Smooth attempt to come across a Martian, perhaps? (9)
I believe the answer is:
planetary
'martian perhaps?' is the definition.
'smooth attempt to come across a' is the wordplay.
'smooth' becomes 'plane' (plane can mean to smooth down).
'attempt' becomes 'try' (synonyms).
'to come across' indicates putting letters inside.
'try' going around 'a' is 'tary'.
'plane'+'tary'='PLANETARY'
(Other definitions for planetary that I've seen before include "Of Mars and Uranus, say" , "Relating to bodies in the solar system" , "Of any heavenly body moving round the sun" .)