Simplify the following text for a Grade 4 native English-speaking person.
Original: Pluto is more than twice the diameter and a dozen times the mass of the dwarf planet Ceres , the largest object in the asteroid belt . However , it is less massive than the dwarf planet Eris , a trans-Neptunian object discovered in 2005 .
Simplified: It became a `` dwarf planet '' along with Eris and Ceres .