Ruins something heavenly (4)
I believe the answer is:
mars
'ruins' is the definition.
(to mar is to ruin or 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 "Fourth rock from the Sun" , "Fourth planet from the Sun" , "Holst's Bringer of War" , "Roman war god; planet" , "Ruins" .)