Circe is a modestly sized hydrogen-helium gas giant with traces of sulphur and chlorine. These give it its striking yellow-green tint. As the development of the Proteus colony continues, Circe will likely be developed for helium-3 mining.
- Survey: UNC: Valuable Minerals: Gas Deposit ×1 (Helium-3)
Circe is too small to be a "hydrogen-helium gas giant" (William Hubbard, The New Solar System 4th ed, 1999; p. 194). It is more likely a dense "ice giant" like Neptune or Gliese 436 b.
- In Greek mythology, Circe is a goddess, perhaps best known for her role in Homer's Odyssey, in which she transformed Odysseus' men into pigs.