Location from Project Hail Mary by Andy Weir
The CO2-choked planet where Astrophage breed and their natural predator was waiting — the answer to everything, orbiting a star no one was watching.
Adrian is Tau Ceti's equivalent of Venus: a CO2-rich planet that serves as the local Astrophage breeding ground. Astrophage are attracted to carbon dioxide spectral lines, migrate to CO2-rich planets, breed in the upper atmosphere using carbon from CO2, and then return to the star with their offspring to feed. This is why Adrian matters: it's the nursery. But Adrian also hosts Taumoeba — an amorphous microorganism that preys on Astrophage, enveloping and killing them. This predator-prey relationship is why Tau Ceti's Astrophage population stays controlled while other stars are being devoured. Adrian's atmosphere is a war zone at the microscopic level, and the combatants don't care that two civilizations' survival depends on the outcome.
A massive planet — 3.93 times Earth's mass — with a thick, opaque atmosphere of 91% carbon dioxide, 7% methane, and 1% argon. The surface is invisible from orbit through the dense atmosphere. Diameter of 10,318 kilometers. From space, it looks like a dull, brownish sphere — nothing about its appearance suggests it holds the key to saving two civilizations.
Also known as: Tau Ceti e, Adrian