NASA's Curiosity rover is preparing to drill for the first time, into what appears to be sedimentary rock criss-crossed by mineral-filled veins.

Back in September last year the Mars Science Laboratory carried by the rover found a rocky outcrop on the wall of Gale Crater that was full of a crusty mix of cemented pebbles. It matched signs of an alluvial-fan feature seen from orbit and was some of the very best evidence so far of significant historical water flow across the martian surface.

Now Curiosity has entered Yellowknife Bay, a terrain that exhibits all the signs of a different type of water presence. In fact this depression in the landscape seems to be entirely distinct from the earlier Gale Crater landing site about 500 meters away.

Here sedimentary rocks (formed from the crushed remains of earlier rocks) are filled with fractures and veins of what might be hydrated calcium sulfate (bassinite or gypsum) - deposited when water soaked this area. There are also nodules of deposited material, cross-bedded layering, and even a rather shiny pebble embedded in sandstone that's provoked our human pattern recognition system into thinking there's a martian 'flower' popping from the ground.

It's the perfect place for a spot of prospecting.

Over the next few days to weeks Curiosity will try out its drill, attached to the end of its 7-foot robotic arm. The drill has a bore depth of about 5 cm, enough to get well past the weathered crust of these rocks and to retrieve the grindings of an ancient martian environment.

It's not an easy task. There are concerns that a Teflon coating on the drill bit may flake off - contaminating any samples. So the first task will be to sacrifice a small amount of the upper layers of rock as an abrasive 'cleaning' material for the drill - getting rid of any Earthly contaminants before going deeper.

Once it does we'll have a new window onto Mars' deep past.