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 by including the search for migrating extraterrestrial civilizations.
For example, extraterrestrial civilizations may leave their home planetary systems when faced with existential threats. One of the ways to do this is to travel on free-floating planets.
Free-floating planets can offer space and resources, as well as protection from space radiation, for very large populations embarking on interstellar travel.
It is technically impossible that huge starships—also called world ships—could offer the same.
Extraterrestrial civilizations may also use free-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 article, Romanovskaya discusses how extraterrestrial civilizations can travel on free-floating planets that are bypassing their home planetary systems, or they can travel on planet-like objects ejected from their planetary systems by dying host stars.
Alternatively, extraterrestrial civilizations can use propulsion systems and gravity assist events to convert objects equivalent to our Sedna in the Oort cloud into an interstellar mode of transportation.
Romanovskaya notes that with little starlight reaching free-floating planets, aliens could use controlled nuclear fusion as a power source, and could live in subterranean habitats and oceans to shield themselves from space radiation.
That would also prepare them for the colonization of oceans in planetary systems.
Upon their approach to planetary systems, the aliens could transfer from their free-floating planets to selected Oort cloud objects which would carry them inland and to the major planets of the systems to be colonized.
Or, planetary systems could capture those free-floating planets. Then, aliens would colonize such planetary systems.
To discover aliens on free-floating planets, Romanovskaya proposes looking for certain technological signatures—electromagnetic emissions produced by alien technologies on and around free- floating planets—and, in some cases, finding matching signs of terraforming that may be indicative of a process. of colonization.
If astronomers detect technological signatures produced on a free- floating planet without detecting the planet itself, they could 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 the aliens sent a Wow! of 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 search for free-floating planets along the lines of observations of unusual and potentially man-made signals from space.
Romanovskaya proposes that there may be a very small chance that in the last few billion years, free-floating planets with intelligent extraterrestrial species have traveled in 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 free-floating planets and searching for a new home.
Romanovskaya recommends that the search for such space travelers, the search for migrating extraterrestrial intelligence (SMETI), should be part of our search for intelligent life in the universe.