Goddess moves Mars: it blocks Earth (7)
I believe the answer is:
artemis
'goddess' is the definition.
(Greek goddess)
'moves mars it blocks earth' is the wordplay.
'moves' is an anagram indicator.
'blocks' means one lot of letters goes inside another (inserted letters are blocked in).
'earth' becomes 'E'.
'mars'+'it'='marsit'
'marsit' anagrammed gives 'artmis'.
'artmis' placed around 'e' is 'ARTEMIS'.
(Other definitions for artemis that I've seen before include "Virgin" , "God" , "Greek huntress goddess" , "Twin sister of Apollo" , "Olympian figure" .)