The idea of aliens has captured the imaginations of some and put terror into the hearts of others. The image of little green men descending from the sky to greet us with some strange alien culture does not cause so much fear as the idea of great metal behemoths falling from the sky to raze the human species from the surface of our world. But we must also root ourselves in reality. Have aliens ever landed on Earth? The answer is no. Aliens have not landed on our planet.
I suppose I must first define what aliens mean. It is easy to say that aliens might not have real visible bodies of mass and are just spirits floating through the universe, but then it’s possible that those spirits are passing through you every second with no effect, in which case, what do they matter to the argument? If the aliens are beyond our perception, then they are not germane to the argument. They are simply a constant.
By aliens, I’m speaking of life forms that exhibit six basic traits necessary to define life: reproduction, motion, metabolism, responsiveness to the environment, growth, and a defined lifespan. These traits are defining of life as we know it, so these are the traits defining life forms that we as life forms could interact with.
We have to consider the changes between two planets. Firstly is the distance. The closest terrestrial and possibly life bearing planet known to man is in the Gliese system over 10 light years away. Any living creature would have to spend a significant fraction of their lifespan in the ship, and that’s assuming they have near-light speed travel. Without the ability to travel near the speed of light they would spend millions of years in their ship, hurtling through space littered with micro meteors and other obstacles. Even if they arrived here, the planet would be vastly different from when they set out, so what would be the point?
Once the aliens arrived here, they would face a new set of challenges. Since they would require some form of cellular energy they would need to exchange gases, and if they needed any gas other then oxygen they would be in big trouble. Even in Earth life forms oxygen is poisonous in large amounts; imagine what it would be in Earth levels for a non-oxygen exchanging organism. Plus there is the issue of gravity: unless specifically designed for Earth, most craft would either collapse under its own weight or be blown over by a stiff breeze. The technical hindrances are enormous.
Some people may put forward the argument that aliens are all around us. They will point at the crop circles with clear foot imprints and point at the Bermuda Triangle through which thousands of ships pass unharmed each day. But the reason I brought up these points is that any species intelligent enough to figure out interstellar travel is smart enough to think ahead to what needs to be done there. If it was conquest these supposed aliens wanted, they would have conquered; if they wanted resources, they would have sucked the planet dry. But humanity remains unconquered and all our rocks seem in place, so it seems that any alien mission was a failure. Or, more likely, it just never happened at all.
