Mysterious "almost perfectly circular" sand dunes have been spotted on Mars by cameras on a NASA spacecraft, leaving scientists scratching their heads.
While sand dunes may be quite common on Mars, it is strange for them to form circles which are nearly exact, said geologist Alfred McEwen, who has been examining the photo from NASA's Mars Reconnaissance Orbiter (MRO).
The shapes were spotted by the HiRISE camera, the most powerful ever sent to another planet which is on NASA's MRO, as scientists were examining how frost thaws at the end of a Martian winter.
