MESSENGER image of comet ISON (C/2012 S1) during its closest approach to Mercury. At that time, ISON was approximately 22.5 million miles (36.2 million kms) from MESSENGER and 42.1 million miles (67.8 million kms) from the Sun. The image is 7° by 4.7° in size and has been slightly magnified and smoothed to enhance the faint tail of the comet. The tail was oriented at an angle to MESSENGER at the time and is foreshortened in this image; however, some faint structure can still be seen.