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 "A space-traveller", "Space traveller", "shooting star", "falling star", "Glowing body entering atmosphere", "Streak of light in the night sky", "A remote sort of heavenly body", "Body falling from space", "Body entering earth's atmosphere" and "Remote sort of heavenly body".)