Mars Has Cave Networks, New Photos Suggest

Scott Norris
for National Geographic News
March 21, 2007
Seven circular pits on the surface of Mars appear to be openings to underground caverns, researchers have announced.

The discovery of potential caves is exciting, the scientists said, because such underground formations may be the most promising places to look for signs of life.

Researchers were able to peer into the openings from far above, using visual and infrared imaging instruments aboard the Mars orbiter Odyssey.

No bottom is visible in six of the chambers. In the seventh, a section of cave floor illuminated by direct sunlight suggests a minimum depth of about 425 feet (130 meters).

Thermal scans helped establish that the holes are probably "skylight" openings to an underground cave system. Each skylight is 330 to 820 feet (100 to 250 meters) across.

A research team presented the discovery at a meeting of the Lunar and Planetary Institute last week in Houston.

Phil Christensen, of Arizona State University in Tempe, heads the thermal imaging project on Odyssey.

He noted that temperatures at the openings remained more constant than at surrounding areas exposed to Mars' bitter nighttime temperatures.

"These pits stay relatively warm at night," Christensen said. "That suggests we're looking down into a cavern that is trapping daytime heat."

To an observer on the Martian surface, he added, "it would be a pretty spectacular view. You could stand on the edge and look in, but I'm not sure you could see the bottom."

Pits and Tubes

The openings are scattered across several hundred kilometers on the side of Mars' second highest mountain, known as Arsia Mons, near Valles Marineris (see map of Mars).

Some caves are situated high on the massive volcano, where the atmosphere is thin even by Martian standards.

Others lie on the mountain's lower flanks, where conditions may be more hospitable for life.

The surface of Mars is strewn with craters from meteor impacts and depressions formed by the collapse of underground chambers formed by flowing lava, the experts said.

Similar "collapse pits" and lava tubes with skylight openings are found in volcanic cave systems on Earth, in places such as Hawaii, the team pointed out.

The Martian caves may be similar in structure to Hawaii's lava tubes, Christensen said, albeit on a larger scale.

Smaller skylights may also be present, he added. Odyssey's thermal imager can only detect openings larger than about 330 feet (100 meters) across.

New details may come soon from additional imaging, the researchers said, as well as from the use of the high-resolution camera aboard the Mars Reconnaissance Orbiter.

Shelter From the Storm

In addition to insulation from cold temperatures, Mars' caverns may provide shelter from the barrages of dust, ultraviolet radiation, charged particles, and small meteorites that whip the planet's surface.

Some researchers have suggested that Martian caverns in low-lying areas could hold reservoirs of water, which would make the existence of microbial life much more likely.

(Read related story: "Mars Has Liquid Water, New Photos Suggest" [December 6, 2006].)

At the elevations where the caves are located, the presence of water or ice is doubtful, the Odyssey scientists said. But there remains an intriguing possibility of ongoing volcanic and hydrothermal activity in the region.

Dirk Schulze-Makuch of Washington State University headed a recent study of potential Martian hydrothermal sites including Arsia Mons.

"If there is still volcanic activity at or near the [cave] sites, the chances for life are much higher," he said.

"Hydrothermal water and associated nutrient-containing compounds could be released periodically and sustain life."

Whatever secrets the newfound caves may hold, they are likely to remain mysterious for some time. The caves' location makes them difficult if not impossible to reach with robotic rovers, the scientists said.

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