A new article in the Journal of the British Interplanetary Society examines the idea of civilizations on other worlds and the factors that govern their ability to explore their solar systems. Its title is "Introducing the Exoplanet Escape Factor and the Fishbowl Worlds (Two conceptual tools for the search of extra-terrestrial civilizations)." The sole author is Elio Quiroga, a professor at the Universidad del Atlántico Medio in Spain.

We have no way of knowing if other extraterrestrial intelligences exist or not. There's at least some possibility that other civilizations exist, and we're certainly in no position to say for sure that they don't. The Drake equation is one of the tools we use to talk about the existence of ETIs. It's a kind of structured thought experiment in the form of an equation that allows us to estimate the existence of other active, communicative ETIs. Some of the variables in the Drake equation are the star formation rate, the number of planets around those stars, and the fraction of planets that could form life and on which life could evolve to become an ETI.

In his new research article, Quiroga comes up with two new concepts that feed into the DE: the exoplanet escape factor and fishbowl worlds.

Planets of different masses have different escape velocities. Earth's escape velocity is 11.2 km/s (kilometers per second), which is more than 40,000 km/h. The escape velocity is for ballistic objects without propulsion, so our rockets don't actually travel 40,000 km/h. But the escape velocity is useful for comparing different planets because it's independent of the vehicle used and its propulsion.

Super-Earths have much greater masses and much higher escape velocities. While there's no exact definition of a super-Earth's mass, many sources use the upper bound of 10 Earth masses to define them. So, an ETI on a super-Earth would be facing a different set of conditions than we do here on Earth when it comes to space travel.