Planetary scientists have identified water ice and anomalously dark deposits within permanently shadowed regions at Mercury’s north pole.  Using data collected by NASA’s MESSENGER spacecraft, a UCLA team crafted the first accurate thermal model of the solar system’s innermost planet that successfully pinpoints extremely cold regions where ice has been found on or below the surface.  They conclude that the newly discovered black deposits are a thin dark crust of residual organic material brought to the planet over the past several million years by water-rich asteroid and comet impacts.

The New York Times has covered the findings and quotes Dave Paige: http://www.nytimes.com/2012/11/30/science/space/mercury-home-to-ice-messenger-spacecraft-findings-suggest.html?_r=0

http://planets.ucla.edu/news/water-ice-and-organics-on-mercury/