Esoterra

Esoterra is a fictional planet featured in the science fiction novel "The Mote in God's Eye" by Larry Niven and Jerry Pournelle. It is the homeworld of the Moties, an alien species encountered by humanity. Esoterra is described as a tidally locked planet, meaning one side perpetually faces its star, while the other is in eternal darkness. This results in extreme environmental conditions. The habitable zone for the Moties exists in a narrow twilight band between these two extremes.

The planet's geography is characterized by intense radiation on the starward side and extreme cold on the dark side. The Moties have adapted to survive in this challenging environment, developing a complex social structure and advanced technology. Their civilization has evolved to manage the scarcity of resources and the constant threat of environmental instability. Esoterra's unique conditions have shaped the Moties' biology, psychology, and their approach to interstellar relations. The novel explores the implications of encountering such an alien civilization and the potential dangers and opportunities that arise from such contact, with Esoterra serving as the backdrop for this pivotal moment in galactic history.