Could Water Exist on Mercury? 

The fact that Mercury is so close to the Sun, one would automatically presume that the searing temperatures would vaporize any form of water on the surface. However, in 1991, Caltech scientists shot radio waves at Mercury and found that the reflected waves were unusually bright at the North pole. These results point to the possibility of ice on the surface.

But the question that remains is whether or not Mercury can have even the existence of water in any form. Mercury's axis of rotation is almost perpendicular to its orbital plane, meaning that the Sun is always shining on the North and South pole as the planet rotates. But scientists speculate that the interiors of large craters are never exposed to the sun and therefore have low temperatures of -161 degrees. These harsh temperatures could trap water from comets and other sources.