...damages planet (4)
I believe the answer is:
mars
I believe this is a double definition.
'damages' is the first definition.
(marring is a kind of damaging)
'planet' is the second definition.
(Mars is an example)
(Other definitions for mars that I've seen before include "Injures - god of war" , "Damages - planet" , "Ruins" , "blights" , "RS [RED STAR] (not technically)" .)