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London, Mar 17: Researchers from the US Geological Survey (USGS) have found underground caves on Mars.

The seven sister cave holes have been named Dena, Chloë, Wendy, Annie, Abbey, Nikki and Jeanne.

Glen Cushing from the USGS 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 near the equator of Mars.

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 metres.

He said two of the seven possible openings have also 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.

Though the caverns don’t have sunlit walls or floors, they have holes or 'skylights' in the ceilings of underground caverns, which in other words imply that they aren’t simply collapsed pits, he said.

“And they don't have the rims or sprays of surrounding dust that impact craters have. The data suggest that the holes are at least 80 metres deep,” Nature quoted Cushing as saying at the Lunar and Planetary Science Conference in League City, Texas, this week.

He says finding such caverns on Mars 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. On the red planet, they also protect from the rain of micro-meteorites, solar flares, ultraviolet radiation and high-energy particles from space,” he said.

Such underground caverns might also harbour stable water ice, he added.

Alfred McEwen, principal investigator on HiRISE (NASA's High-Resolution Imaging Science Experiment, on board Mars Reconnaissance Orbiter) said it’s quite plausible for caves to exist on the Red Planet.

There are volcanoes on Mars, and flowing lava would likely have formed a crust before draining away, creating a network of 'lava tube' tunnels or caves.

He is however, a little less convinced by the water-ice theory.

"Ice is not stable in contact with the martian atmosphere. It's possible to have ice in the subsurface, but not in a cave,” he said.

Bureau Report with ANI inputs