Go round passing remarks about earth's core (5)
I believe the answer is:
orbit
'go round' is the definition.
(I've seen this before)
'passing remarks about earth's core' is the wordplay.
'passing remarks' becomes 'obit' (obituary, report on someone's passing).
'about' is an insertion indicator.
'earth's core' becomes 'r' (I can't justify this - if you can you should believe this answer much more).
'obit' going around 'r' is 'ORBIT'.
Can you help me to learn more?
(Other definitions for orbit that I've seen before include "Particular environment" , "Go round" , "Sphere of action" , "Path eg of heavenly body" , "Circle in space" .)