Deep sea mining has been off limits thus far, both because it's awfully hard, and because governments haven't yet firmed up ...

Offshore flooded caves, so-called ocean blue holes ... may exist in pockets of liquid water deep beneath the surface of Mars or in a sea under the frozen crust of Jupiter's moon Europa—to ...

Plunge into this deep blue hole and you'll discover imposing ancient ... As you descend about 410 feet below sea level, you'll discover the stalactites, but it's unlikely you'll encounter many ...