Hmmm ... I don't know. The Prophet is mentioned in the Quran as a mercy for the worlds. That implies his greatness beyond earth. Just a thought.
But I hadn't realised I was on the money about aliens! :)
EDIT: What I mean is, human beings in general are one thing. The Prophets may not count in this instance. So we could still be outdone by aliens, or as Jawaid says, by other forces of nature even on earth.