Body in space to travel over time (5)
I believe the answer is:
comet
'body in space' is the definition.
(I've seen this before)
'travel over time' is the wordplay.
'travel' becomes 'come' (coming is a kind of travelling).
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'time' becomes 't' (abbreviation).
'come'+'t'='COMET'
'to' is the link.
(Other definitions for comet that I've seen before include "High-flyer" , "Early jetliner" , "Celestial orbiter" , "Heavenly visitor" , "Object in space with bright centre and long hazy tail" .)