Rotating dust grains in the coma of Comet 67P/Churyumov–Gerasimenko as seen by Rosetta's OSIRIS narrow-angle camera, which was pointing 15 degrees away from the nucleus towards the Sun when it took this image on 4 March. At the time, Rosetta was 20.8 km from the comet. The image scale is 0.36m/pixel.
More details via the OSIRIS Image of the Day website.