moving dot turned out to be the icy world now known as Pluto. The announcement of Pluto’s discovery came on March 13, 1930, coinciding with the 75th birthday of Percival Lowell. Lowell had searched for a ninth planet beyond Neptune but died before seeing the discovery made at his own observatory.
Pluto has five moons named Charon, Nix, Hydra, Kerberos, and Styx. Charon is about half the size of Pluto, making it the largest moon relative to its planet in the solar system. The Lowell Observatory still celebrates Pluto’s discovery with an annual festival every February. Flagstaff, Arizona, has embraced its connection to Pluto and calls itself Plutotown, USA.
Even after losing planetary status, Pluto continues to draw public interest and scientific curiosity. The reclassification of Pluto led to a broader understanding of the solar system’s diversity, according to a report from Space.com. It highlighted how many objects in the outer solar system are not planets but rather dwarf planets. Pluto’s discovery and reclassification helped scientists realize that there are many icy bodies beyond Neptune. These discoveries prompted a need to clarify what makes an object a planet versus a dwarf planet. Pluto’s orbit crosses paths with other objects in the Kuiper Belt, which is why it was not considered to have cleared its neighborhood. Some people still argue for Pluto’s return to planetary status, but scientists say that would open the door to many other dwarf planets.
The debate over Pluto’s classification shows how science evolves as new tools and discoveries come into play, CNET reported. New telescopes and space missions have revealed more objects in the outer solar system that are similar to Pluto. These findings have made it clear that Pluto is part of a larger group of icy bodies in the Kuiper Belt. The definition of a planet now includes three criteria: orbiting the sun, being large enough to be spherical, and clearing its orbital path. Pluto meets the first two criteria but fails to clear its orbit, placing it in the dwarf planet category.
The International Astronomical Union also recognizes five other dwarf planets: Pluto, Ceres, Eris, Makemake, and Haumea. Some scientists believe that Pluto’s reclassification was necessary to better categorize celestial objects in our solar system. The debate continues, but some scientists accept that Pluto is not a planet anymore. Still, many people feel nostalgic about Pluto’s former status as a planet. Some argue that Pluto should be reinstated, but the scientific consensus holds that it fits better in the dwarf planet category.
Pluto’s legacy lives on not just as a celestial body, but as a symbol of how science continues to evolve.
IMAGE: A photomap of Dithering image based on pictures of Pluto from 2002 to 2003 taken by the Advance Camera for Survey of the Hubble telescope.. Photo: NASA, ESA, and M. Buie (Southwest Research Institute) / Wikimedia, Public domain