This radar image shows an area near the North Pole of Mercury. The white circles or "doughnuts" may be deposits of ice on the floors of impact craters. The image, which is a few hundred kilometers across, was captured by the Arecibo radio telescope in Puerto Rico and was published in 2001.
Image courtesy of NAIC - Arecibo Observatory, a facility of the NSF (J. Harmon, P. Perrilat, and M. Slade).