An extraordinary new study claims that there may be aliens out there who live on “super-Earths” that are trapped by their own intense gravity, making it just about impossible to ever venture out into space. Basically, scientists believe that many of the exoplanets out there that might be suitable for life are much larger than Earth, with diameters up to twice as large as they are on our own planet.

As a result, aliens would have a hard time breaking free of their planet’s gravity by using the chemical rockets that we rely on because it would take vastly more energy to do so. That means more fuel, which would also mean that the rocket would have to be even bigger to carry that extra payload, and the problem becomes magnified for this hypothetical alien species.

However, some question this hypothesis, pointing out that while it would be harder in this scenario, it wouldn’t necessarily be a lot harder. One writer noted that SpaceX’s Falcon Heavy rocket could be scaled up with relative ease. Still, it is an interesting thought experiment.

“Many rocky exoplanets are heavier and larger than the Earth, and have higher surface gravity,” the abstract states. “This makes space-flight on these worlds very challenging, because the required fuel mass for a given payload is an exponential function of planetary surface gravity, ∼ 3.3 exp(g0). We find that chemical rockets still allow for escape velocities on Super-Earths up to 10× Earth mass. More massive rocky worlds, if they exist, would require other means to leave the planet, such as nuclear propulsion.”