A 10 year old girl named Kaela captured worldwide attention after writing to NASA asking for Pluto to be recognised as a planet again. NASA Administrator Jared Isaacman responded to her appeal, saying they were looking into it. The request has reignited a scientific debate that began in 2006, when Pluto was reclassified as a dwarf planet. Pluto was reclassified because it does not meet one of the International Astronomical Union’s three criteria for a planet: clearing its orbital neighbourhood of other objects. It shares its region of the Kuiper Belt with many icy bodies. However, Pluto has mountains, glaciers, a thin atmosphere and five known moons, making it a fascinating world despite its classification. The debate is not simply about whether Pluto deserves the title. Changing the definition of a planet could mean classifying many other celestial bodies, including some moons, as planets too. NASA can study Pluto and advocate for a different definition, but the International Astr...