 On July 19 , 2009 , 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 this time a more compact and strong object , probably a small undiscovered asteroid , was the cause . 
