It appears that the sub-surface regions the entrances open into may be relatively deep - at least 70 to 100 meters - according to thermal imaging, which can only provide a minimum depth. One lucky observation, however, caught sunlight illuminating the floor of one of the caves at a depth of 130 meters. The observations were presented at the Lunar and Planetary Science Conference in Houston.

The caves are of great interest to scientists as they may be the only natural structures on Mars capable of providing protection to life. As well as offering shielding from cosmic rays, UV radiation, dust storms, micro-meteorites and solar flares, the caves also appear to have a much less harsh temperature cycle than the surface of the planet. Thermal infrared data suggest that temperatures in the caves varies relatively little between night and day (Fig. A: An optical image of the cave named "Annie", Fig. B: An afternoon thermal image showing the cave to be much cooler than the surface, Fig. C: A night image showing the cave to be much warmer than the surface).

All the caves - dubbed Dena, Chloe, Wendy, Annie, Abbey, Nikki and Jeanne - are located high up on Arsia Mons, a 20,000 meter high volcano that is second only to Olympus Mons in size. The astro-biologists in the research team believe that such a high altitude may preclude life in these seven caves, but they speculate that other caves at lower altitudes might be more conducive to biological processes. The team has already begun looking for skylight entrances at lower altitudes.

As well as harboring native Martian life, such caves may also offer future human explorers a relatively safe environment to dwell in while they explore the planet.

Source: Lunar and Planetary Science Conference