Interior of planet here, almost unearthly (8)
I believe the answer is:
ethereal
'unearthly' is the definition.
(thesaurus)
'interior of planet here almost' is the wordplay.
'interior of' indicates a hidden word.
'ETHEREAL' is hidden within 'planet here almost'.
(Other definitions for ethereal that I've seen before include "'Extremely delicate, almost not of this world (8)'" , "Having great lightness and delicacy" , "Exquisite - as light as air" , "'Delicate, heavenly (8)'" , "Sublime" .)