Location from Project Hail Mary by Andy Weir
The one star in the neighborhood that isn't being eaten — and the twelve-light-year question that two civilizations bet everything on answering.
Tau Ceti is an anomaly wrapped in a question. Every star within eight light-years of Sol is infected with Astrophage and dimming. Tau Ceti is not. This single fact — one healthy star surrounded by sick ones — is what makes the Hail Mary mission possible and necessary. Something in this system kills Astrophage, or prevents them from thriving, or controls their population. Finding that something is the entire mission. The answer turns out to be Taumoeba: a natural predator living on Adrian that keeps the local Astrophage population in check. The system is a battlefield between microorganisms that humans and Eridians stumbled into, and the solution to both civilizations' extinction was growing on a planet no one had ever heard of, twelve light-years from anywhere that mattered — until suddenly it mattered more than anywhere else in the universe.
A star system twelve light-years from Earth. Tau Ceti burns steadily at full luminance while every neighboring star dims under Astrophage infection. The system includes multiple planets, most notably Adrian (Tau Ceti e), a CO2-rich world where Astrophage breed — and where their natural predator was waiting to be found.
Also known as: Tau Ceti, The Tau Ceti System