Planet extremely hazy and boggy (6)
I believe the answer is:
marshy
'boggy' is the definition.
('marshy' can be a synonym of 'boggy')
'planet extremely hazy' is the wordplay.
'planet' becomes 'mars' (Mars is an example).
'extremely' suggests removing the centre.
'hazy' with its centre removed is 'hy'.
'mars'+'hy'='MARSHY'
'and' is the link.
(Other definitions for marshy that I've seen before include "treacherous underfoot" , "(Of soil) soft and wet" , "(Of land) waterlogged" , "Like swamps" , "Soggy" .)