Mars rover. Artwork of a small rover vehicle exploring a graben on the surface of Mars. A large dust storm is approaching at upper right. A graben is a type of rift valley. Mars has been the subject of intense scrutiny for centuries. Towards the end of the 19th century, it was a popular belief that Mars might be inhabited. Space probes and rovers such as this have tested many soil samples, but so far there has been no evidence to support the view. A manned mission to Mars is planned, and there has even been talk of setting up permanent colonies there.