NASA's release explains:
Given its proximity to the Sun, Mercury would seem to be an unlikely place to find ice. But the tilt of Mercury's rotational axis is almost zero — less than one degree — so there are pockets at the planet's poles that never see sunlight. Scientists suggested decades ago that there might be water ice and other frozen volatiles trapped at Mercury's poles.
While the discovery of water doesn't necessarily mean we'll be greeting aliens from Mercury anytime soon, NASA's scientists are interested in a possibly organic material coating the ice.
"Researchers are now working to determine if they indeed saw organics on Mercury. So far, they suspect Mercury's water ice is coated with a 4-inch (10 centimeters) blanket of 'thermally insulating material. It will take further study to figure out exactly what this material is, but Neumann said the early temperature curves could show organic materials such as amino acids." Space.com's Elizabeth Howell reports.