Cosmic hitchhikers: Advanced aliens could use free-floating exoplanets to travel between stars


In a new paper published in the International Journal of Astrobiologyresearcher at Houston Community College Irina Romanovskaya proposes that free-floating planets can be used as a means of interstellar travel for large groups and populations of intelligent biological and post-biological species and their technologies; it also offers possible technosignatures and artifacts that may be produced by extraterrestrial civilizations using floating planets for interstellar migration and interstellar colonization, as well as strategies for finding their technosignatures and artifacts.

Artist’s impression of a free-floating exoplanet. Image credit:

Free-floating planets are planetary-mass objects that are not gravitationally bound to their stars.

Also known as rogue or nomadic planets, they can have a liquid ocean under a thick atmosphere or a layer of ice, and some of them can host simple life forms, especially in subterranean environments.

Floating planets can break up through various common processes. For example, they can be produced during the process of ejecting fragments from a protoplanetary disk when it is disturbed.

These objects can also be ejected by interactions with another star or by scattering interactions in a multiplanetary system.

In her paper, Romanovskaya discusses how extraterrestrial civilizations can hitchhike on free-floating planets that pass through their home planetary systems, or they can ride planet-like objects ejected from their planetary systems by dying host stars.

Or, extraterrestrial civilizations may use propulsion systems and gravity assist events to convert the Sedna-like Oort Cloud objects of their planetary systems into free-floating planets and ride them among the stars.

“With little starlight reaching floating planets, extraterrestrials could use controlled nuclear fusion as an energy source, and they could inhabit the subterranean habitats and oceans of floating planets to be shielded from space radiation,” Romanovskaya said.

“It would also prepare them for ocean colonization in planetary systems.”

Because floating planets cannot sustain their oceans forever and there are increasing opportunities for exploration in planetary systems, extraterrestrial civilizations would ride floating planets to reach and colonize planets orbiting planets. stars.

During their close approach to planetary systems, extraterrestrials could transfer from their floating planets to selected Oort cloud objects of the planetary systems which would transport them inward and to the major planets of the planetary systems.

Or, planetary systems could capture such free-floating planets.

Then the extraterrestrials would colonize the planetary systems.

To discover aliens riding floating planets, Romanovskaya suggests looking for certain technosignatures and, in some cases, corresponding signs of terraforming in a few planetary systems potentially indicating that a civilization riding floating planets could colonize them.

If astronomers detect technosignatures produced on a floating planet without detecting the floating planet itself, they may misinterpret the origin of the technosignatures.

For example, on August 15, 1977, astronomers detected the famous Wow! signal in the constellation of Sagittarius.

Forty-five years later, they keep making assumptions why the signal was detected only once.

“If aliens sent the Wow! signal of an undetected floating planet and the planet moved away from the line of sightings, then the Wow! the signal would no longer be detected along this line of sightings,” Romanovskaya said.

“Thus, astronomers should look for free-floating planets in the direction of sightings of unusual and potentially man-made signals from space.”

“There may be a very small chance that over the past billion years, free-floating planets with extraterrestrial intelligent species have traveled through our stellar neighborhood.”

“I recommend that the search for such space travelers – the search for migrating extraterrestrial intelligence (SMETI) – be part of our search for intelligent life in the Universe.”


Irina K. Romanovskaya. Migration of extraterrestrial civilizations and interstellar colonization: implications for SETI and SETA. International Journal of Astrobiology, posted on April 28, 2022; doi:10.1017/S1473550422000143


Comments are closed.