Travel destinations usa for This nucleus is essentially an icy ball of dirt, dust, and stones. Up close, a nucleus looks like an extraordinarily black and barren giant rock fig. Nuclei may have distinctive shapes for example, those of Comets P/Halley, P/Tempel ig , and P/Borrelly look like potatoes; those of Comets P/Tuttle and P/Hartley ig have been compared to peanuts; and, from some angles, the nucleus of Comet P/Churyumov-Gerasimenko has the appearance of a rubber duck. FIG The nucleus of Comet Tempel It measures x km. Image credit NASA/JPL/University of Maryland/Wikimedia Commons. Put simply, when a comet nucleus comes to within a certain distance from the Sun, it begins to react, its ices being converted directly from solids to gases. These gases rocket off the nucleus in jets toward the Sun and take with them dust and rock particles ig. Travel destinations usa 2016.