How do scientists know there is ice on Mercury?

Mercury is scorched on the sunlit side, but its poles have deep craters whose floors never receive direct sunlight. Those permanently shadowed regions stay cold enough to preserve water ice for billions of years. Radar studies from Earth first detected bright reflections from the poles, and NASA’s MESSENGER mission later confirmed that the deposits are consistent with water ice and other volatile materials. This was a surprise because Mercury is so close to the Sun. The discovery showed that even the innermost planet can trap frozen water in the right conditions.