Until now, not a single such sign has been found, so scientists have to be content with only theories. Recently, Russian researcher Irina K. Romanovskaya suggested that extraterrestrial civilizations could be colonizing the galaxy without having starships.
This theory is that extraterrestrial civilizations can use the so-called free-floating planets – celestial objects with a mass of a planetary nature, but not connected by gravity with any of the stars.
The researchers note that creating a huge starship capable of carrying on board everything necessary for the crew in the right volumes is an incredibly expensive undertaking, which can take many years to create.
Orphan planets may have everything necessary for the existence of interstellar travelers. That is why scientists should turn their attention to free-floating planets.
But it’s far from a fact that such a celestial object will be near us in the near future. Therefore, it will not be possible to test the efficiency of the theory soon.