In an article published in the International Journal of Astrobiology, scientist Irina K. Romanovskaya proposes that the search for extraterrestrial intelligence (SETI) may have a better chance of success if it includes the search for migratory extraterrestrial civilizations.
For example, extraterrestrial civilizations may leave their home planetary systems when faced with existential threats. One way they do this is by traveling on floating planets.
Floating planets could offer space and resources, as well as protection from space radiation, for very large populations embarking on interstellar travel.
It is technically impossible for huge starships – also called worldships – to offer the same.
Extraterrestrial civilizations may also use floating planets to send biological or post-biological species to study interstellar space, stars, and planetary systems.
Or to establish their colonies in various planetary systems to preserve and expand their civilizations, even before they face existential threats on their home world.
In her paper, Romanovskaya discusses how extraterrestrial civilizations may travel on floating planets that are orbiting their home planetary systems, or they may travel on planet-like objects ejected from their planetary systems by dying host stars.
Alternatively, extraterrestrial civilizations could use propulsion systems and gravity assist events to convert objects equivalent to our Sedna in the Oort cloud into a means of interstellar transportation.
Colonization
Romanovskaya notes that with little starlight reaching floating planets, aliens could use controlled nuclear fusion as a power source and could live in underground habitats and oceans to protect themselves from space radiation.
This would also prepare them for ocean colonization in planetary systems.
Upon their approach to planetary systems, the aliens could transfer from their floating planets to selected objects in the Oort cloud, which would transport them to the interior and main planets of the systems to be colonized.
Or the planetary systems could capture these floating planets. Then, aliens would colonize these planetary systems.
To detect aliens on floating planets, Romanovskaya proposes looking for certain technological signatures — electromagnetic emissions produced by alien technologies on and around floating planets — and, in some cases, finding corresponding signs of terraforming that could be indicative of a process of colonization.
Wow signs
If astronomers detect technosignatures produced on a free-floating planet without detecting the planet itself, they may misinterpret the origin of the signals.
For example, on August 15, 1977, astronomers detected the famous Wow! in the constellation Sagittarius. Forty-five years later, scientists continue to hypothesize why the signal was detected only once.
According to Romanovskaya, if aliens sent a Wow! from an undetected floating planet and the planet moved away from the line of observations, the signal would not be detected again along that line.
Therefore, astronomers should look for free-floating planets along the lines of observations of unusual, potentially man-made signals from space.
Romanovskaya proposes that there may be a very small chance that in the last billion years, free-floating planets with intelligent extraterrestrial species have traveled through our stellar neighborhood, and discusses different ways to search for their artifacts in the solar system and on nearby planetary systems.
Somewhere in space today, hundreds of light years from Earth or closer, migratory intelligent biological species or artificially intelligent post-biological beings may be traveling on floating planets and searching for a new home.
Romanovskaya recommends that the search for such space travelers, the search for migratory extraterrestrial intelligence (SMETI), should be part of our search for intelligent life in the universe.
