Planetoids (9)
I believe the answer is:
asteroids
'planetoids' is the definition.
('asteroid' can be a synonym of 'planetoid')
This is the entire clue.
(Other definitions for asteroids that I've seen before include "Do satires address small planets?" , "lumps of rock" , "Small planets orbiting the sun" , "Small celestial bodies that move around the sun" , "Heavenly bodies" .)