The Big Sun of Mercury

Lucky Starr and the Big Sun of Mercury was written in 1955, when it was believed that Mercury was tidally locked to the Sun. A character notes that there are places on Mercury's sunside where it is hot enough to melt lead and boil sulfur, while the nightside is the only planetary surface in the Solar System that never sees the Sun. Most of the novel's action takes place in and around an astronomical observatory located at the planet's north pole, where libration results in a half-mile movement of the terminator. The observatory was built fifty years before on the site of a mining complex, which has since been abandoned.