THE IMPACT OF A LARGE OBJECT ON JUPITER IN 2009 JULY

Abstract

On 2009 July 19, we observed a single, large impact on Jupiter at a\nplanetocentric latitude of 55^{\\circ}S. This and the Shoemaker-Levy 9 (SL9)\nimpacts on Jupiter in 1994 are the only planetary-scale impacts ever observed.\nThe 2009 impact had an entry trajectory opposite and with a lower incidence\nangle than that of SL9. Comparison of the initial aerosol cloud debris\nproperties, spanning 4,800 km east-west and 2,500 km north-south, with those\nproduced by the SL9 fragments, and dynamical calculations of pre-impact orbit,\nindicate that the impactor was most probably an icy body with a size of 0.5-1\nkm. The collision rate of events of this magnitude may be five to ten times\nmore frequent than previously thought. The search for unpredicted impacts, such\nas the current one, could be best performed in 890-nm and K (2.03-2.36 {\\mu}m)\nfilters in strong gaseous absorption, where the high-altitude aerosols are more\nreflective than Jupiter's primary cloud.\n