Unusually remote celestial body (6)
I believe the answer is:
Here is my best explanation:
'celestial body' is the definition.
(meteor is a kind of celestial body)
'unusually remote' is the subsidiary indication.
'unusually' indicates an anagram.
'remote' with letters rearranged gives 'meteor'.
(Other definitions for meteor that I've seen before include "Streak of light in the night sky", "Shooting star", "Remote (anag)", "It causes a streak of light in the night sky", "Small piece of matter in the solar system", "Remote sort of heavenly body", "Body falling from space", "A remote sort of heavenly body", "Remote type of heavenly body" and "Falling star".)