Could caves protect astronauts on Mars?

Caves were some of the earliest refuges for human beings on Earth. Could the same be true for future pioneers on Mars?

Glen Cushing, a space scientist with the U.S. Geological Survey, thinks so. He said he has found evidence for an extensive cave system among ancient volcanoes at Mars' equator.

Using images from spacecraft orbiting the Red Planet, Cushing discovered a series of "collapse depressions" in extinct lava flows from the massive Arsia Mons volcano near the planet's equator. Twelve miles high and 270 miles across, Arsia Mons is the second-largest volcano on Mars.

Cushing said these depressions are consistent with lava flows on Earth that produce caves. Flowing lava cools first on the surface, creating a hard roof, while lava continues to flow underneath. When the flow stops, what's left behind is an empty tube, kind of like the straw left when someone is finished drinking a milkshake.

Some of these Mars depressions, or grooves, are more than 60 miles long and more than 150 feet across, Cushing said.

Cushing presented his findings last week at the Geological Society of America's annual meeting in Portland, Ore.

Rich Zurek, chief Mars scientist at the Jet Propulsion Laboratory in La Canada Flintridge, Calif., said the new findings are consistent with past images of the Martian surface showing large sunken zones in the lava flows on the flanks of the big volcanoes. "We had postulated these were collapsed lava tubes," he said. "Some were tens or hundreds of meters deep."

On Earth, caves protected early man from dangerous beasts. On Mars, the danger is the environment itself, from bone-chilling cold to potentially deadly cosmic rays streaming down from space. While the Mars lander would keep out the cold, several feet of rock would do a better job of blocking cosmic rays than the thin metal skin of a spacecraft.