Today in history On August 24, 2006 – The International Astronomical Union (IAU) redefines the term "planet" such that Pluto is now considered a dwarf planet.

In 2006, the International Astronomical Union (IAU) made one of the most controversial decisions in modern astronomy by redefining what qualifies as a planet. Prior to this, Pluto had held its place as the ninth planet of the Solar System since its discovery in 1930 by Clyde Tombaugh. However, as astronomers discovered other large objects beyond Neptune, such as Eris, which is nearly the same size as Pluto, the need for a clearer definition became urgent. The IAU established three criteria for an object to be classified as a planet: it must orbit the Sun, be massive enough for its gravity to make it nearly round in shape, and most importantly, it must have cleared its orbital path of other debris. While Pluto met the first two requirements, it failed the third because its orbit overlaps with objects in the Kuiper Belt, a region filled with icy bodies and remnants from the early Solar System.

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As a result, Pluto was reclassified as a "dwarf planet," a new category introduced by the IAU. This decision sparked widespread debate and disappointment, both within the scientific community and among the general public who had long cherished Pluto as the Solar System’s ninth planet. Many scientists felt the definition was too restrictive and excluded other celestial bodies that might deserve planetary status. Meanwhile, the public backlash was fueled by emotional attachment, with Pluto featuring prominently in textbooks, pop culture, and even childhood memories. Despite its change in status, Pluto remains an object of great interest, especially after NASA’s New Horizons mission in 2015 revealed stunning details of its surface, showing that it is far more complex and geologically active than previously imagined. This debate over Pluto’s classification continues to shape conversations about how humanity defines celestial bodies and our place in the cosmos.

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