Marcus Kirkwood surveys asteroids for a living. They're rocks. He's good at rocks.
Asteroid 2031 AV7 is not a rock.
It has a planar ceiling. Interior walls at precise 95-meter intervals. An atmosphere maintained at 12 degrees Celsius by systems that have been running continuously for 4.1 million years. And a door — hinged, engineered, sized for something approximately human height — that opens with four kilograms of pressure.
Marcus is a geologist. He has a drill, a paper notebook, and forty-two days before his mining company expects a platinum survey. He is not qualified for this.
He opens the door anyway.
Dead Orbit is a first contact story about loneliness, precision, and what the universe left for us in a rock — told through the field logs of a twice-divorced contract geologist who came to the asteroid belt looking for platinum and found everything else instead.