Tenebra is a planet with an unusually dark, foggy atmosphere, orbiting the giant star Altair. It is also the homeworld of the Tenebran species. Tenebra's gravity is about three times that of Earth and the surface pressure approaches 800 atm. The Tenebran surface is notable for being exposed to daily temperatures close to the critical point of water. The atmosphere mainly consists of water vapor (parts of which liquefy every night), hot enough to melt the silicate minerals of the crust; giving the planet an ever-changing geography which is nevertheless inhabited by numerous species of fauna, flora and floating organisms; biologically adapted to survive in these conditions. Overall the Tenebran surface environment most closely resembles that of Earth's deepest oceanic abysses in some ways (extreme temperature and pressure, and darkness).