Triton, Neptune's largest moon, breaks the rules of the solar system. It is the only large moon that orbits backward against its planet's rotation, and it is slightly bigger than Pluto. This episode synthesizes planetary science papers, survey data and Voyager 2 mission logs to explain how Triton was likely hijacked from the Kuiper Belt as half of a binary pair, how its capture wrecked Neptune's original moons, and why it now makes up over 99.5 percent of the mass orbiting Neptune.

From there the conversation moves to Triton's alien geology: water-ice bedrock, ammonia-water cryolava, the 100-kilometer Leviathan Patera, cantaloupe terrain shaped by diapirism, and nitrogen geysers driven by a solid greenhouse effect at 38 Kelvin. The hosts cover Triton's thin nitrogen atmosphere, tholin haze, the fact that Voyager 2 mapped only about 40 perce ...