Scientist explains why alien civilizations may be trapped on their home worlds

A theory by astrophysicist Frank Drake has been revisited by researchers who are now saying perhaps Drake didn't take his theory far enough.

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Frank Drake's theory, called the "Drake equation," explored the possible reasons why Earth has been contacted or discovered any evidence of alien life. The equation takes many factors into account, such as the discovered number of star systems, planets orbiting those stars, the rate of star formation, and the percentage of planets that would have the necessary conditions for life to exist for a prolonged amount of time.

However, a new study published in the Journal of the British Interplanetary Society penned by Elio Quiroga Rodríguez, a professor at the Universidad del Atlántico Medio in Spain, took the Drake equation and said that two possibilities should be included. The first is alien civilizations on planets that are larger than Earth, which would require more thrust to leave the gravitational pull of the planet.

Quiroga says if the planet's gravity was intense, these alien civilizations "would not be able to leave the planet using any conceivable amount of fuel, nor would a viable rocket structure withstand the pressures involved in the process, at least with the materials we know."

The second factor to add to the Drake equation is planets that are entirely constituted with liquids such as water or methane. Alien civilizations that develop within these liquid planets wouldn't need to develop long-range telecommunication devices, as sound signals can be heard hundreds of miles away through the liquid.

"In an underwater world imbued into a fluid, such as water or liquid methane, where sound signals can be heard hundreds of kilometers away, communication between individuals could be feasible without the need for communication devices," Quiroga explained in the paper. "Telecommunications technology might never emerge on such a world, even though it could be home to a fully developed civilization."

Both of these new possibilities led Quiroga to coin the new term "fishbowl worlds".