The discovery of Eris marked a significant milestone in planetary science, occurring at Palomar Observatory by a team led by astronomer Mike Brown. Eris is located in the Kuiper Belt, a region of the solar system beyond the orbit of Neptune filled with icy bodies. Initially designated as 2003 UB313, it was identified as the most massive known dwarf planet, surpassing Pluto in size. This finding not only expanded our understanding of the solar system's composition but also raised important questions about the classification of celestial bodies. The observational efforts involved sophisticated technology, including advanced telescopes and imaging techniques, enabling astronomers to detect this distant object. Eris has a diameter of approximately 2,326 kilometers and is composed primarily of ice and rock, highlighting diverse geological characteristics.

The discovery created substantial discourse among astronomers and the larger scientific community, leading to the convening of the International Astronomical Union (IAU) in 2006. They ultimately defined the term 'planet,' resulting in Pluto's reclassification as a 'dwarf planet.' The introduction of criteria for planet classification illustrates how Eris played a crucial role in redefining our understanding of planetary bodies and their categorization.