Astro, Uran, Professor Ochanomizu, and Astro's classmates board a satellite called the Galileo 2, which is heading towards Saturn's moon Titan. When Astro's group arrives, they discover Dr. Tadejou, an astronomer who became disenchanted with humans and relocated to an outpost on Titan. He is accompanied by his preteen granddaughter, Yuna, who grew up on Titan listening to Tadejou's stories of the stars. The two are still waiting for their robot friend, Alfie, who left the outpost long ago to investigate a star but never returned.