Final answer:
The celestial object discovered in 2005 is Eris, option b). Eris is a dwarf planet, similar to Pluto, and was one of the discoveries that expanded our knowledge of the Kuiper Belt and trans-Neptunian objects.
Step-by-step explanation:
In 2005, astronomers announced the discovery of the celestial object known as Eris. Querying which celestial object was discovered in 2005 gives us the answer: b) Eris. Eris is one of the largest known dwarf planets in our solar system, similar in size to Pluto. Just as Pluto has moons and unique characteristics distinguishing it from other planets, so does Eris with its own moon. The discovery of Eris, along with other trans-Neptunian objects (TNOs) such as Makemake and Haumea, led to a reclassification of Pluto and these large objects in the outer solar system as dwarf planets.
Eris's discovery emphasized that Pluto was not the only one of its kind in the outer reaches of our solar system but rather a part of a larger group of bodies beyond Neptune's orbit, specifically within the Kuiper Belt. This belt contains many TNOs, dwarf planets, and is an area where short-period comets originate. The findings have broadened our understanding of the solar system and continued the tradition of naming celestial bodies after mythological figures, including gods from various cultures beyond Roman mythology.