Get out your Martian spelunking gear: NASA has found what appear to be seven cave entrances on Mars. 

The Mars Odyssey spacecraft relayed images of the dark, nearly perfectly circular features ranging in diameter from 328 to 820 feet.

At first the dark spheres puzzled scientists, but Odyssey's infrared camera then checked the daytime and nighttime temperatures of the circles and suggested they were, in fact, openings to subsurface spaces. 

Odyssey’s readings showed the temperatures of the holes fluctuated only about one-third as much between day and night as the temperatures of the surrounding ground surface.

"They are cooler than the surrounding surface in the day and warmer at night," said Glen Cushing of the U.S. Geological Survey's Astrogeology Team and of Northern Arizona University, Flagstaff, Ariz.

"Their thermal behavior is not as steady as large caves on Earth that often maintain a fairly constant temperature, but it is consistent with these being deep holes in the ground."

The holes, which the researchers have dubbed the "Seven Sisters," are at very high altitudes on the planet, on a volcano named Arsia Mons near Mars' tallest mountain. They probably formed as underground stresses around the volcano caused spreading and faults that opened spaces beneath the surface.

The find has led some to wonder if these or other caves on the planet may provide shelter to life or former life on the Red Planet.

"Somewhere on Mars, caves might provide a protected niche for past or current life, or shelter for humans in the future," said Tim Titus of the U.S. Geological Survey in Flagstaff.

Read the full article at: Discovery.com

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