The knots of light which have been circled in yellow in this false color picture probably represent lightning in Jupiter's atmosphere. The picture was taken at 5 hours 3 minutes Universal Time on November 9, 1996 through the clear filter of the solid state imaging (CCD) system aboard NASA's Galileo spacecraft. The largest of the circled spots is over 500 kilometers across, comparable in size to the lightning events seen by NASA's Voyager 2 spacecraft in 1979, but much larger than the single lightning flashes seen by Voyager 1. Thus each of the larger circled spots represents either multiple flashes within a large lightning storm, or a single flash illuminating a much higher cloud.
The planetocentric latitude lines imposed on this image indicate that the circled events lie at about 44 degrees North latitude, just below a westward moving jet at 46 degrees North. Almost all of the Jovian lightning seen by Voyager similarly occurred near the latitude of a westward moving jet. Moreover, the circled events occurred in Jupiter's most atmospherically active high latitude region (between 36 and 46 degrees North), which is one of the zones where lightning is most likely.
In order to detect lightning the camera was scanned horizontally across the dark side of Jupiter, starting just inside the eastern edge of the planet and ending just inside its western edge. The scanning motion was employed both to cover the largest possible longitude range, and to help separate lightning strokes emanating from the same storm.
Several of the circled spots are relatively elongated in the east-west direction, perhaps due to the scanning motion of the camera (and/or to a foreshortening in the north-south direction caused by the curvature of the planet). The circled events appear well separated in space, and any apparent separation in latitude is real. Because of the scanning motion of the camera, however, these events may not have been truly separated in longitude. It is even possible that they all came from the same localized storm, and were separated principally in time.
Diffuse light covers much of this picture, and is particularly bright in the bottom righthand corner. Some of this emission may be moonlit clouds, but much of it is likely sunlight scattered into the camera by the atmosphere along Jupiter's edge.
At the time of this observation Galileo was in Jupiter's shadow, and located about 2.3 million kilometers (about 32 Jovian radii) from the planet.
The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.
This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo. Image Credit: NASA/JPL