Friend supports new planet being discovered, of course (9)
I believe the answer is:
naturally
'of course' is the definition.
('naturally' can be a synonym of 'of course')
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for naturally that I've seen before include "it goes without saying" , "as you might expect" , "as normal" , "without medicine" , "In an artless way" .)