This week's guest is NASA Dawn project scientist Julie Castillo-Rogez who led the hugely successful robotic mission on the first in-depth look at the asteroid Vesta and the dwarf planet Ceres.  Castillo talks about why there's a growing consensus that Ceres may have long had habitable subsurface conditions and why we need a sample return mission to launch in 2033.  We also discuss Mars' moons of Deimos and Phobos and the first interstellar asteroid, Oumuamua.