Arrange comet and planet study (11)
I believe the answer is:
contemplate
'study' is the definition.
(I know that study can be written as contemplate)
'arrange comet and planet' is the wordplay.
'arrange' indicates anagramming the letters.
'and' is a charade indicator (letters next to each other).
'comet' put after 'planet' is 'planetcomet'.
'planetcomet' is an anagram of 'CONTEMPLATE'.
(Other definitions for contemplate that I've seen before include "Look at thoughtfully" , "Intend" , "Think seriously" , "Ruminate on" , "Consider" .)