On July 14, 2011, Deep Impact turned its Medium Resolution Imager toward M51, the Whirlpool Galaxy, and took 65 photos. This image is composed of 12 frames, six each through clear and red filters. Both six-filter sets were stacked to reduce the noise from cosmic ray hits. To make the color image, the clear one was placed in the green channel. A bit of the clear image was mixed with the red image to make the red channel, and the red image was subtracted from the clear image to make the blue channel. Red dots appear all over the image because there is much more noise in the red-filter images than the clear-filter images.

NASA / JPL / UMD / processed by Emily Lakdawalla