NASA, ESA, and J.-Y. Li (Planetary Science Institute)
These Hubble telescope images show Comet Siding Spring in observations taken on March 11, 2014.
Left: In this image, the solid, icy nucleus is too small to be resolved by Hubble, but it lies at the center of a dust cloud, called a coma, that is roughly 12,000 miles across.
Right: Image processing reveals what appear to be two jets of dust coming off the nucleus in opposite directions. The jets are created when sunlight warms the comet's surface, turning the ice into gas. The gas is ejected from the comet as jets.