Question

What explains the spherical shape of ceres, once thought to be the largest asteroid?

Answer 1

high gravity

Ceres   Figure below   is a rocky body that orbits the Sun. It could be an asteroid or a planet. Before 2006, Ceres was thought to be the largest asteroid. Is it an asteroid? Ceres is in the asteroid belt. But it is by far the largest object in the belt. Ceres has such high gravity that it is spherical.