Space traveller joins a gathering of editors (8)
I believe the answer is:
asteroid
'space traveller' is the definition.
(I've seen this before)
'gathering of editors' is the wordplay.
'gathering' becomes 'a' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'of' is an anagram indicator (the answer comes from or 'of' the letters).
'editors' anagrammed gives 'steroid'.
'a'+'steroid'='ASTEROID'
'joins a' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for asteroid that I've seen before include "Minor planet" , "looking like a star?" , "Small planet orbiting the Sun" , "Ceres, say" , "Bits of rock that move around the heavens" .)