Ariel orbits it (6)
I believe the answer is:
uranus
'ariel orbits it' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for uranus that I've seen before include "world" , "Planet of solar system" , "Seventh planet from the sun" , "Planet discovered by William Herschell in 1781" , "Planet discovered in 1781 by Herschel" .)