Astronomical spoils! (4)
I believe the answer is:
mars
'spoils' is the definition.
('mar' can be a synonym of 'spoil')
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for mars that I've seen before include "Possibly pollutes" , "Holst's Bringer of War" , "Ruins" , "part of suite" , "world" .)