Erillis

Erillis is a fictional terrestrial exoplanet frequently depicted in science fiction and worldbuilding literature. In these works it orbits a sun-like star in the Delphus system, roughly 200 light-years from Earth. It is described as a rocky world with a substantial global ocean. Estimates place its radius at about 1.3 Earth radii and its mass around 2 Earth masses.

Erillis's orbit is near-circular, with an orbital period of approximately 420 days and an axial tilt of about 12 degrees, producing moderate seasons. The atmosphere is primarily nitrogen with trace oxygen, and surface pressure close to Earth's. The result is a temperate climate moderated by the oceans.

Geologically active, Erillis features subduction zones and mantle plumes that drive long-term tectonic and volcanic activity. The planet hosts a shallow continental shelf and episodic uplift, while ocean currents transport heat, supporting relatively stable coastal climates and seasonal sea-ice patterns in some eras.

Life and habitability: No confirmed life exists in the canonical material, but speculative xenobiology includes photosynthetic microbes in shallow seas and bioluminescent organisms in the deep ocean. In-universe exploration relies on orbital spectrometers, submersible probes, and autonomous rovers; Erillis serves as a test case for climate and ocean models.

Name and portrayal: The name Erillis is invented within the stories, drawing on a fictional linguistic tradition. In reference works it is presented as an archetype of ocean-world habitability and is used in discussions of planetary climates, biosignature prospects, and planetary exploration.