Explosion on Jupiter

[Carole]

Apparently, something hit Jupiter during the early hours of Sept. 10th (11:35 UT), igniting a ferocious fireball in the giant planet's cloudtops. Amateur astronomer Dan Peterson Racine, Wisconsin, saw it first through his Meade 12" LX200 telescope. "It was a bright white flash that lasted only 1.5 - 2 seconds,"

http://spaceweather.com/

[Rick]

[BAA-ebulletin 00696]  Fireball on Jupiter, 2012 Sep.10
(c) 2012 British Astronomical Association    http://www.britastro.org/

Fireball on Jupiter, 2012 Sep.10

A bright fireball was observed in the atmosphere of Jupiter on 2012 Sep.10 at 11:35 UT. It was similar to fireballs observed on 2010 June 3 and 2010 Aug.20, and like them, left no detectable trace on the planet's surface.

It was discovered by a visual observer, Dan Petersen in Racine, Wisconsin, who quickly notified two Jupiter contacts, giving the estimated position, time, and brightness of the flash: "This morning I witnessed an explosion on Jupiter, just inside Jupiter's eastern limb..... The flash was bright white in color, maybe about 6th magnitude in brightness and lasted for just 2 seconds."  Observers worldwide were notified at once.  Within hours another amateur, George Hall in Dallas, Texas, reported that he had the flash on a video which he was recording at the time and the flash was clearly visible. The video enabled a better estimate of the position: approx. L1 = 345, lat.+2 deg., near the edge of the orange Equatorial Band, and it appears to be brighter than mag.6.  Although the flash appears as multiple spots on the video, this was a combination of speckle pattern and diffraction pattern from an unresolved point.

Dan Petersen's report is an excellent model of how visual observers even now can make and report valuable discoveries. By informing others immediately, he enabled George Hall to find it in a video that might otherwise have gone unexamined, and he enabled his observation to be used as independent data, so there was no doubt about the reality of the fireball on Jupiter. 

Eleven hours after the impact, observers were already looking for a visible 'scar'. However, none was ever seen, neither in colour images on the first 5 rotations, nor in methane-band images taken on Sep.11 by Gary Walker and Anthony Wesley.  An illustrated report will soon be posted on the Jupiter Section web site.

So this impact was well characterised and left no 'scar', just like the two fireballs in 2010.  Scientists concluded at the time that these were impacts by miniature asteroids or comets, with diameters in the 10-metre range, which incinerated in the atmosphere above the clouds - unlike the larger impactors in 1994 and 2009.  The frequency of these events is in line with previous (very rough) estimates. They are currently being observed about once a year, but because it is so easy to overlook them, they could be occurring much more frequently (perhaps once a month?). 

John Rogers
2012 Sep.15

John H. Rogers, Ph.D.
Jupiter Section Director,
British Astronomical Association
http://www.britastro.org/jupiter/