Terra-3

Terra-3 refers to a fictional or theoretical extrasolar planet (exoplanet) that is Earth-like or habitable, often used in science fiction to denote a potentially habitable or already inhabited world beyond Earth and other commonly featured planets like Mars.

The term "Terra-3" implies a successor or analogue to Earth (Terra-1) and possibly Mars (often considered Terra-2 due to its potential for terraforming or having hosted past life, though this is not consistently applied). The naming convention suggests a hierarchical system based on similarity to Earth and suitability for human habitation or life in general.

The concept of Terra-3 is rooted in the search for exoplanets, particularly those within the habitable zones of their respective stars, where conditions could potentially allow for liquid water to exist on the surface. In fiction, Terra-3 often serves as a destination for human colonization, a source of alien contact, or a site of ecological or societal exploration. The specifics of a fictional Terra-3 can vary widely depending on the narrative. It may be more or less similar to Earth in terms of environment, geology, and the presence or absence of indigenous life.