Cosmic Hitchhikers: Advanced Aliens Might Use Free-Floating Exoplanets for Interstellar Travel

by johnsmith

In a new paper published in the International Journal of Astrobiology, Houston Community College researcher 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 as well as their technologies; she also proposes possible technosignatures and artifacts that may be produced by extraterrestrial civilizations using free-floating planets for interstellar migration and interstellar colonization, as well as strategies for the search for their technosignatures and artifacts.

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

An 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 nomad planets, they may have a liquid ocean under a thick atmosphere or an ice layer, and some of them may host simple life forms, especially in subsurface environments.

Free-floating planets can become unbound thanks to various common processes. For example, they may be produced in the process of ejection of fragments from a protoplanetary disk when it is perturbed.

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

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

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

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

“That would also prepare them for colonization of oceans in planetary systems.”

Because free-floating planets cannot sustain their oceans forever and more exploration opportunities exist in planetary systems, extraterrestrial civilizations would ride free-floating planets to reach and colonize planets orbiting stars.

Upon their close approach to planetary systems, the extraterrestrials could transfer from their free-floating planets to selected Oort-cloud objects of the planetary systems that would carry them inwards and towards the major planets of the planetary systems.

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

Then, the extraterrestrials would colonize the planetary systems.

To discover extraterrestrials riding free-floating planets, Romanovskaya proposes to search for certain technosignatures and, in some cases, for matching signs of terraforming in a few planetary systems potentially indicating that one civilization riding free-floating planets could colonize them.

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

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

Forty-five years later, they continue hypothesizing why the signal was detected only once.

“If extraterrestrials sent the Wow! signal from an undetected free-floating planet and the planet moved away from the line of observations, then the Wow! signal would not be detected along that line of observations again,” Romanovskaya said.

“Thus, astronomers should search for free-floating planets along the lines of observations of unusual and potentially artificial signals coming from space.”

“There may be a very small chance that over the last few billions of years, free-floating planets with extraterrestrial intelligent species may have traveled in our stellar neighborhood.”

“I recommend 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.”


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

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