Cultivate distant surface of Mars (4)
I believe the answer is:
farm
'cultivate' is the definition.
(I know that farm is a type of cultivate)
'distant surface of mars' is the wordplay.
'distant' becomes 'far' (similar in meaning).
'surface of' suggests taking the first letters.
The initial letter of 'mars' is 'm'.
'far'+'m'='FARM'
(Other definitions for farm that I've seen before include "Country workplace" , "Agricultural building" , "croft" , "Cold Comfort --" , "See 5" .)