Fear last couple is missing, so returns to moon (6)
I believe the answer is:
phobos
'to moon' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for phobos that I've seen before include "heavenly body" , "Planetary moon" , "another world" , "Moon of Mars" , "Satellite of Mars" .)