Ceres has lived through a cosmic identity crisis: discovered and hailed as a planet in 1801, demoted to an asteroid decades later, then promoted to dwarf planet in 2006. This episode explores the king of the asteroid belt, from the Titius-Bode gap that sent the Celestial Police hunting for a missing planet, to the priest Giuseppe Piazzi who found it by accident, to the 24-year-old Carl Friedrich Gauss who invented new mathematics to recover it after it vanished behind the Sun.

We explain the two IAU tests of hydrostatic equilibrium and clearing the neighborhood, why Ceres passes one and fails the other despite holding about 40 percent of the belt's mass, and how NASA's Dawn spacecraft used ion thrusters to orbit Vesta and then Ceres in 2015. We then dig into what Dawn found: a density of 2.16 grams per cubic centimeter implying roughly a qu ...