Caves on Mars?

NASA’s 2001 Mars Odyssey orbiter, whose instruments have mapped frozen ice deposits and channels created by ancient flood waters on the surface of the Red Planet, has made another intriguing scientific find. NASA recently announced that the spacecraft has discovered seven holes that are likely to be the entrances to caves on the slope of Arsia Mons. The nearly circular holes, which scientists have nicknamed Dena, Chloë, Wendy, Annie, Abbey, Nikki and Jeanne, range from 100 to 250 meters in diameter, and are believed to be skylight-like openings caused by the collapse of cave ceilings. Here’s a link to a scientific paper on the discovery.

Scientists spotted the holes by comparing relative temperature differences in infrared images taken of Arsia Mons in the afternoon and in the pre-dawn morning. “They are cooler than the surrounding surface in the day and warmer at night,” explains Glen Cushing, a member of the U.S. Geological Survey’s Astrogeology Research Program.

Why are scientists so exited about seven big holes? Scientists hypothesize that if life can survive anywhere on Mars, it might be in caverns that provide a refuge from the planet’s harsh environment. As detailed in a 2005 article from Space.com, scientists envision Martian caves having conditions similar to deep caverns on Earth, such as the Lechuguilla Cave in New Mexico, where hardy bacteria survive in pools of water and feed off gases found underground.

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

Martian caves may also be useful to the human explorers who may someday visit and colonize the planet. The Web site of the NASA-funded Caves of Mars Project notes that “natural subsurface cavities and subsurface constructs present the most mission effective habitat alternative for future human missions in the high-radiation environment of Mars.” It might be easier to camp in naturally existing caves than it would be to construct above-ground settlements such as this Mars base envisioned by a British design team.

Scientists doubt, however, that the “Seven Sisters” themselves ever harbored life, because of their location on a mountainside. “Even if life has ever existed on Mars, it may not have migrated to this height,” Cushing explains.

In other Mars news, Science Daily reports that observations by another NASA probe, the Mars Reconnaissance Orbiter, are casting doubt upon what previously was seen as possible evidence of recent water flows on the surface of the planet. Last year, it was announced that images taken over a five-year period by the Mars Global Surveyor showed gullies filled with fresh deposits of what appeared to be sediment. But the Reconnaissance Orbiter’s data now suggests that those deposits may have been created by landslides of dry, loose materials, rather than by a liquid.

Other Martian gullies show evidence of liquid water flowing on Mars sometime within the last few million years, but so far, today’s Martian surface appears to be dry.