Large asteroid sequence broadcast (5)
I believe the answer is:
ceres
'large asteroid' is the definition.
'sequence broadcast' is the wordplay.
'sequence' becomes 'series' (I've seen this before).
'broadcast' shows a homophone (sound like) (how the word might sound on the radio or TV).
'series' sounds like 'CERES'.
(Other definitions for ceres that I've seen before include "The largest asteroid" , "She fills granaries" , "chief of agriculture" , "Roman goddess of corn" , "Roman goddess; dwarf planet" .)