Photos: Caves, water evidence found on Mars

In addition to "Annie," six other cave entrances were discovered on the Arsia Mons volcano. Together they are being called the "Seven Sisters."

The high altitude of the caves makes it unlikely that they could be used for human shelter or that microbial life would have migrated that high. But who knows what could be hiding inside them?

Photo by NASA/JPL-Caltech/ASU/USGS