2009 Jupiter impact event

Amateur astronomer Anthony Wesley discovered the impact at approximately 13:30 UTC on 19 July 2009 (exactly 15 years after the Jupiter impacts of comet Shoemaker–Levy 9, or SL9). He was at his home observatory just outside Murrumbateman, New South Wales, Australia, using stacked images on a diameter reflecting telescope equipped with a low light machine vision video camera attached to the telescope. Wesley stated that: Wesley sent an e-mail to others including the NASA Jet Propulsion Laboratory in Pasadena, California reporting his observations. ==Findings==

Paul Kalas and collaborators confirmed the sighting. They had time on the Keck II telescope in Hawaii, and had been planning to observe Fomalhaut b, but they spent some of their time looking at the Jupiter impact. Infrared observation by Keck and the NASA Infrared Telescope Facility (IRTF) The force of the explosion on Jupiter was thousands of times more powerful than the suspected comet or asteroid that exploded over the Tunguska River Valley in Siberia in June 1908. (This would be approximately 12,500–13,000 megatons of TNT, over a million times more powerful than the bomb dropped on Hiroshima). ==Impactor==

The object that hit Jupiter was not identified before Wesley discovered the impact. A 2003 paper estimated comets with a diameter larger than 1.5 kilometers impact Jupiter about every 90 to 500 years, while a 1997 survey suggested that the astronomer Cassini may have recorded an impact in 1690. Given the size of the SL9 impactors, it is likely that this object was less than one kilometer in diameter. Finding water at the site would indicate that the impactor was a comet, as opposed to an asteroid or a very small, icy moon. At first it was believed that the object was more likely to be a comet since comets generally have more planet-crossing orbits. At the distance of Jupiter (5.2 AU) most small comets are not close enough to the Sun to be very active, and so would be hard to detect. Visibility Assuming it was an inactive comet (or asteroid) about 1 km in diameter, this object would have been no brighter than about apparent magnitude 25. Most asteroid surveys that use a wide field of view do not see fainter than about magnitude 22 (which is 16x brighter than magnitude 25). It is only since 1999 with the discovery of Callirrhoe that astronomers have been able to discover many of Jupiter's smallest moons. ==See also==