Aliens can survive without a home planet.
Aliens don't need a home planet to survive
Experts have suggested that the little green men could be floating around the universe inside a thin hard shell rather than living in a specific part of the solar system.
Astrophysicist Paul Sutter told Space.com: "What if we dropped the 'terrestrial' from 'extraterrestrial'?
"At first glance planets seem like the ideal locations to find life. The only place life is known to exist is Earth.
"Our planet has a deep gravitational well that keeps everything in place and a thick atmosphere that keeps surface temperatures in the right ranges to maintain liquid water.
"It's from this basic set-up that we organise our searches for life elsewhere in the universe."
The American boffin explained that scientists are beginning to challenge this "basic assumption" and believe it is possible to "construct an environment that allows life to thrive without a planet".
Sutter is adamant that the theory isn't "as crazy as it sounds".