This single frame from Rosetta's navigation camera of Comet 67P/Churyumov–Gerasimenko was taken on 25 March 2015 from a distance of 86.6 km from the comet centre, a few days before a flyby that would bring Rosetta to within about 15 km of the comet. It was during this flyby, on 28 March, that Rosetta's ROSINA instrument made a detection of the amino acid glycine in the comet's 'atmosphere', or coma.
The coma is made of gas and dust that originated from the comet nucleus. The gas is released as frozen ices are gently warmed by the Sun, dragging dust particles out into space. Studying the chemical makeup of the coma therefore provides scientists access to the composition of the materials that have been long been preserved inside the comet nucleus.
The image has a resolution of 7.4 m/pixel; this processed, cropped version measures 6.9 km across.