CS Lewis addressed this question both in his Space Trilogy and in an essay. His hypothesis is that God could have created many different sentient beings, but because of the Fall, earth is "quarantined" and thus out of contact.
Lewis might be onto something, but I don't think "quarantined" is quite the right word:
"CS Lewis addressed this question both in his Space Trilogy and in an essay. His hypothesis is that God could have created many different sentient beings, but because of the Fall, earth is "quarantined" and thus out of contact."