In the ongoing search for extraterrestrial intelligence, it’s easy to get discouraged at times, with all the accumulated evidence to explain why we don’t have contact with aliens throughout the vastness of the cosmos. Now, an astrophysicist from Germany has come up with another solid reason for the frustrating lack of contacts, and it makes a lot of sense when you think about it.
Michael Hippke, an independent researcher affiliated with the Sonneberg Observatory in Germany, says one of the challenges for alien civilizations looking to explore space would be generating enough momentum to escape the gravitational forces of their planets.
But wait a second, humans have developed the ability to launch spacecraft out of and through our Solar System in the last century, so why haven’t advanced extraterrestrial life forms pulled off the same trick?
The problem, according to Hippke, is the planets that these beings can call home. One type of planet may offer good prospects for the idea: Super-Earths are rocky exoplanets with significantly greater mass than Earth’s, which could provide denser atmospheres capable of protecting alien life from their surfaces.
There’s only one downside to this Super-Earth scenario, and it’s a problem. “On more massive planets, spaceflight would be exponentially more expensive,” Hippke said.
In his new research, Hippke calculated the amount of alien spacecraft that would be needed to escape the gravitational pull of super-Earths and even larger, more massive worlds. If conventional rocket fuel were being used, calculations show that it didn’t take long for the resource to go beyond “expensive” and into the impossible.
For a launch like the classic Apollo mission, a rocket taking off from a Super-Earth would need approximately 400,000 metric tons of fuel to take off, which, as Hippke writes in his paper, is likely a realistic limit for chemical rockets relative to cost constraints.
Because of this constraint, Hippke calculates chemical rocket launches using conventional fuel would be possible but impractical on super-Earths, but if the alien world were even larger and had a higher mass, you would need to start looking at alternative rocket propulsion, such as nuclear propulsion.
That’s because as worlds grow larger and their mass becomes larger, it gets to the point where chemical fuel would be almost ridiculously weak, where “a sizable fraction of the planet” in fuel quantities would need to be used for each launch, significantly limiting the number of possible flights on alien worlds.
Of course, we’re talking about extraterrestrials and it’s entirely possible that they could create immensely different alien technology to help them get out of the world, but until they do that and fly into our field of vision, at least we have another reasonable explanation for why we don’t know any aliens yet.
