Aliens might be using rogue planets as spaceships

pcgamer.com:

According to a study published in the International Journal of Astrobiology(opens in new tab), aliens could use rogue planets—wandering worlds that have either been knocked from the system they originated in like a snooker ball by some gravitational event, or were formed externally—as alternatives to spacecraft. 

The study comes from a professor of physics and astronomy at Houston Community College named Irina Romanovskaya, who told Motherboard(opens in new tab) that, since rogue planets are hard to detect in the interstellar dark between systems, there may be a substantial number of them out there. «This increases the chance that some advanced extraterrestrial civilizations, if they exist, might hitch a ride on free-floating planets,» Romanovskaya said. «Which is why I call such hypothetical civilizations Cosmic Hitchhikers.»

While they wouldn't be drawing energy from a star like regular planets, apparently these nomad worlds could still be habitable. They might have subsurface oceans, atmospheres with enough hydrogen to preserve them, and enough residual core heat to provide energy for a substantial period of time.

Sounds like a great idea for a videogame, and indeed there have been games about rogue planets. Starquake, first released on the ZX Spectrum in 1985, had you trying to stabilize a rogue planet before it imploded, and Metroid Prime 2 was set on a rogue planet with a dark extradimensional twin, which is not a concept that has quite so much basis in science.

Romanovskaya's hypothesis is based on sounder principles: that rogue planets have advantages over spaceships like coming with their own resources and habitats, and not needing artificial gravity. They could also provide an escape for inhabitants of an aging