I didn't know where to place this. Maybe and quite possibly Nick can answer.
If they're going to dig, why the North pole of Mars and not Meridiani Planum? It can't be because ice is softer.
If they have found evidence of liquid water's effects on Martian rocks at Meridiani and even Gusev, why the pole/s?
http://phoenix.lpl.arizona.edu/pdf/fact_sheet.pdf
Water ICE could have been in the poles for G-years and liquid water could have seeped the lowlands of Mars/equator and even have given rise to microbial life and the evidence of that could below those lines.
Yes, they may find water ice in the poles, but that may be it.
I had to ask.