Some underground Martian caves may have been spotted at the Arsia Mons region near the equator of Mars, thanks to 'skylight' holes into the caverns that have been photographed from above, researchers have said.
Glen Cushing of the US Geological Survey in Flagstaff, Arizona, got his first hint of the underground cave system from THEMIS (Mars Odyssey's Thermal Emission Imaging System) images of the Arsia Mons region, Nature magazine said.
He spotted a system of pit craters, indicative of collapsed areas, and nestled among them half a dozen dark spots ranging in diameter from 100 to 252 meters.
Two of the seven possible openings, found by Cushing, have been probed using thermal infrared imaging, which shows that their temperature is pretty constant at any time of day -- in daylight, the spots are cooler than the rest of the surface, but not as cool as shadowed areas, and at night the spots are warmer than their surroundings, Nature said.
That helps to confirm his suspicion that they are indeed holes or 'skylights' in the ceilings of underground caverns, Nature quoted Cushing as saying.
The holes don't have sunlit walls or floors, so they are not simply collapsed pits. And they don't have the rims or sprays of surrounding dust that impact craters have, he notes.
The data suggest that the holes are at least 80 metres deep, Cushing told the Lunar and Planetary Science Conference in League City, Texas, this week.
Finding such caverns on Mars, Nature says, is important for researchers keen to find a place for humans to build a base on the planet, or for those looking for signs of ancient life. Just as on Earth, caves provide shelter from the elements, particularly dust storms and temperature extremes.
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