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
Great Comet of 1744 "dust striae" seen in the tails of some comets, such as Comet West and C/2006 P1 (McNaught). Chéseaux, on March 9, was the last known observer in the northern hemisphere to see the comet, but it remained visible for observers in the southern hemisphere, some of whom reported a tail length of approximately 90 degrees on March 18. The comet was not seen after April 22, 1744. The comet also was noted in Japanese astronomical records in the "Nihon Odai Ichiran" of the Kanpō era. Researchers have found in Chinese astronomical records that some Chinese observations describe audible sounds associated