Shortly after Ryland and Dr. Lokken first meet in chapter 8, they argue about the underlying explanation for the observed similarities between terrestrial life and Astrophage. Lokken confidently declares that the two life-forms independently evolved to depend upon water (a not-so-subtle dig at Ryland’s “infamous” paper in which he suggested that water is not required for life to evolve). Ryland, however, argues that Earth life and Astrophage, with their similar mitochondria and other shared biological features, must be the result of panspermia.

Panspermia refers to the hypothesis that life is distributed throughout the cosmos and can be transported between worlds by mechanisms including comets, asteroids, and dust particles. This is a contentious idea and many varieties of panspermia have been proposed over the years.

The European Space Agency’s EXPOSE facility on the International Space Station provided opportunities for research into astrobiological questions, including whether organisms could remain viable in space long enough to hypothetically populate another world. Biological samples were exposed to the vacuum (and high radiation environment) of space; some of the microorganisms tested with EXPOSE survived over a year of these harsh conditions. In an earlier beanbag, we also discussed concerns around the related idea of planetary protection and how scientists work to reduce the possibility of contaminating other worlds with terrestrial microbes.

While the suggestion that life itself began elsewhere in the cosmos and “seeded” Earth is considered fringe, pseudo-panspermia is a more widely accepted idea. Pseudo-panspermia instead refers to the idea that organic molecules may have originated in space before being transported to Earth— the delivery of life’s precursors rather than the transport of life itself.

We have known for decades that Martian meteorites sometimes land on Earth’s surface, the result of forcefully ejected material from large impacts on our neighboring planet. There also exists some evidence for a period of heavy bombardment by asteroids in the earliest days of Earth’s history, though the details, cause, and timing of this possibility are still debated.

Material from asteroid Bennu returned to Earth in 2023 by NASA’s OSIRIS-REx mission was found to contain 14 of the 20 amino acids required for life and all 5 nucleobases used in DNA and RNA. According to a NASA press release from early 2025, “The findings do not show evidence for life itself, but they do suggest the conditions necessary for the emergence of life were widespread across the early solar system, increasing the odds life could have formed on other planets and moons.” The earlier mission Stardust returned a sample of Comet Wild 2 to Earth; organic compounds, some including biologically useful nitrogen, were detected.

Regardless of its controversial stance within the scientific community, panspermia has found a home in imaginative science fiction works. The Star Trek: The Next Generation episode ‘The Chase’ and the anime Neon Genesis Evangelion take the idea even further, exploring examples of deliberately directed panspermia.