Planet discussed as having potentially been a twin to Earth with life support under different conditions, becoming a hellhole relatively recently in planetary timescales.
Mentions (1)
"Like the cosmic equivalent of finding out you were meant to have a sibling a year younger than you who miscarriaged. I wonder if space exploration would have moved faster if we knew of a planet that could either support life or had life on it pretty much right next door. What sort of species could h"