Potential openings to large caves have been spotted on the Martian surface. Glen Cushing, from the US Geological Survey (USGS) in Flagstaff, Arizona has reported on the findings, which he spotted in THEMIS (Mars Odyssey's Thermal Emission Imaging System) images of the Arsia Mons region near the equator of Mars. The caves (if caves they are) were given away by what look to be collapsed roofs, with the holes ranging in size from 100 to 252 metres. Several of the dark spots have been probed using thermal infrared imaging which reveals their temperature to be suspiciously consistent at any time of day or night. This suggests the dark spots are not simply pits, which would have sunlit sides and nor do they have the expected telltale rays of ejected dust that would indicate an impact origin. If they are indeed caves, then they may contain water in stable conditions, in which case their existence would be very beneficial to any future long term manned missions to Mars. The caves would make ideal ready-made dwellings for the astronauts, unless of course … they’re already occupied. More at nature.com.