"These features are often eyed as potential candidates for future manned missions to Mars and the moon as they provide access to naturally-occurring sub-surface caves" http://news.discovery.com/space/big-pic-mars-crater-skylight-110830.html Wes~
"These features are often eyed as potential candidates for future manned missions to Mars and the moon as they provide access to naturally-occurring sub-surface caves" http://news.discovery.com/space/big-pic-mars-crater-skylight-110830.html Wes~