Vehicle on Mars (5)
I believe the answer is:
rover
'vehicle on mars' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rover that I've seen before include "One who wanders about" , "A vagrant" , "Vehicle driven remotely over extraterrestrial terrain" , "Wanderer, archery mark" , "Itinerant person" .)