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Saturn's north pole, infrared Cassini image. Saturn is a gaseous planet composed mainly of hydrogen and helium. This image was obtained during the dark winter. The red colour is due to thermal radiation emanating from deep within the atmosphere. Darker areas are where gas clouds block out the radiation. The pole is encircled by a hexagonal feature in its atmosphere, which is thought to be caused by a planetary (atmospheric) wave. Image obtained using the infrared mapping spectrometer on board the Cassini Orbiter spacecraft. (KEYSTONE/SCIENCE PHOTO LIBRARY/NASA/JPL/GSFC/OXFORD UNIVERSITY/SCIENCE PHOTO LIBRARY)