space.com: [...] In 1991, ground-based radar observations detected something shiny near the poles. Scientists suspect the highly reflective material to be ice. [...] Mercury does not make ice. Its axis of rotation does not precess like Earth's, so its poles have been pointing in the same direction ever since the planet was formed. Therefore, scientists figure that ice might have been deposited on Mercury by comets and other remnants of the early solar system and might have survived for a long time out of direct sunlight in the shadowy corners of deep craters.
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