Comet Shoemaker–Levy 9 chains on the Jovian moons did not lead back to a larger crater. The impact of SL9 strongly implied that the chains were due to trains of disrupted cometary fragments crashing into the satellites. On July 19, 2009, exactly 15 years after the SL9 impacts, a new black spot about the size of the Pacific Ocean appeared in Jupiter's southern hemisphere. Thermal infrared measurements showed the impact site was warm and spectroscopic analysis detected the production of excess hot ammonia and silica-rich dust in the upper regions of Jupiter's atmosphere. Scientists have concluded that another impact event had occurred, but
Astronomical symbols Ω (capital omega), which was originally a typographical substitute for the astronomical symbol. The symbols for aspects first appear in Byzantine codices. Of the symbols for the five Ptolemaic aspects, only the three displayed here—for conjunction, opposition, and quadrature—are used in astronomy. Symbols for a comet (☄) and a star () have been used in published astronomical observations of comets. In tables of these observations, ☄ stood for the comet being discussed and for the star of comparison relative to which measurements of the comet's position were made. Astronomical symbols Astronomical symbols are abstract pictorial symbols used to represent astronomical