The further an investigation gets from testable science, the more speculative it becomes. How many inferences and ad hoc stories does it take before a scientific endeavor becomes science fiction? Two recent proposals from professional cosmologists step squarely across the boundary between conjecture-containing science and just plain conjecture.

Some scientists refer to certain dust and debris clouds in galaxies as star “incubators” because they think stars form naturally within them. But since the formation of a star from a compacted cloud would take far too long to observe even in many lifetimes, many references to stellar nurseries rely on circumstantial evidence and naturalistic reasoning.

The Wide Area Search for Planets (WASP) project has discovered a planet that orbits backward, against the rotational direction of its star. Methodological naturalists think collisions or near-collisions are the causes of unusual cosmic phenomena like this.

The ongoing quest to find life in space has failed to yield any supportive evidence that life exists outside the earth. To prop up the idea of distant spontaneous life formation, some scientists are willing to settle for science fiction. One Serbian astrobiologist has taken cues from evolutionary paleontology—and maybe even from comic books.