Main Characters Astrophysicist 152 main appearances Narrator 126 main appearances Astronomer 94 main appearances Astronomer, NASA Goddard Space Flight Center 72 main appearances Planetary Scientist 27 main appearances Planetary Protection Engineer 33 main appearances Astrophysicist / Planetary Scientist, Southwest Research Institute 33 main appearances Cosmologist / Theoretical Physicist, Arizona State University 28 main appearances Planetary Scientist and Geologist 26 main appearances Theoretical Physicist, City University of New York 15 main appearances