Since cosmic radiation alters surface composition, Curiosity can drill into rock to extract pristine material from below.

CNN: Curiosity opening Martian frontier?

ExoMars, as we call it on this side of the pond, envisages a satellite to study the Martian atmosphere, followed by a large robotic rover to drill beneath the surface and cache rocks for later return to Earth.

BBC: Where now for Mars exploration?

Things get murkier still when oil companies drill deep below the surface of the ocean floor, since even robots can't go down there to see what's going on.

CNN: John D. Sutter

These maps will in turn guide partners in determining where to drill boreholes to bring the water to the surface in a cost effective manner.

UNESCO: Combating drought in the Horn of Africa

But the Icelandic outfit hopes to drill to depths of 4km or more, to get closer to the magma that rises towards the surface along local faultlines.

ECONOMIST: Geothermal energy: Blowing hot and cold | The

If all went without the tiniest hiccup, something that never happens when you are drilling five miles below the surface, and if the drilling proceeded at 150 feet per day as it has been recently, they could drill to the targeted depth in just five more days.

FORBES: Magazine Article

In the months ahead, scientists expect to probe beneath the planet's surface crust for evidence of chemistry favorable to microbial life, using the robot rover's unique high-speed drill.

WSJ: NASA's Curiosity Rover Lands on Mars