Just describe ghosts as some kind of sci-fi tech gone awry!
"We tried to beam back to our ship, but some freaky-deaky space storm did some shenanigans and now our molecules are floating around in a cloud. Help!"
A spectro-temporal entity, designated as 'Echo-1-alpha,' has been detected in the vicinity. This non-corporeal being is characterized by a persistent quantum flux anomaly, indicative of an unstable vortex in the space-time continuum.
Further analysis reveals a matrix of chrono-displaced energy patterns, which we're terming 'psi- waves.' These psi-waves are oscillating at a frequency of 3.14 terahertz, consistent with known manifestations of paranormal activity in subspace.
Reroute power to the deflector dish. Solves most problems. Failing that, reverse the polarity (even if it's not a charged particle, such as neutrons - apologies to the Third Doctor).
Feel free to object (I'm not saying this in any official mod capacity) but I'd say for now, first person to suggest a day's theme should get to call it.