Once the Solar System's Ninth Planet, Pluto Was Reclassified 20 Years Ago. Here's Why Planetary Scientists and the Public Alike Love the Small Icy Body

In 1930, Clyde Tombaugh, a young observatory assistant, discovered Pluto, a small and icy body in our solar system. He was searching for a hypothetical ninth planet, "Planet X," when he noticed a moving dot in photographic images he had taken. The discovery was made at the Lowell Observatory in Arizona, where Tombaugh took up the search for the elusive planet after astronomer Percival Lowell set up the observatory in 1894. Despite Lowell's death in 1916, the discovery of Pluto became a realization of his dream.

After Tombaugh's discovery, Pluto was officially announced on March 13, 1930, during the 75th birthday celebration of Percival Lowell. The name "Pluto" was chosen because it represented the underworld in mythology, fitting the body's distant location in the solar system. Lowell Observatory continues to honor the legacy of both Lowell and Tombaugh, hosting an annual I Heart Pluto Festival and gearing up for Pluto's centennial in 2030.

In 2006, the International Astronomical Union (IAU) reclassified Pluto from a planet to a "dwarf planet." This decision was made following the discovery of Eris, another dwarf planet, which raised questions about the definition of a planet. The IAU established a set of criteria for planets, stating that a celestial body must orbit the sun, have sufficient mass to assume a round shape, and have cleared its orbit of other debris.

However, Pluto did not meet the third criterion, as its gravitational influence did not clear the Kuiper Belt of other objects.

The reclassification of Pluto sparked controversy and mixed reactions among the scientific community and the general public. Some planetary scientists, like Alan Stern, argued that the decision was a failure and that dwarf planets should be considered planets as well. Public sentiment was also divided, with many considering Pluto to be unfairly targeted. Despite the vote and the resulting controversy, the fascination with Pluto remains strong, two decades later.