Deductions About A Planet

The Imperial Solar spaceship, HM Ganymede, remotely controlled by aliens, crashes on a planet in the Black Nebula. Approaching the planet, it is possible to see that its star is an old, burnt-out dwarf. Since planets form at an early stage of stellar evolution, it follows that the planet also is old. On the surface, rocks, vitrified when the star exploded before its collapse, are almost completely eroded, a process that takes millions of years. It follows that rotation has slowed, therefore that the night will be long and cold.

However, there is still a breathable albeit thin atmosphere, frozen water and vegetation. These can have survived only with artificial help. Therefore, the planet is inhabited - by the aliens that wrecked the ship.

Additional information provided by Donovan, who has had previous contact with the aliens:

the star is near the center of the nebula in a hollow where the dust is too thin to force the planet into the star. Further, the star shares the nebula's velocity and therefore remains in the hollow.

Quite an exotic setting, like many others imagined by Poul Anderson, such as the Sky Cave and the Cloud Universe, both encountered in later periods of the Technic History.