Friday, July 23, 2004
Iapetus - giant crater still there...
Cassini's ISS system records images with a depth of 12-bits (4096 gray shades) as opposed to the personal computing standard of 8-bits (256 gray shades) in any given channel. Since the human eye can at best resolve between 16 and 20 gray shades, 8-bits is fine for the web; however, the extra depth provided by 12-bits may prove invaluble for science. However, this means that the quickie raw images put on the web will be clipped by the automatic 12 to 8-bit transistion. Only after careful reconstruction by the folks at CICLOPS do we get the full picture.
Earlier this month, I observed that Cassini appeared to have picked up a large crater in the mysterious Cassini Regio, a region covered with reddish-black material that covers the moon Iapetus' leading side. CICLOPS has rescently released a reprocessed image of Iapetus. The large crater appears to be still there - the shaded eastern scarp is visible at the edge of the regio, and there are hints of an illuminated western edge and a central peak. Now visible is the odd circular feature Voyager 1 observed at the eastern end of Cassini Regio, as well as an unnamed medium-sized crater barely detected in Voyager imagery to the south of Cassini Regio.
Andrew Gray suggested on this USENET thread that the big crater in Cassini Regio might be Roland, a 144-km wide basin seen in Voyager 2 coverage of Iapetus' north pole. The thing I am seeing is on the order of 400-km wide, and further south.
I am less certain of the gravitaion capture of the ejecta senaraio I laid out in the earlier post - it may be that I had it backward.
Cassini's ISS system records images with a depth of 12-bits (4096 gray shades) as opposed to the personal computing standard of 8-bits (256 gray shades) in any given channel. Since the human eye can at best resolve between 16 and 20 gray shades, 8-bits is fine for the web; however, the extra depth provided by 12-bits may prove invaluble for science. However, this means that the quickie raw images put on the web will be clipped by the automatic 12 to 8-bit transistion. Only after careful reconstruction by the folks at CICLOPS do we get the full picture.
Earlier this month, I observed that Cassini appeared to have picked up a large crater in the mysterious Cassini Regio, a region covered with reddish-black material that covers the moon Iapetus' leading side. CICLOPS has rescently released a reprocessed image of Iapetus. The large crater appears to be still there - the shaded eastern scarp is visible at the edge of the regio, and there are hints of an illuminated western edge and a central peak. Now visible is the odd circular feature Voyager 1 observed at the eastern end of Cassini Regio, as well as an unnamed medium-sized crater barely detected in Voyager imagery to the south of Cassini Regio.
Andrew Gray suggested on this USENET thread that the big crater in Cassini Regio might be Roland, a 144-km wide basin seen in Voyager 2 coverage of Iapetus' north pole. The thing I am seeing is on the order of 400-km wide, and further south.
I am less certain of the gravitaion capture of the ejecta senaraio I laid out in the earlier post - it may be that I had it backward.
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