Aliens haven’t visited Earth because they’re trapped by gravity on their own planets – or at least, that’s the conclusion reached by a coalition of European astronomers.
As Cordis reports, scientists have long been looking for, and finding, so-called “exoplanets” – that is, planets outside of our known solar system. To date, they’ve found about 2,000, according to Sun.org. Of course, many of them are inhospitable to life, being composed of gas, or being too close to, or too far away from, their own suns to be in the so-called “Goldilocks zone” where life is possible.
Of the ones that are both solid and in the Goldilocks zone, however, there’s another problem: they’re too big. Specifically, they’re larger than Earth, and indeed, some are believed to be the size of Jupiter (the largest planet in our own solar system) or even bigger.
That creates a major problem for space exploration: namely, that gravity on those planets is so strong that alien spacecraft simply can’t get off the ground and explore space.
Michael Hippke, an independent researcher affiliated with the Sonneberg Observatory in Germany, says that the gravity on a larger-than-Earth exoplanet will keep its inhabitants grounded in the most literal possible sense.
“On more-massive planets, spaceflight would be exponentially more expensive.”
— Scientific American (@sciam) May 4, 2018
In fact, says Hippke, alien civilizations on super-Earth exoplanets may even be technologically behind us due to their own limitations.
“Such civilizations would not have satellite TV, a moon mission or a Hubble Space Telescope.”
Here on Earth, the biggest reason space travel is so expensive is gravity. Simply put, getting a craft into space is the expensive part, what with all of the fuel expended in getting beyond the surly bonds of Earth. Now imagine that problem magnified by, for example, Kepler-20b, which is 70 percent wider than Earth and 10 times more massive. Hippke calculates that it would cost the alien civilization 2.4 times what we spend on getting a spacecraft into orbit.
Of course, perhaps an alien civilization has evolved beyond money and can launch spacecraft into space without having to worry about budgets. Or perhaps they’ve evolved beyond having to use chemical-based fuel like we do, and can instead launch spacecraft via nuclear power or warp drives, or even something else entirely. We’ll likely never know.
There’s also another big problem in space travel: space itself. Even if we could figure out how to travel at, or beyond, the speed of light (which is impossible given our current understanding of the laws of physics), space is so vast that even light-speed travel is not fast enough. The nearest star to us, excluding the Sun, is 4.3 light years away, meaning a manned mission to Proxima Centauri would take 4.3 years just to get there, even if we could travel at light speed. Kepler 20-b, mentioned in the previous paragraph, is 950 light years away.