Class K: Adaptable planets represent an unfortunate part of
planetary development: a failed world. Over the course of a
terrestrial planet's long and arduous evolution (from Class E to
Class F to Class G), something, somewhere goes wrong, and the
blossoming young planet fails to reach its full potential. Volcanic
activity slows to a halt, the tenuous atmosphere begins to disperse,
any liquid on the surface evaporates, and the rocky young world
essentially dies.

Though rare, simple single cell organisms can still thrive on these
barren worlds, but more complex forms of life never evolve. As a
result, Class K planets are easily colonized via the use of pressure
domes, and are often prime candidates for terraforming. Average
temperatures are quite cold by humanoid standards, but a warm
summer day on a terraformed Class K planet might creep as high as
20°C.