The seven caves of Mars

Mars is often considered to be the most Earthlike planets in our solar system. Of course saying that requires a big leap of faith. Mars is certainly not, at least superficially, the same verdant watery world were used to calling home. However, in many ways, Mars was certainly more Earthlike in its early evolution. It exhibits remnants of its more Earthlike past. And certainly Mars geology often conjures up images of our home planets wildest deserts and most severe volcanic terrain.

At least one more kind of geological feature, familiar to us terrestrial, has now been located on Marscaverns.

NASA's Mars Odyssey spacecraft recently detected entrances to seven big cavesdubbed the Seven Sisterson the side of the giant Martian volcano Arsia Mons, or Mt. Arisa, and named after a river in Croatia.

Arsia is the K2 of Mars; it is the planets second largest mountain. The Arsia cave entrances were named Dena, Chlo묠Wendy, Annie, Abbey, Nikki, and Jeanne. Now researchers are using Mars Odyssey to search for more caverns around the Red Planet.

After examining the images from the Mars Odyssey's infrared camera, geologists agreed that what they were looking at were possibly windows into underground spaces. Measuring the shadow cast by sunlight in one of the cave pits suggests that it is 78 meters (255 feet) deep.

The IR images of these holes revealed temperature differences detected during the afternoon and morning. However, the temperatures of these holes dont change much when compared to the surrounding surface, thus the conclusion that they could be deep caves.

"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 Northern Arizona University, in Flagstaff, AZ. "Their thermal behavior . . . is consistent with these being deep holes in the ground."

The key to finding these was looking for temperature anomalies at nightwarm spots, said Phil Christensen of Arizona State University, in Tempe, principal investigator for the Thermal Emission Imaging System on Mars Odyssey. That instrument produced both visible-light and infrared images researchers used for examining the possible caves.

Whether these are just deep vertical shafts or openings into spacious caverns, they are entries to the subsurface of Mars, said Tim Titus, of the USGS. "Somewhere on Mars, caves might provide a protected niche for past or current life, or shelter for humans in the future.

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