The planet that was farthest from the sun until 1999 was Pluto.

While Pluto is now classified as a dwarf planet, it was considered the ninth planet in our solar system until 2006. In 1999, the discovery of Eris, a trans-Neptunian object larger than Pluto, challenged Pluto's status as the outermost planet. This ultimately led to the International Astronomical Union's decision to reclassify Pluto and other similar objects as dwarf planets.