Epona alien planet, artwork. This designed alien planet is called Epona. It was modelled in the 1990s by a worldbuilding group who designed it according to scientific principles. As well as Epona, an entire planetary system was modelled around the parent star Taranis (82 Eridani), 21 light years from Earth. Epona has an equatorial diameter of 10,812 kilometres. Earth-like planets capable of supporting life are found only in a star's habitable zone, a region around a star where the surface temperature of a planet is suitable for liquid water.