[X] My Assistant

[SigurRosFan]

Amateur photo:


--- The storm's north-south dimension is about 3,500 kilometers (2,175 miles); it is located at minus 36 degrees (planetocentric) latitude and 168 degrees west longitude. ---

Cassini (reprojected view):


- http://photojournal.jpl.nasa.gov/catalog/PIA07789 - Storm at Night (Reprojected View)

- http://photojournal.jpl.nasa.gov/catalog/PIA07788 - Storm at Night (Limb View)

- http://photojournal.jpl.nasa.gov/catalog/PIA02166 - Lightning Sounds from Saturn (Audio)

[ljk4-1]

SATURN DAILY

- Saturn Storms Dwarf Earth Hurricanes In Size And Longevity

http://www.spacedaily.com/reports/Saturn_S..._Longevity.html

Pasadena CA (SPX) Apr 20, 2006 - Viewed from space, hurricanes on Earth and the
huge atmospheric disturbances observed on Saturn look similar, but their
differences are greater, offering intriguing insights into the inner workings of
the ringed world currently being investigated by NASA's Cassini spacecraft.

[dilo]

Looking to the last raw Cassini images of Saturn atmosphere, I was intrigued by the presence of many bright spot apparently located only in the planet, especially close to terminator and more visible in the longer-exposure MT3 filtered images; absence of these spots in the dark background sky suggest they could be real features, perhaps lighting! (look at this, for example).
In order to be sure, I compared two distinct MT3 images and discovered that most bright points share exactly same positions, suggesting they are sensor related hot spots; here the result of two images subtraction:
- =
Most spots disappears but there are some residual that should be temporal variations and one of them, in particular, is relevant (in the upper/right portion of first image).
Could be lighting, but I suspect cosmic rays is the most probable cause...

[ugordan]

Could be lighting, but I suspect cosmic rays is the most probable cause...

Your third image shows that the spots are distributed even across dark sky portions and are likely less visible there in the raw images due to histogram stretching and other factors. It's pretty clear these features are just noise, if they indeed share the same pixel position between frames they are most likely to be due to accumulated CCD damage (and enhanced by a long exposure) and cosmic ray hits being the other random stuff that's left when you subtract the two images.

I don't know if lightning was so far ever visually observed at Saturn, but it seems to be located too deep below the clouds to be readily visible. The methane filter is probably not a good choice for hunting lightning, a polarizer in front of it is even worse. A special filter was placed on NAC that's very rarely used and its purpose is probably lightning detection. It's the HAL filter, which I guess stands for hydrogen alpha and thus detects emissions from ionized hydrogen.

[dilo]

Very fun, Bob . And thanks for the infos, ugordan.. I didn't know about HAL filter, anyway your explaination about bright spots sounds right (and in fact I was very skeptic about lighting explaination).

[dilo]

On May,08 Cassini Narrow-field camera taken many images of saturn atmosphere through green and CB3 filters, from about 2.8 million Km.
This is a stitch of 5 CB3 images (better showing atmospheric features):

Attached thumbnail(s)