Of course there are aliens under the earth, they're called demons and fallen angels. Some are in Tartarus right now (2 Peter 2:4, "For if God didn’t spare angels when they sinned, but cast them down to Tartarus..."). They sinned in Genesis 6 and spawned the Nephilim. They didn't come from other planets, but from another dimension and their master is satan. The whole "alien" thing is a myth thought up to deceive man. Don't believe the lie.