Recent images from ESA’s Mars Express spacecraft reveal long rows of crater-like depressions lining the flanks of ancient Martian volcanoes located in the planet’s vast Tharsis region. Rather than being the result of impact events, these "pit chains" were likely caused by underground lava flows, and could be a prime location for look for life. Shielded from harsh solar and cosmic radiation, the interior of such lava tubes could provide a safe haven for microbial life — especially if groundwater had found its way inside at some point.
Modified from http://www.universetoday.com/94451/coul ... thar-pits/.
Explore Mars and its volcanism with children ages 8-13 through the module Mars: Inside and Out: http://www.lpi.usra.edu/education/explore/mars/.