Answer:
It depends on what the abilities and technology of the aliens are.
Explanation:
Aliens could have any sort of tech or abilities. Such as, some aliens could have chameleon DNA. This would allow them to blend in, and thus make it to where they would be here, but we just wouldn't know. The same thing goes for if they have cloaking devices or such. Also, it depends on how advanced they were. If they were just now in existence, they probably wouldn't be advanced enough to hide. Also, we must consider what our planet is like. In "War of the Worlds", disease and microscopic organisms kill off all of the Martians. The same would happen to aliens landing, unless they somehow had some immunity thanks to their genetics. Also, we must consider diet. What if our world doesn't hold their kind of prey? In that case, I doubt the aliens would be on this planet. There are many other factors that could be listed, however, I will just leave it to you to decide. I just believe that it depends.
