If gods were aliens, what ghosts could be?

I'm not specifically talking about ghosts in modern-era, those which are captured on videos/photos. I read that ancient people used to believe in ghosts. They believed in gods too.

Ancient Astronaut theories suggests that gods were extra terrestrial beings who visited earth. If so, what could possibly be ghosts? Were they too aliens?

What has been discovered about this so far? I'm being curious.

NOTE: This question was in Skeptics before but there they recommended me to post it here. I'm not sure that this is the right place or not. Suggest me if not.