New Tethys Image: Banded Moon
CICLOPS has released this low resolution view of Tethys. This image highlights albedo variations seen on the surface of this satellite particularly seen at infrared wavelengths. This image was taken last month a few days after the first non-targeted encounter of Tethys and has a resolution of 8 km/pixel.
Update 04/22/2005 12:00pm - Found a great Voyager 1 image showing this dark band. According to the caption for that image:
The exact cause for the dark band is unknown, but a possible interpretation comes from recent Galileo images of Jupiter's moons Ganymede and Callisto. Both satellites exhibit light polar caps that are made from bright ice deposits on pole-facing slopes of craters. From a distance the caps appear brighter due to a haze caused by thousands of unresolved patches of ice in small craters. The dark band on Tethys may have been formed in a similar manner, consisting of hazy polar caps of unresolved bright ice patches with a dark zone in-between.
posted by Jason Perry at 10:52 AM
8 Comments:
This proposed explanation of the dark equatorial band on Tethys doesn't work very well. It only extends through about 100 degrees of longitude, and opposite it there is an even darker north-south band. Follow the equatorial band to the east and it appears to emanate from the deepest section of Ithaca Chasma. I suspect it might be a surface deposit from a short-lived plume emitted from the chasma as it formed, maybe mostly H2O but with something darker, smeared to the west by the rotation of Tethys. It can be traced around the south rim of Odysseus where it ends abruptly. I'll post images showing this when I can.
Phil Stooke
How long lived would such a deposit last? Looking at the floor of Ithaca Chasma in some of last month's images suggest to me that it is pretty old.
I don't know! And I'm not suggesting anything very specific - maybe a surface flow or periodic venting more recently, or all sorts of other possible ideas one might come up with while brainstorming! I just want to draw attenton to the odd association between this streak and the widest, deepest part of the chasma. I'm pretty certain the 'dark zone between polar deposits' explanation doesn't work.
Phil
Phil - I'd love to see the images you're talking about. Please don't keep us in suspense too long!
This URL:
http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1553.pdf
takes you to my abstract at the 2002 LPSC on this topic. It's based on reprocessing of Voyager images. Figure 1 shows the dark band I was talking about, its origin near the chasma, its abrupt end near Odysseus. Lots of other things in that abstract too! I will be trying to get all my Voyager reprocessing results up on a website eventually... but don't hold your breath.
Phil
Thanks, Phil! I won't hold my breath, but yeah, it's a really jam-packed abstract.
"All large craters (Penelope, Polyphemus etc.) on both edges of the stripe have dark albedo material on walls facing 270° longitude, and bright material on walls facing away from 270°..."
Hmm! Sounds vaguely familiar, somehow.
That issue came up when I mentioned on this blog that Penelope was quite easy to pick out in Tethys images.
That too. But I was thinking mostly about the patterns of the dark stuff on Iapetus.
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