When it was discovered, it was believed to be larger than earth. Now, it is known to have a diameter of about twice the width of texas and half that of mercury. With the discovery of ceres, sedna, eris, haumea, makemake, gonggong, quaoar and orcus: a list that is expected to grow over time, it was decided to set a permanent number on major planets and relegate the smaller ones to a separate class.