Final answer:
Pluto is not considered a planet by the IAU because it has not cleared its orbital neighborhood. It meets other criteria for being a planet, which has led to the term 'dwarf planet'. The reclassification has sparked debates among astronomers and the public.
Step-by-step explanation:
The International Astronomical Union (IAU) does not classify Pluto as a planet because D. It has not cleared its orbital neighborhood of other objects. When the IAU redefined the criteria for planethood in 2006, it specified three requirements. A celestial body must be in orbit around the Sun, have sufficient mass to achieve a nearly round shape (hydrostatic equilibrium), and have cleared the orbit around it. Pluto meets the first two criteria but shares its orbital zone with other icy objects and debris, leading to its classification as a dwarf planet.
There was a significant reaction to this decision among astronomers and the public, with debates and discussions about whether a dwarf planet should also count as a 'planet'. This reclassification was partly due to the discovery of trans-neptunian objects such as Eris, which is similar in size to Pluto, and others like Makemake, suggesting that Pluto was not unique in its characteristics. The presence of these additional bodies led to the understanding that Pluto needed a new category, thus becoming known as a dwarf planet.