Halenn is a terrestrial exoplanet orbiting the K5V star HD 291782, located 4.3 light-years from the supermassive black hole NGC-7142α. The planet is notable both for its native sapient species, the crystalline-boned Halennites, and its unique astronomical "mirror" relationship with the planet Telenn across NGC-7142α's event horizon.
Halenn is a terrestrial world with 1.3 times Earth's radius and 1.8 times its mass, resulting in surface gravity of 1.1g. Its atmosphere is nitrogen-oxygen based, with a higher percentage of noble gases than Earth-standard. The planet completes an orbit of HD 291782 every 298 standard days and has a rotational period of 27 hours.
The planet's proximity to NGC-7142α results in unique gravitational effects that manifest in its geological activity. Regular gravitational waves from the black hole create predictable patterns in Halenn's tectonic movements, leading to the formation of distinctively symmetrical mountain ranges and ocean basins.
The Halennites are a humanoid species notable for their crystalline skeletal structure, which exhibits natural piezoelectric properties. This unique biology allows them to perceive gravitational waves directly through their bone structure, an ability that played a crucial role in their early scientific development. Adult Halennites typically stand 2.1 metres tall and display a natural bioluminescence that intensifies during periods of strong gravitational wave activity.
The planet's position relative to NGC-7142α has made it a crucial location for gravitational research. The Halenn Observatory Complex, established in 12-3789, hosts the largest collection of gravitational wave detection equipment in the known galaxy. The facility has been instrumental in studying the "mirror effect" between Halenn and Telenn, contributing significantly to current understanding of black hole physics.