Aliens could be having a hard time getting to Earth — or anywhere — because they physically can’t get off their home planets, a new paper suggests.

The new research conducted by independent scientist Michael Hippke, who is affiliated with the Sonneberg Observatory in Germany, finds that the gravity on super-Earth exoplanets could be inadvertently preventing alien life from lifting off in rockets to leave their planets. Hippke’s work, which can be found on the pre-print server ArXiv, focuses on super-Earths, or exoplanets higher in mass than Earth but lower than that of a gas giant like Neptune.

Hippke argues that intelligent alien civilizations probably use chemical rockets, vaguely similar to the ones we have here on Earth. But because the gravity on super-Earths is stronger than the gravity here on Earth, Hippke says that even if alien civilizations developed space programs, it’d be enormously difficult to create a rocket capable of launching through such a force.

Artist rendition of Kepler-186f, a Super Earth orbiting another star.
Artist's rendition of super-Earth Kepler-186f.

This is a seriously wild idea on top of some already far-out alien stuff. But as SETI senior astronomer Seth Shostak explains in NBC News, there are even more issues with Hippke’s hypothesis.

“Some of Hippke’s calculations seem to be in error, leading him to overestimate the challenges to space programs on super-Earths,” Shostak writes. “But even if stronger gravity delayed the inhabitants of these worlds from getting off their planet by 50 or 100 years, you have to ask: so what? Does that bump in the road matter more than the fact that the larger size of their planet would delay the laying of telegraph cables from one continent to another, or that long-distance transport would be slower, simply because the distances would be — well — longer?”

At this point, no one knows whether or not alien life exists on distant exoplanets. In the event that it does, Shostak argues that a denser atmosphere could incentivize more aviation development.

“Greater acreage might bring a wider diversity of animals, possibly producing intelligence sooner than happened on Earth,” he writes. “And one could expect more abundant natural resources on an oversized world.”

All of this is to say that there’s a lot of speculation going on here. Nothing is definite. This is not a confirmation of aliens but rather an exercise in thinking about what they might be like. If they are out there, hopefully aliens are working on coming to our planet rather than reading our bad tweets.