THE IMPACT OF A LARGE OBJECT ON JUPITER IN 2009 JULY

On 2009 July 19, we observed a single, large impact on Jupiter at a planetocentric latitude of 55 degrees S. This and the Shoemaker-Levy 9 (SL9) impacts on Jupiter in 1994 are the only planetary-scale impacts ever observed. The 2009 impact had an entry trajectory in the opposite direction and with a lower incidence angle than that of SL9. Comparison of the initial aerosol cloud debris properties, spanning 4800 km east-west and 2500 km north-south, with those produced by the SL9 fragments and dynamical calculations of pre-impact orbit indicates that the impactor was most probably an icy body with a size of 0.5-1 km. The collision rate of events of this magnitude may be five to ten times more frequent than previously thought. The search for unpredicted impacts, such as the current one, could be best performed in 890 nm and K (2.03-2.36 mu m) filters in strong gaseous absorption, where the high-altitude aerosols are more reflective than Jupiter's primary clouds.